Download Hi-Res ImageDownload to MS-PowerPointCite This:Environ. Sci. Technol. 2019, 53, 11, 6587-6596

Strong Temperature Dependence for Light-Duty Diesel Vehicle NO_x Emissions

Stuart K. Grange*
Stuart K. Grange
Wolfson Atmospheric Chemistry Laboratories, University of York, York, YO10 5DD, United Kingdom
*E-mail: [email protected]
More by Stuart K. Grange
http://orcid.org/0000-0003-4093-3596
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Naomi J. Farren
Naomi J. Farren
Wolfson Atmospheric Chemistry Laboratories, University of York, York, YO10 5DD, United Kingdom
More by Naomi J. Farren
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Adam R. Vaughan
Adam R. Vaughan
Wolfson Atmospheric Chemistry Laboratories, University of York, York, YO10 5DD, United Kingdom
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Rebecca A. Rose
Rebecca A. Rose
Ricardo Energy & Environment, Harwell, Oxfordshire OX11 0QR, United Kingdom
More by Rebecca A. Rose
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David C. Carslaw
David C. Carslaw
Wolfson Atmospheric Chemistry Laboratories, University of York, York, YO10 5DD, United Kingdom
Ricardo Energy & Environment, Harwell, Oxfordshire OX11 0QR, United Kingdom
More by David C. Carslaw

Cite this: Environ. Sci. Technol. 2019, 53, 11, 6587–6596

Publication Date (Web):May 16, 2019

https://doi.org/10.1021/acs.est.9b01024

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Abstract

Diesel-powered road vehicles are important sources for nitrogen oxide (NO_x) emissions, and the European passenger fleet is highly dieselised, which has resulted in many European roadside environments being noncompliant with legal air quality standards for nitrogen dioxide (NO₂). On the basis of vehicle emission remote sensing data for 300000 light-duty vehicles across the United Kingdom, light-duty diesel NO_x emissions were found to be highly dependent on ambient temperature with low temperatures resulting in higher NO_x emissions, i.e., a “low temperature NO_x emission penalty” was identified. This feature was not observed for gasoline-powered vehicles. Older Euro 3 to 5 diesel vehicles emitted NO_x similarly, but vehicles compliant with the latest Euro 6 emission standard emitted less NO_x than older vehicles and demonstrated less of an ambient temperature dependence. This ambient temperature dependence is overlooked in current emission inventories but is of importance from an air quality perspective. Owing to Europe’s climate, a predicted average of 38% more NO_x emissions have burdened Europe when compared to temperatures encountered in laboratory test cycles. However, owing to the progressive elimination of vehicles demonstrating the most severe low temperature NO_x penalty, light-duty diesel NO_x emissions are likely to decrease more rapidly throughout Europe than currently thought.

Introduction

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European roadside environments remain polluted with nitrogen oxides (NO_x), and legal standards for ambient concentrations of nitrogen dioxide (NO₂), the regulated component of NO_x, are widely exceeded throughout Europe. (1,2) The lack of compliance to the legal standards has resulted in a range of potentially disruptive air quality management and intervention actions in an attempt to accelerate the reduction in concentrations to below limit values such as banning of private vehicles, low emission zones, and the introduction of progressively stringent emission standards. (3−6) The principal challenge is meeting the annual mean NO₂ of 40 μg m^–3 close to roads across European urban environments.

The recent focus for vehicle emissions research has been the quantification of the discrepancy between type approval and real-world emissions performance of diesel passenger cars. (7) Much of this focus stems from the Volkswagen diesel emission scandal, also known as “dieselgate” in late September 2015. (8−10) On-road NO_x emissions from diesel vehicles have been found to be much higher than thought prediesel emission scandal, and many Euro 6 vehicles have been found to have inadequate NO_x control when operated in real-world situations. (11−15) It has been known for many years that type approval laboratory-based emission measurements are lower than on-road measurements, and for this reason, emission factor databases such as COPERT do not use type approval emission measurements. (16)

There are a myriad reasons for discrepancies between laboratory and on-road emissions. However, there is a growing body of evidence from laboratory testing that NO_x emissions from vehicles are highly dependent on ambient temperature. (17−22) Specifically, NO_x emissions are suggested to be higher during temperatures below ≈15 °C for diesel-powered vehicles with Euro emission standards of 3 to 5 (vehicles manufactured between approximately 2000 and 2015). (17) There is also evidence for the two primary NO_x after-treatment technologies employed for Euro 6 diesel compliance: lean NO_x traps (LNT or NO_x absorbers) and selective catalytic reduction (SCR) behave differently in real world situations. (23,24) This temperature dependence needs to be thought of as independent of cold start emissions where internal combustion engines require fuel–air ratio enrichment and other strategies while the engine, lubricants, and catalytic devices reach operating temperatures which all result in greater emissions of pollutants for a short period of time. (25,26)

Type approval emission testing in Europe is performed between 20 and 30 °C. (14) While the standardization of the test cycle is a benefit from the perspective of ensuring consistent test conditions, it does not necessarily reflect prevailing ambient conditions across Europe or in many other regions of the world. The particular temperature range used for test cycles is a pragmatic choice because these temperatures are easily achieved without excessive heating or cooling requirements when vehicles are operated in laboratory settings. However, some emission factor databases such as the Handbook Emission Factors for Road Transport (HBEFA) have introduced preliminary NO_x emission correction factors, which will be revised when more data become available. (19) It is important to note that although effective NO_x control has proven to be a challenge for diesel-powered passenger vehicle manufacturers, (27,28) the technology does exist to comply with current NO_x emission limits. (14)

Despite the focus on temperature, humidity is also an important atmospheric parameter to consider for diesel and gasoline NO_x emissions. (29) High humidity within a combustion chamber offers a physical mechanism for reducing NO_x formation due to the reduction of peak flame front temperature and an increase of combustion duration. (30,31) The amount of water vapor contained in inlet air is the driver of this effect, and therefore absolute humidity (AH) is the measure used rather than relative humidity (RH). The United States MOtor Vehicle Emission Simulator (MOVES) takes humidity (and temperature) effects into account and adjusts emissions to reference conditions. (32,33) However, such adjustments do not necessarily represent real-world vehicle operation where it is important to understand such influences and their potential to affect ambient pollutant concentrations.

Low ambient temperatures are important from the perspective of the dispersion of air pollutants. During periods of low temperatures, concentrations of locally emitted, ground-level sources tend to be at their highest due to less effective dispersion resulting from stable atmospheric conditions and a lack of wind. (34) Low temperatures also result in increased emissions of many atmospheric pollutants due to increases in anthropogenic energy demands which are generally met by combustion activities. (35) When these meteorological conditions persist for several days, often an air pollution episode is experienced. The combination of meteorological factors and increased emissions due to some activities such as space heating are well documented. (36,37) However, it remains difficult to understand the relative contributions of increased source emissions and meteorological influences on the concentrations of atmospheric pollutants such as NO_x. In the case of vehicle emissions, understanding the effect of ambient temperature is of primary importance given the impact that vehicle emissions have on the exposure of urban populations.

The implications for increased NO_x emissions at lower temperatures for roadside European air quality are poorly understood but are of importance. Currently, emission inventories such as the United Kingdom National Atmospheric Emissions Inventory (NAEI) do not account for a dependence between vehicular emissions and ambient temperature, which would result in less than optimal modeling of emissions and ambient concentrations. This situation is especially relevant for cold periods where the combination of poor dispersion and increased emissions could combine, resulting in more extreme poor air quality episodes than would be expected without taking into account the temperature effect. Such an effect will be unevenly distributed throughout Europe because of the range of climatic conditions experienced. Countries or cities located in cooler areas would have been burdened with increased NO_x emissions once diesel vehicles began to significantly penetrate the European passenger vehicle fleet, beginning in the mid-1990s assuming similar diesel uptake rates. This effect would also perturb the estimations of health burdens resulting from NO_x emissions, which has been extensively considered after the diesel emission scandal. (38−40)

The effect of ambient temperature on vehicle emissions is difficult to robustly quantify using chassis dynamometers (rolling roads) or portable emission measurements systems (PEMS) because it is only practical to test a relatively small number of vehicles. (17,41) In principle, using a remote sensing technique is attractive because it offers the potential to measure far greater numbers of vehicles under a wide range of driving conditions. The remote sensing approach also offers the benefit of real-world measurements, driven by their drivers with very little chance of the vehicle detecting that it is undergoing an emissions test. (20) The remote sensing technique captures vehicles under a range of vehicle operating conditions. However, it is not possible to establish the specific operating conditions of individual vehicles such as whether they have hot or cold engines and whether vehicle aftertreatment technologies such as SCR are operating at optimum temperature. Instead, by measuring at a wide range of locations (26 in the current case) under a wide range of driving conditions, the emission characteristics of typical urban driving are quantified.

The primary objective of this work is to investigate and quantify the influence of ambient temperature on light-duty vehicle NO_x emissions using on-road remote sensing observations from field campaigns conducted between 2017 and 2018. A further objective is to consider the implications of any temperature dependence of vehicular NO_x emissions on roadside air quality in Europe.

Materials and Methods

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Measurement Locations

Remote sensing of on-road vehicle emissions was conducted in ten regions and 26 sites throughout the United Kingdom (England, Scotland, and Wales) in 2017 and 2018 (Table 1 and Figure 1). All sites were suburban in nature with the exception of the A10/M25 Junction site which was a motorway on-ramp (a slip road). The ambient temperature range experienced across these field campaigns was 0.5–24.8 °C with the greatest number of vehicle captures being conducted in the midteens (Figure S1). Such temperatures are typical for most of the United Kingdom, but there was some bias toward warmer temperatures due to more favorable field conditions. All field campaigns were conducted during Mondays and Fridays and in daylight hours (06:00–18:00), with some periods where monitoring stopped due to rain. The mean vehicle speed for valid captures was 36.1km h^–1 with a standard deviation of 9.1km h^–1.

Table 1. Information about the 26 Monitoring Sites Where on-Road Remote Sensing Took Place in 2017 and 2018^a

Site	Road ref.	Region	Lat.	Long.	Elevation (m)
Queen Margaret Drive		Glasgow	55.88	–4.29	34
Clydeside Expressway	A814	Glasgow	55.87	–4.32	9
Nelson Mandela Place		Glasgow	55.86	–4.25	16
East Mains Road	B783	South Lanarkshire	55.77	–4.17	162
Clifton Moor Gate		York	53.99	–1.09	16
Poppleton Roundabout	A59	York	53.97	–1.14	21
University of York University Road		York	53.95	–1.05	26
Barton Dock Road	B511	Manchester	53.47	–2.35	26
Stafford Street	A601	Derby	52.92	–1.48	53
Mercian Way	A601	Derby	52.92	–1.48	53
St. Quentin		Shropshire	52.67	–2.44	143
Headington	A420	Oxfordshire	51.75	–1.24	64
A10/M25 Junction	M25	London	51.68	–0.05	39
Hafod-yr-ynys Road	A472	Caerphilly	51.68	–3.12	211
Rowstock	A4185	Oxfordshire	51.60	–1.31	98
Harwell Campus out-bound		Oxfordshire	51.58	–1.31	122
Harwell Campus in-bound		Oxfordshire	51.58	–1.31	122
West End Road	A4180	London	51.57	–0.42	47
Greenford Road	A4127	London	51.52	–0.35	6
Stockley Road link	A408	London	51.51	–0.45	39
Dawley Road		London	51.50	–0.43	32
Heston Road	A3005	London	51.49	–0.37	29
Woolwich Common	A205	London	51.48	0.06	31
Putney Hill	A219	London	51.46	–0.22	37
Christchurch Road	A205	London	51.44	–0.11	59
Callington Road	A4174	Bristol	51.43	–2.56	34

^{^a}

For locations of the regions, see Figure 5.

Figure 1. Ten regions where on-road remote sensing sessions were conducted in the United Kingdom during 2017 and 2018.

Instrumentation

The equipment used to capture on-road vehicle emissions included three main components: a spectroscopic remote sensing device (RSD), speed bar lasers, and a video camera. A RSD was set up perpendicular to the flow direction of a single lane of traffic, such that the light source is directed through individual vehicle exhaust plumes. Measurements were obtained using two RS instruments: the fuel efficiency automobile test (FEAT) research instrument supplied by the University of Denver and an Opus RSD 5000. (42,43) The development and operation of the FEAT has been described elsewhere, (44−46) and an intercomparison of the two RSD instruments conducted in the United Kingdom (Leeds, England) has been previously reported. (47)

The Denver FEAT instrument consists of a nondispersive infrared (NDIR) system and a dispersive ultraviolet system. The system contains a dual-element light source (silicon carbide gas drier igniter and a xenon arc lamp) and a detector unit. The attenuation of light as it passes through the exhaust plume provides a measure of the incremental concentrations of various pollutants of interest compared to ambient background levels. Carbon monoxide (CO), carbon dioxide (CO₂), hydrocarbons (HCs), and a background reference are obtained using nondispersive infrared (IR) spectroscopy, while UV spectrometers are used to determine ammonia (NH₃), nitric oxide (NO), and NO₂. All species are quantified as a ratio to CO₂ to account for variation in the density, position, and path length of the vehicle exhaust plume. Unlike the Denver FEAT instrument, the Opus RSD 5000 does not have a dedicated spectrometer for NO₂. (47) Mean NO and NO₂ for the two instruments by the air temperatures encountered while capturing vehicles are displayed in Figure S2.

The RS instruments were calibrated in situ every few hours to account for changes in instrument performance, instrument path length, and ambient CO₂ concentrations (caused by variation in local CO₂ sources and atmospheric pressure). This was achieved using certified calibration gas cylinders containing known ratios and concentrations of gases. The cylinders used for these calibrations were different for the two instruments, and their details can be found in Table S1. Small amounts of gas from the cylinders were released into the instruments’ path to allow for a comparison of the measured ratios from the instruments to those certified by the gas cylinder manufacturer. The use of speed bar lasers alongside the RSD provided a measurement of both vehicle speed and acceleration for each passing vehicle. These variables, combined with road gradient and vehicle mass, were used to determine engine load for the vehicle at the instant it drives through the RSD path. Ratios of pollutants to CO₂ were used to derive fuel-specific emission factors in g kg^–1. The calculations used for these transformations can be found elsewhere. (44,48)

A video camera was used to photograph the vehicle registration plate of each vehicle passing the RSD. The registration plate images were digitized and sent to a data service to retrieve vehicle technical information. (49,50) The vehicle technical data included a diverse number of variables, most relevant of which were manufacturer make and model, fuel type, engine displacement, mass, type approval category, date of manufacture, and Euro status. The data are generally obtained from the Motor Vehicle Registration Information System (MVRIS). (51) Diesel Euro 6 vehicles were further manually classified by their known postcombustion NO_x control technology, either LNT or SCR systems. The classification of after-treatment technology used a number of sources, most notably Yang et al., (52) and was conducted by an expert with extensive vehicle knowledge (Sujith Kollamthodi (Ricardo Energy & Environment), personal communication, August 2017). Seventy eight percent of diesel-powered Euro 6 passenger vehicles could be classified into these two additional groups.

Data

The data sets from the measurement campaigns were processed to conform to a formal relational data model outlined in the emitr R package, and the database system used was PostgreSQL. (53−55) The data set was filtered to contain a select set of vehicles with reliable and complete vehicle technical information. The data used in the analysis consisted only of vehicle type approval categories of M1 (passenger cars) and N1 (light-duty vans <3.5 tonnes), engine types of diesel and gasoline, and vehicles with Euro status between 3 and 6. This process resulted in a set with 300000 observations with approximately 201000 unique vehicle registrations. For counts of vehicles by their type, fuel type, and Euro status, see Table S2.

Meteorological observations were sourced from meteorological monitoring sites nearby the road sections used for remote sensing and were accessed from the NOAA Integrated Surface Database (ISD). (56) The meteorological observations were joined to the vehicle capture data so every capture had an ambient temperature, relative humidity, and wind speed and direction observation. However, the data sourced from the ISD are of hourly resolution but vehicles and their emissions can be captured every few seconds. To accommodate this, the hourly observations for each session were padded to generate a time series at second resolution. The missing observations between the hour observations were then interpolated with a linear function and joined to the captured set.

Data Analysis Approach

A single RSD measurement has a sampling time of 0.5 s and therefore each capture is a snapshot of a vehicle for a short duration which may or may not represent typical driving behavior. RSD measurements benefit from not being limited to single observations and typical behavior can be determined by using large numbers of observations. Many measurements, typically hundreds, are used to form useful conclusions and illuminate average patterns. Aggregations are often used with such data to obtain mean emissions and uncertainties for groups of observations. (7) However, here, a different approach is used with statistical modeling. Rather than performing aggregations using potentially arbitrary groups (for example, a narrow range in ambient temperature), generalized additive models (GAMs) with smooth functions were used to model the data. (57) GAMs allow a convenient way to explore nonlinear relationships among variables, and the application here is simple with only one dependent variable: ambient air temperature. Models such as these can also be used in a predictive way after being developed. The smoothers used for the GAMs were thin plate regression splines, and their basis dimension term (k) was set to four. (58) These calculations were conducted with the mgcv R package. (57)

Emission Prediction

The GAMs were used to predict NO_x emissions for different air temperatures and vehicle fuel types. If the air temperature was outside the observation space used for GAM calculation (between 0.5 and 25 °C), the prediction was forced to be the extreme edge of the calibration space to avoid using the models in conditions they had not been developed with (Figure S3). This approach resulted in the optimistic handling of predicted NO_x emissions below 0.5 °C and above 25 °C because it seems likely that NO_x emissions would continue to increase at lower temperatures than those experienced in the field campaigns.

To investigate the potential spatial patterns of NO_x emission based on air temperature, European modeled surface air temperature data (variable code t2m) between 2010 and 2017 were sourced from the European Centre for Medium-Range Weather Forecasts’s (ECMWF) ERA Interim data product. (59) These data are gridded spatial raster objects and were used at the maximum spatial resolution available, 0.125 × 0.125 decimal degrees. The data were filtered to daytime periods (hours between 06:00 and 18:00) and then aggregated to annual and wintertime (December, January, February) means, and these summaries were then used to predict NO_x emissions. This spatial data manipulation was conducted with R and vector and raster extensions, (60−63) and the air temperatures used for prediction are shown in Figure S4. When calculating relative NO_x emissions, 20 °C was used as the relative temperature because this represents a conservative temperature for type approval conditions.

Results and Discussion

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Vehicular NO_x Emissions and Ambient Temperature

Light-duty diesel vehicle NO_x emissions were found to be highly dependent on ambient air temperature (Figure 2). Diesel vehicles emitted the least NO_x at the highest ambient temperature encountered of 25 °C. Average diesel NO_x emissions decreased at a rate of -0.36 g kg^–1 ° C^1– between 0 and 25 °C and had a range of 6.3 and 17g kg^–1 (a difference of 10.8 g kg^–1). These results show that there is a significant “low temperature NO_x emission penalty” for diesel-powered light-duty vehicles. NO_x emissions from gasoline-powered vehicles showed very little evidence of dependence on ambient temperature (Figure 2). NO_x emissions from diesel vehicles were higher than gasoline vehicles and were over 10g kg^–1 greater for temperatures below 14 °C (Figure 2). Diesel vehicle CO emissions showed no air temperature dependence, but gasoline-powered vehicles did display a slight low temperature penalty indicating that a small fraction of vehicles in the data set were captured below optimum operating temperature due to enriched fuel–air ratios (choking; not shown).

Figure 2. Generalized additive models (GAM) of NO_x emissions based on air temperature for light-duty diesel and gasoline-powered vehicles. The shaded zones represent the models’ standard error for the prediction.

When diesel vehicles were split by their Euro standard, the older Euro 3 to 5 vehicles emitted NO_x in a similar way and could therefore be considered a distinct group (Figure 3). Euro 6 diesel vehicles emitted less NO_x and demonstrated a weaker absolute ambient temperature dependence compared to older vehicles compliant to preceding Euro standards. For manufacturers to achieve the diesel Euro 6 NO_x compliance, additional technological development was necessary in the form of new after-treatment technology. Two principal postcombustion after-treatment technologies have been widely adopted: LNT and SCR systems. (52) The use of these technologies represent a significant step in light-duty diesel vehicle emission control, and the remote sensing observations indicate that these devices make the fleet of Euro 6 diesel distinct from older vehicles compliant to preceding Euro standards (Figure 3).

Figure 3. Generalized additive models (GAM) of NO_x emissions based on air temperature for groups of diesel-powered passenger vehicles. Passenger cars have been abbreviated to PC and further by their NO_x emission control technology: selective catalytic reduction (SCR) and lean NO_x traps (LNT). Euro 6 Light commercial vehicles (LCV) have also been displayed but without their emission control technology due to a small sample size. The shaded zones represent the models’ standard error for the prediction.

The two types of postcombustion Euro 6 diesel NO_x control technology did however demonstrate markedly different ambient temperature responses (Figure 3). On average, vehicles with LNTs were less effective at reducing NO_x emissions when compared to those equipped with SCR. LNTs also demonstrated a stronger temperature dependence than SCR. Despite LNTs showing a greater NO_x penalty, LNT and SCR vehicles converge at higher temperatures and by 25 °C, NO_x emissions were similar, and this is within the temperature range where type approval test cycles are conducted. This convergence behavior could be interpreted as potential evidence for the so-called “thermal window” where NO_x emission controls, most notably exhaust gas recirculation (EGR), are optimized for temperatures where type approval testing procedures are conducted. (17,64,65) The better on-road NO_x control achieved by SCR over LNT has also been reported elsewhere with PEMS instrumentation. (23,24)

LNTs operate under a cycle of chemical adsorption and regeneration once NO_x saturation is reached. LNT store NO_x until their reduction rates drop below a threshold, and then a regeneration is initiated by a short period of fuel-rich combustion where exhaust temperatures increase. The NO_x stored in the trap is then reduced to nitrogen and emitted out the tailpipe. Certain operating conditions are necessary before regeneration can occur efficiently, and there is evidence that while LNT performance can be very good when used in open-road and constant speed conditions, their NO_x capturing performance can be very poor in urban driving conditions. (24) This is explained by inefficient regeneration or when regeneration is not triggered when NO_x saturation has occurred, most probably due to certain other operating conditions not being met. SCR technology does not rely on the same cyclical operation principle which could explain why SCR is shown to be a better NO_x control strategy on an average based on on-road remote sensing observations (Figure 3). These insights suggest that manufacturers will most likely need to embrace SCR technology (or a combination of SCR and LNT) rather than LNT alone to ensure compliance to the increasingly stringent future European NO_x emission limits which will be tested with real driving emission (RDE) tests.

Diesel LCV compliant to Euro 6 are also shown in (Figure 3). These vehicles showed little ambient temperature dependence, but uncertainty below 5 °C and above 20 °C was higher due to fewer vehicles being sampled. These vehicles are almost exclusively equipped with SCR, and therefore their NO_x emission behavior is more similar to SCR passenger vehicles than any other group.

Diesel emission factor multipliers based on type approval temperatures (assumed to be 20 °C) are shown in Table 2. These multipliers are analogous to conformity factors used for RDE tests and are of use for modellers and those preparing emission inventories. Interestingly, despite the lower absolute NO_x emissions by Euro 6 vehicles with identified after-treatment technologies (Figure 3), these vehicles still demonstrate a significant relative low temperature NO_x emission penalty (Table 2). However, because of much lower absolute emissions, the air quality consequences of this behavior will be far less severe when compared to pre-Euro 6 vehicles.

Table 2. Relative NO_x Emission Factors from 20° C for Different Diesel Passenger Vehicles’ Euro Statuses^a

Vehicle type	0 °C	5 °C	10 °C	15 °C	20 °C	25 °C
Pre-Euro 6 PC	1.67 ± 0.37	1.44 ± 0.12	1.28 ± 0.07	1.2 ± 0.09	1 ± 0.15	0.67 ± 0.47
Euro 6 PC	1.62 ± 0.45	1.51 ± 0.15	1.43 ± 0.09	1.32 ± 0.11	1 ± 0.19	0.52 ± 0.58
Euro 6 LNT PC	1.82 ± 0.63	1.78 ± 0.23	1.68 ± 0.12	1.42 ± 0.14	1 ± 0.26	0.51 ± 0.71
Euro 6 SCR PC	2.03 ± 0.49	1.48 ± 0.16	1.14 ± 0.1	1.11 ± 0.13	1 ± 0.25	0.72 ± 0.71

^{^a}

The uncertainty around the emission factors represents the standard error of the GAM models’ predictions.

When pre-Euro 6 diesel vehicles were grouped by manufacturer, all manufacturers demonstrated evidence of a low temperature NO_x emission penalty (Figure 4). The two highest-emitting manufacturer groups, General Motors (GM) and Mazda had penalties of 9 and 8.6 g kg^–1 while BMW and Mitsubishi, the least polluting groups, had penalties of 2.4 and 2.6 g kg^–1. These findings demonstrate that some manufacturers on average had superior NO_x control than others for their pre-Euro 6 diesel vehicles. Figure 4 also shows evidence of two groups of emission behavior, perhaps demonstrating manufacturers’ preference for certain technology or strategies for NO_x emission control. The differential in emissions performance and temperature dependence seen between the different manufacturers could have implications for NO_x emissions throughout Europe. For example, countries with higher proportions of pre-Euro 6 diesel GM and Mazda vehicles in the fleet would tend to be associated with higher overall emissions of light-duty diesel NO_x emissions.

Figure 4. Average NO_x emissions for pre-Euro 6 diesel light-duty vehicles by manufacturer group between 0–10 and 20–30 °C. Only groups with at least 40 captures have been displayed, and full manufacturer group names can be found in Table S3.

Despite the focus on ambient temperature, changes in absolute humidity could be a contributory factor to help explain the results presented. Absolute humidity in cooler periods tends to be lower than during warmer periods (Figure S5), and because NO_x emissions are inversely related to humidity, some of the identified low temperature penalty could be driven by low humidity conditions. (29) However, when NO_x emissions were adjusted for ambient humidity by a common technique in an attempt to explain the dependence on ambient temperature (Equation S1), (33) the results showed a small reduction in NO_x emissions relative to ambient humidity (Figure S6) but could not explain the observed behavior seen in Figure 2 or Figure 3. Therefore, reduction in absolute humidity was a small contributing factor which did not explain the observations presented. It should also be recognized that it is questionable whether existing adjustment factors are suitable for modern light-duty vehicle fleets when characterizing their on-road and in-service emissions.

Air Quality Implications

Roadside NO_x concentrations tend to be at their highest during periods of low temperatures, and this is generally attributed to meteorological conditions being less favorable for pollutant dispersion and transportation, specifically high atmospheric stability and a lack of wind (for example, Figure S7). (66) The low temperature NO_x emission penalty demonstrated for diesel vehicles by remote sensing would have exacerbated the effect of stagnant atmospheric conditions and added an additional NO_x burden to the roadside atmosphere, which has not been accounted in emission inventories. This additional NO_x loading to the roadside atmosphere would be especially important to consider during poor air quality episodes when temperatures remain low for several days and fresh emissions sequentially add to previously emitted pollutants.

The increased NO_x emissions at low temperature from light-duty diesel vehicles would be influential for poor air quality episodes in most European locations since the mid-1990s when diesel vehicles began to significantly penetrate the passenger vehicle fleet. (67) This effect would be especially important for cooler European countries or cities such as those located in the high latitudes, located inland, or at altitude.

Figure 5 demonstrates the spatial heterogeneity of the diesel low temperature NO_x emission penalty throughout Europe using all light-duty vehicles during the 2017 and 2018 on-road remote sensing field campaigns. Urban areas located in Europe’s warmest areas such as Seville, southern Spain have suffered the smallest diesel NO_x penalty, while cities located inland and in the higher latitudes were affected to a much greater extent. Oslo (Norway) along with most of the Scandinavian Peninsula and the Baltic States (Estonia, Latvia, and Lithuania) have been burdened with up to 75% greater NO_x emissions during the winter compared to NO_x emissions at a temperature where type approval testing is performed. Even cities such as London which experience mild and maritime climates have still been burdened with 30–45% and 45–60% greater NO_x emissions from their passenger diesel vehicle fleet during the entire year and wintertime, respectively (Figure 5). Considering Europe as a whole, the low temperature emission penalty represents an average of 38% greater NO_x emissions when compared to emissions at 20 °C when using annual mean temperatures.

Figure 5. Light-duty diesel NO_x emission penalties when considering average daytime annual and wintertime air temperatures throughout Europe and fleet mix captured by the on-road remote sensing field campaigns. The diesel low NO_x emission penalty has been defined as the difference between NO_x emission for the locations’ mean air temperature and the NO_x emission at 20 °C. The labeled cities are discussed in text.

Using annual mean temperature as a metric, the coldest urban areas in Europe are located in the Baltic and Nordic regions. The urban areas located in these locations can expect to observe a decrease in their roadside NO_x concentrations at a faster rate compared to areas which experience warmer climates if the rates of passenger vehicle turnover are similar among the different locations. As the older, pre-Euro 6 diesel vehicles (with a strong absolute temperature dependence for NO_x emissions) are removed from service and replaced with new diesel vehicles compliant to the current Euro 6 standards and better after-treatment technologies or with gasoline, hybrid, or electric vehicles, the importance of the low temperature NO_x emission penalty for air quality will diminish. This decrease can be expected without any further management or intervention efforts. This effect only relies on the continuity of natural passenger fleet turnover and the current European market-shift away from diesel-powered vehicles, which indicates a positive outlook for European roadside air quality and the compliance to NO₂ ambient air quality limits.

Using Oslo and London as case studies, wintertime NO_x emissions in these cities can be compared to those predicted at a fixed 20 °C (Figure 6). At 20 °C, the reduction in NO_x emissions when comparing a pre-Euro 6 diesel and Euro 6 vehicles equipped with SCR is 7.3 g kg^–1. However, for London and Oslo, this difference increases to 10.2 and 11 g kg^–1, respectively, during the winter (Figure 6). Therefore, taking account of the ambient temperature dependence, there is a greater absolute reduction in NO_x emissions when compared to not considering temperature, which reinforces the positive outlook for European roadside NO_x concentrations. In the case of London and Oslo, this reduction is 40 and 51% greater than predicted in the case where no temperature dependence is considered, respectively. Vehicle fleets composed entirely of gasoline-powered vehicles are also shown for contrast in Figure 6 and demonstrate the difference of NO_x emissions between the two fuel types.

Figure 6. Predicted NO_x emissions for four passenger fleet composition scenarios during the wintertime for three European urban areas which experience different climates and at a fixed 20 °C.

In the wake of the Volkswagen diesel emission scandal, diesel vehicles have become less attractive than they once were in Europe. (68) New diesel car sales show a sharp decrease between 2011 and 2017 where new diesel sales went from 56% to 44% of total vehicles and is expected to continue to decrease (Figure S8). (67) The demand for and sales of passenger vehicles has not declined during the same period, so this shortfall is being met by increases in sales of gasoline-powered vehicles but also a growing portion of hybrid or electric vehicles. (67,68) In many European countries, the incentivisation of diesel vehicles, which was introduced in the mid-2000s, has been removed and extra taxes have been applied to diesel fuel and diesel vehicles. At the same time, hybrid or electric vehicles have experienced a range of governmental subsidies increasing their attraction to consumers and boosting their new car sales. (69) All these factors contribute to a positive outlook for NO_x emissions because the vehicles that demonstrate the most severe NO_x penalty are being removed from service as the passenger vehicle market changes. There is also evidence that the amount of NO₂ produced by light-duty diesel vehicles decreases with increasing vehicle mileage. (70) This observation offers yet another aspect which reinforces an optimistic outlook for European roadside NO_x and NO₂ concentration reduction.

This work exclusively frames vehicular NO_x emissions in a roadside air quality context. However, NO_x is a very important species to consider for ozone (O₃) and particulate matter (PM) formation, which are of importance from a human health perspective. The influence of the diesel low temperature NO_x emission penalty requires consideration by the O₃ and PM modeling communities because it represents precursor emission rates which are dependent on ambient temperature; this is not currently implemented and would likely alter predicted concentrations of these (and other species), especially when considering seasonal effects. For example, it may be that existing modeling underestimates wintertime NO_x emissions but overestimates summertime NO_x emissions, which would have implications for the generation of secondary pollutants. Similarly, this work only explores the European environment, but it is relevant to other markets such as the United States, even with their far lower penetration of diesel passenger vehicles because the low temperature NO_x penalty will still be active in other markets.

This work discusses on-road emission measurements within an ambient temperature range of 0.5–25 °C. Follow-up work should aim to extend this temperature range. To extend these temperatures, cooler and warmer locations outside the United Kingdom need to be targeted with the same on-road remote sensing technique so the lower and higher temperatures relevant to the European and other climates can be added to a future analysis and characterized.

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.9b01024.

Details of the gas cylinders used for the field calibrations, counts of captured vehicles based on vehicle type, full names of manufacturer groups, number of vehicle captures, mean NO and NO₂ emissions as captured for both RSD instruments, an example of GAM extrapolation behavior, mean annual and wintertime surface air temperatures for Europe, mean monthly absolute humidity for selected European cities, generalized additive models (GAM) of NO_x emissions with and without humidity corrections applied, ambient NO_x concentrations dependence on air temperature, market share of diesel-powered passenger vehicles, and equation used to correct NO_x emissions for ambient humidity (PDF)

es9b01024_si_001.pdf (1.0 MB)

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Corresponding Author
- Stuart K. Grange - Wolfson Atmospheric Chemistry Laboratories, University of York, York, YO10 5DD, United Kingdom; http://orcid.org/0000-0003-4093-3596; Email: [email protected]
Authors
- Naomi J. Farren - Wolfson Atmospheric Chemistry Laboratories, University of York, York, YO10 5DD, United Kingdom
- Adam R. Vaughan - Wolfson Atmospheric Chemistry Laboratories, University of York, York, YO10 5DD, United Kingdom
- Rebecca A. Rose - Ricardo Energy & Environment, Harwell, Oxfordshire OX11 0QR, United Kingdom
- David C. Carslaw - Wolfson Atmospheric Chemistry Laboratories, University of York, York, YO10 5DD, United Kingdom; Ricardo Energy & Environment, Harwell, Oxfordshire OX11 0QR, United Kingdom
Notes
The authors declare no competing financial interest.

Acknowledgments

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The authors thank Anthony Wild for the provision of the Wild Fund Scholarship awarded to S.K.G.. Ricardo Energy & Environment’s on-road remote sensing field team, especially Ben Fowler, Tom Green, and Les Phelp, are thanked for their work in collecting data with the Opus instrument, as are Will Drysdale and Stuart Young from the University of York for their help with operating the FEAT instrument. Sujith Kollamthodi from Ricardo Energy & Environment is acknowledged for identifying the after-treatment technologies on diesel passenger cars. We thank the International Council on Clean Transportation (ICCT) for their support in funding some of the measurements made in London. Finally, this work was supported by the Natural Environment Research Council (NERC).

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Regulated and unregulated emissions from two Euro 6b diesel passenger cars tested using three different blends of hydrotreated vegetable oil (HVO), fossil diesel and com. diesel (B7) were investigated at 23 °C and -7 °C using the World harmonized Light-duty vehicle Test Procedure at the Vehicle Emission Lab. of the European Commission Joint Research Center Ispra, Italy. The HVO blends used were: Neat HVO (100 vol% HVO), 30 vol% HVO and 7 vol% HVO. One of the vehicles was also tested using the three HVO blends on-road following a RDE compliant route. Overall, the use of different HVO blends and diesel did not lead to fuel related trends on the emissions of the tested vehicles in the lab. nor on-road. However, HVO-100 resulted in ∼4% lower CO2 emissions than the other fuel tested in all the studied conditions. Low ambient temp. caused an increase of the emissions of studied compds. (with the exception of NH3) with all tested blends. The exptl. results showed that in many cases the obsd. outcomes were probably attributable to a combination of combustion effects, after-treatment effects, and their control strategy.
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Cha, J.; Lee, J.; Chon, M. S. Evaluation of real driving emissions for Euro 6 light-duty diesel vehicles equipped with LNT and SCR on domestic sales in Korea. Atmos. Environ. 2019, 196, 133– 142, DOI: 10.1016/j.atmosenv.2018.09.029
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Evaluation of real driving emissions for Euro 6 light-duty diesel vehicles equipped with LNT and SCR on domestic sales in Korea
Cha, Junepyo; Lee, Jongtae; Chon, Mun Soo
Atmospheric Environment (2019), 196 (), 133-142CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
In general, recent certification procedure for regulatory emission limits is used to the std. test cycles in the lab. under standardized operating conditions. But, it is proving that the real driving emissions (RDE) of vehicles highly exceed the std. emission limits. In order to tackle this problem, RDE regulation has been proposed with the Potable Emissions Measurement Systems (PEMS). In present study, the PEMS (Portable Emissions Measurement System) equipment, which consists of an exhaust gas flow meter, an exhaust gas sampling device, an exhaust gas analyzer, an OBD data acquisition device, GPS and ambient air sensors, and power supplying device, is installed on 17 test vehicles (Euro 6) sold in Korea currently. And two test driving routes (Route A and B) under 3rd RDE package were developed to include Seoul into urban driving due to reflecting representative traffic and road conditions in Korea. In results, the av. NOx emissions of most test vehicles approx. exceeded 6.6 times the emission limit on test routes. Addnl., the on-road NOx emissions of test vehicles by applying SCR during the same trip were not relatively different based on the ambient temps. With respect to most test vehicles, the CO2 emissions in the urban section are generally higher than those in the total trip.
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Ko, J.; Myung, C.-L.; Park, S. Impacts of ambient temperature, DPF regeneration, and traffic congestion on NO_x emissions from a Euro 6-compliant diesel vehicle equipped with an LNT under real-world driving conditions. Atmos. Environ. 2019, 200, 1– 14, DOI: 10.1016/j.atmosenv.2018.11.029
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Impacts of ambient temperature, DPF regeneration, and traffic congestion on NOx emissions from a Euro 6-compliant diesel vehicle equipped with an LNT under real-world driving conditions
Ko, Jinyoung; Myung, Cha-Lee; Park, Simsoo
Atmospheric Environment (2019), 200 (), 1-14CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
A real driving emissions test procedure was introduced as a supplement to the chassis dynamometer test to diminish the discrepancy between on-road emissions and type approval certification emissions. In this study, on-road NOx emissions from a 2.2 L diesel vehicle equipped with a lean NOx trap were measured not by a portable emissions measurement system but by NOx sensors and an exhaust flow meter. This method provides a strategy for analyzing on-road NOx emissions with a measurement system that is relatively cheap, light and simple. The effects of ambient temp., diesel particulate filter regeneration, traffic congestion, NOx conversion efficiency and uphill/downhill sections on NOx emissions were evaluated by comparing the NOx emissions characteristics using engine-out and lean NOx trap-out NOx sensors. NOx emissions in congested traffic conditions were 29% higher than those in smooth traffic conditions. NOx emissions at 33 °C were 55% higher than those at 27 °C. Addnl., NOx emissions under specific conditions with diesel particulate filter regeneration were 30% higher than those under normal conditions. The av. on-road NOx emission factor for all test cases was 7.35, but this value decreased to 5.7 when an ambient temp. corrective factor (1.6) was applied for extended test conditions.
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Weilenmann, M.; Favez, J.-Y.; Alvarez, R. Cold-start emissions of modern passenger cars at different low ambient temperatures and their evolution over vehicle legislation categories. Atmos. Environ. 2009, 43, 2419– 2429, DOI: 10.1016/j.atmosenv.2009.02.005
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Cold-start emissions of modern passenger cars at different low ambient temperatures and their evolution over vehicle legislation categories
Weilenmann, Martin; Favez, Jean-Yves; Alvarez, Robert
Atmospheric Environment (2009), 43 (15), 2419-2429CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
The emissions of modern gasoline and diesel passenger cars are reduced by catalysts except in cold-starting. Since catalysts require a certain temp. (typically above 300 °C) to work to full efficiency, emissions are significantly higher during the warm-up phase of the car. The duration of this period and the emissions produced depend on the ambient temp. as well as on the initial temp. of the car's propulsion systems. The addnl. emissions during a warm-up phase, known as "cold-start extra emissions" (CSEEs) for emission inventory modeling, are mostly assessed by emission measurements at an ambient temp. of 23 °C. However, in many European countries av. ambient temps. are below 23 °C. This necessitates emission measurements at lower temps. in order to model and assess cold-start emissions for real-world temp. conditions. This paper investigates the influence of regulated pollutants and CO2 emissions of recent gasoline and diesel car models (Euro-4 legislation) at different ambient temps., 23, -7 and -20 °C. We present a survey and model of the evolution of cold-start emissions as a function of different car generations (pre-Euro-1 to Euro-4 legislations). In addn. the contribution of CSEEs to total fleet running emissions is shown to highlight their increasing importance. For gasoline cars, it turns out that in av. real-world driving the majority of the CO (carbon monoxide) and HC (hydrocarbon) total emissions are due to cold-start extra emissions. Moreover, the cold-start emissions increase considerably at lower ambient temps. In contrast, cold-start emissions of diesel cars are significantly lower than those of gasoline cars. Furthermore, the transition from Euro-3 to Euro-4 gasoline vehicles shows a trend for a smaller decline for cold-start extra emissions than for legislative limits. Particle and NOx emission of cold-starts are less significant.
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Roberts, A.; Brooks, R.; Shipway, P. Internal combustion engine cold-start efficiency: A review of the problem, causes and potential solutions. Energy Convers. Manage. 2014, 82, 327– 350, DOI: 10.1016/j.enconman.2014.03.002
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Carslaw, D. C.; Murrells, T. P.; Andersson, J.; Keenan, M. Have vehicle emissions of primary NO₂ peaked?. Faraday Discuss. 2016, 189, 439– 454, DOI: 10.1039/C5FD00162E
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Have vehicle emissions of primary NO2 peaked?
Carslaw, David C.; Murrells, Tim P.; Andersson, Jon; Keenan, Matthew
Faraday Discussions (2016), 189 (Chemistry in the Urban Atmosphere), 439-454CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)
Reducing ambient concns. of nitrogen dioxide (NO2) remains a key challenge across many European urban areas, particularly close to roads. This challenge mostly relates to the lack of redn. in emissions of oxides of nitrogen (NOx) from diesel road vehicles relative to the redns. expected through increasingly stringent vehicle emissions legislation. However, a key component of near-road concns. of NO2 derives from directly emitted (primary) NO2 from diesel vehicles. It is well-established that the proportion of NO2 (i.e. the NO2/NOx ratio) in vehicle exhaust has increased over the past decade as a result of vehicle after-treatment technologies that oxidise carbon monoxide and hydrocarbons and generate NO2 to aid the emissions control of diesel particulate. In this work we bring together an anal. of ambient NOx and NO2 measurements with comprehensive vehicle emission remote sensing data obtained in London to better understand recent trends in the NO2/NOx ratio from road vehicles. We show that there is evidence that NO2 concns. have decreased since around 2010 despite less evidence of a redn. in total NOx. The decrease is shown to be driven by relatively large redns. in the amt. of NO2 directly emitted by vehicles; from around 25 vol% in 2010 to 15 vol% in 2014 in inner London, for example. The anal. of NOx and NO2 vehicle emission remote sensing data shows that these redns. have been mostly driven by reduced NO2/NOx emission ratios from heavy duty vehicles and buses rather than light duty vehicles. However, there is also evidence from the anal. of Euro 4 and 5 diesel passenger cars that as vehicles age the NO2/NOx ratio decreases. For example the NO2/NOx ratio decreased from 29.5 ± 2.0% in Euro 5 diesel cars up to one year old to 22.7 ± 2.5% for four-year old vehicles. At some roadside locations the redns. in primary NO2 have had a large effect on reducing both the annual mean and no. of hourly exceedances of the European Limit Values of NO2.
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Myung, C.-L.; Jang, W.; Kwon, S.; Ko, J.; Jin, D.; Park, S. Evaluation of the real-time de-NO_x performance characteristics of a LNT-equipped Euro-6 diesel passenger car with various vehicle emissions certification cycles. Energy 2017, 132, 356– 369, DOI: 10.1016/j.energy.2017.05.089
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Evaluation of the real-time de-NOx performance characteristics of a LNT-equipped Euro-6 diesel passenger car with various vehicle emissions certification cycles
Myung, Cha-Lee; Jang, Wonwook; Kwon, Sangil; Ko, Jinyoung; Jin, Dongyoung; Park, Simsoo
Energy (Oxford, United Kingdom) (2017), 132 (), 356-369CODEN: ENEYDS; ISSN:0360-5442. (Elsevier Ltd.)
Advanced nitrogen oxides (NOx) after-treatment systems for diesel cars are effectively reducing tailpipe NOx emissions in lab. test cycles; however, some de-NOx systems showed limitation for passing environmental stds. during real-world driving conditions. In this study, the NOx concn. of a lean NOx trap (LNT)-equipped diesel engine were investigated over various vehicle certification cycles. The LNT performance was compared to the new European driving cycle (NEDC), world-harmonized light-duty vehicle test cycle (WLTC), federal test procedure (FTP)-75, highway fuel economy test (HWFET), and US06. The real-time NOx concn. behaviors were tracked using NOx sensors at the engine-out and downstream of the LNT to det. the NOx storage and regeneration phase. The NOx conversion efficiencies were 36.3-71.7% of which reflecting the mode severity and cycle duration of the diesel engine. The tailpipe NOx emissions were 0.059 g/km during the NEDC which was within the Euro-6 emissions regulations. The NOx emissions in the WLTC, FTP-75, and US06 modes were approx. 1.9, 1.5, and 6.6 times higher than the NEDC due to the higher frequency of LNT purge and higher engine-out NOx formation. During the diesel particulate filter (DPF) regenerating stage in WLTC mode, tailpipe NOx emissions substantially increased by more than 8.8-fold. The exhaust gas recirculation (EGR) supply and lambda control scheme were closely related with strong NOx increment at de-NOx and de-PM processes.
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Lindhjem, C.; Chan, L.-M.; Pollack, A.; Kite, C. Applying Humidity and Temperature Corrections to On and Off-Road Mobile Source Emissions. 2004; https://www3.epa.gov/ttnchie1/conference/ei13/mobile/lindhjem.pdf, (accessed May 14, 2019).
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Rakopoulos, C. D. Ambient temperature and humidity effects on the performance and nitric oxide emission of spark ignition engined vehicles in Athens/Greece. Solar & Wind Technology 1988, 5, 315– 320, DOI: 10.1016/0741-983X(88)90031-8
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Chang, Y.; Mendrea, B.; Sterniak, J.; Bohac, S. V. Effect of Ambient Temperature and Humidity on Combustion and Emissions of a Spark-Assisted Compression Ignition Engine. J. Eng. Gas Turbines Power 2017, 139, 051501– 051501–7, DOI: 10.1115/1.4034966
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Effect of ambient temperature and humidity on combustion and emissions of a spark-assisted compression ignition engine
Chang, Yan; Mendrea, Brandon; Sterniak, Jeff; Bohac, Stanislav V.
Journal of Engineering for Gas Turbines and Power (2017), 139 (5), 051501/1-051501/7CODEN: JETPEZ; ISSN:1528-8919. (American Society of Mechanical Engineers)
Spark-assisted compression ignition (SACI) offers more practical combustion phasing control and a lower pressure rise rate than homogeneous charge compression ignition (HCCI) combustion and improved thermal efciency and lower NOx emissions than spark ignition (SI) combustion. Any practical passenger car engine, including one that uses SACI in part of its operating range, must be robust to changes in ambient conditions. This study investigates the effects of ambient temp. and humidity on stoichiometric SACI combustion and emissions. It is shown that at the medium speed and load SACI test point selected for this study, increasing ambient air temp. from 20°C to 41 #x00B0;C advances combustion phasing, increases max. pressure rise rate, causes a larger fraction of the charge to be consumed by auto-ignition (and a smaller fraction by ame propagation), and increases NOx. Increasing ambient humidity from 32% to 60% retards combustion phasing, reduces max. pressure rise rate, increases coefcient of variation (COV) of indicated mean effective pressure (IMEP), reduces NOx, and increases brake-specic fuel consumption (BSFC). These results show that successful implementation of SACI combustion in real-world driving requires a control strategy that compensates for changes in ambient temp. and humidity.
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U.S. Environmental Protection Agency, Emission Adjustments for Temperature, Humidity, Air Conditioning, and Inspection and Maintenance for On-road Vehicles in MOVES2014. 2014; Assessment and Standards Division Office of Transportation and Air Quality U.S. Environmental Protection Agency. EPA-420-R-14–012. December 2014 (accessed May 14, 2019).
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There is no corresponding record for this reference.
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U.S. Environmental Protection Agency, Derivation of Humidty and NO_x Humidty Correction Factors. 2016; https://www.epa.gov/sites/production/files/2015-09/documents/noxcorr.pdf, US-EPA-OAR-OMS-TSD (accessed May 14, 2019).
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Mayer, H. Air pollution in cities. Atmos. Environ. 1999, 33, 4029– 4037, DOI: 10.1016/S1352-2310(99)00144-2
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Air pollution in cities
Mayer, Helmut
Atmospheric Environment (1999), 33 (24-25), 4029-4037CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science Ltd.)
The review with 24 refs. Air quality in cities is the result of a complex interaction between natural and anthropogenic environmental conditions. Air pollution in cities is a serious environmental problem - esp. in the developing countries. The air pollution path of the urban atm. consists of emission and transmission of air pollutants resulting in the ambient air pollution. Each part of the path is influenced by different factors. Emissions from motor traffic are a very important source group throughout the world. During transmission, air pollutants are dispersed, dild. and subjected to photochem. reactions. Ambient air pollution shows temporal and spatial variability. As an example of the temporal variability of urban air pollutants caused by motor traffic, typical av. annual, weekly and diurnal cycles of Nitric oxide, NO2, O3 and Ox are presented for an official urban air-quality station in Stuttgart, southern Germany. They are supplemented by weekly and diurnal cycles of selected percentile values of NO, NO2, and O3. Time series of these air pollutants give information on their trends. Results are discussed with regard to air pollution conditions in other cities. Possibilities for the assessment of air pollution in cities are shown. In addn., a qual. overview of the air quality of the world's megacities is given.
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Fenger, J. Air pollution in the last 50 years - From local to global. Atmos. Environ. 2009, 43, 13– 22, DOI: 10.1016/j.atmosenv.2008.09.061
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Air pollution in the last 50 years - From local to global
Fenger, Jes
Atmospheric Environment (2008), 43 (1), 13-22CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
A review. Air pollution in the industrialized world has in the last 50 years undergone drastic changes. Until after World War II the most important urban compd. was SO2 combined with soot from the use of fossil fuels in heat and power prodn. When that problem was partly solved by cleaner fuels, higher stacks, and flue gas cleaning in urban areas, the growing traffic gave rise to NOx and volatile org. compds. and in some areas photochem. air pollution, which may be abated by catalytic converters. Lately the interest has centered on small particles and more exotic org. compds. that can be detected with new sophisticated anal. techniques. Simultaneously with the development in compds., the time and geog. scale of interest have increased. First to transboundary air pollution, which in decades and on continents can degrade ecosystems, later to the depletion of the ozone layer and esp. to the increasing greenhouse effect with climate change that will change the conditions for nature and mankind on the entire globe. The possibilities to study these large scale phenomena were greatly enhanced by the development of electronic computers that can handle large data sets and calc. various scenarios. All these processes take place in the thin layer of gases around the Earth, the atm. Although the abatement is often restricted to a single aspect, they are often connected and should when possible be treated as whole.
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Scott, A. J.; Scarrott, C. Impacts of residential heating intervention measures on air quality and progress towards targets in Christchurch and Timaru, New Zealand. Atmos. Environ. 2011, 45, 2972– 2980, DOI: 10.1016/j.atmosenv.2010.09.008
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Impacts of residential heating intervention measures on air quality and progress towards targets in Christchurch and Timaru, New Zealand
Scott, Angelique J.; Scarrott, Carl
Atmospheric Environment (2011), 45 (17), 2972-2980CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
Elevated wintertime particulate concns. in the New Zealand cities of Christchurch and Timaru are mostly attributed to the burning of wood and coal for residential heating. A carrot-and-stick approach was adopted for managing air quality in Christchurch, where strict intervention measures were introduced together with a residential heater replacement program to encourage householders to change to cleaner forms of heating. A similar approach was only recently implemented for Timaru. This paper presents the results of a partial accountability anal., where the impact of these measures on the target source, PM10 emissions, and PM10 concns. are quantified. A statistical model was developed to est. trends in the concns., which were tested for significance after accounting for meteorol. effects, and to est. the probability of meeting air quality targets. Results for Christchurch and Timaru are compared to illustrate the impacts of differing levels of intervention on air quality. In Christchurch, approx. 34,000 (76%) open fires and old solid fuel burners were replaced with cleaner heating technol. from 2002 to 2009, and total open fires and solid fuel burner nos. decreased by 45%. Over the same time period, estd. PM10 emissions reduced by 71% and PM10 concns. by 52% (maxima), 36% (winter mean), 26% (winter median) and 41% (meteorol.-adjusted winter means). In Timaru, just 3000 (50%) open fires and old solid fuel burners were replaced from 2001 to 2008, with total open fire and solid fuel burner nos. reduced by 24%. PM10 emissions declined by 32%, with low redns. in the PM10 concns. (maxima decreased by 7%, winter means by 11% and winter medians by 3%). These findings, supported by the results of the meteorol. cor. trend anal. for Christchurch, strongly indicate that the combination of stringent intervention measures and financial incentives has led to substantial air quality improvements in the city. The lesser impact of more lenient rules and the late introduction of an incentives program are obvious on air quality in Timaru. Trends established for the two cities were extrapolated under various scenarios to det. the likelihood of meeting air quality targets. In Christchurch the probability of compliance is low and is essentially impossible for Timaru if recent trends continue.
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Grange, S. K.; Salmond, J. A.; Trompetter, W. J.; Davy, P. K.; Ancelet, T. Effect of atmospheric stability on the impact of domestic wood combustion to air quality of a small urban township in winter. Atmos. Environ. 2013, 70, 28– 38, DOI: 10.1016/j.atmosenv.2012.12.047
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Effect of atmospheric stability on the impact of domestic wood combustion to air quality of a small urban township in winter
Grange, S. K.; Salmond, J. A.; Trompetter, W. J.; Davy, P. K.; Ancelet, T.
Atmospheric Environment (2013), 70 (), 28-38CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
In the winter of 2011, a field campaign was undertaken in the small township of Nelson, New Zealand to measure the vertical and horizontal distribution of concns. of airborne particulate matter. The aim was to improve our understanding of the causal factors which result in periods of very high concns. of particulate pollution in small townships during winter where emissions are dominated by the combustion of wood for domestic heating. The results showed that mean hourly surface concns. of particulates throughout the airshed were characterized by a distinctive diurnal cycle, with 2 peaks in concn. (one in the late evening and then, unusually, a 2nd mid-morning). Although the timing and magnitude of hourly peak concns. was variable throughout the valley, there was no evidence to suggest that regional or topog. flows played a significant role in the build-up of pollutants at any given location. Anal. of vertical profiles of black C showed that high concns. of particulates were confined to the lowest 50 m of the boundary layer. Concns. decreased with increasing height within this polluted surface layer. The atmosphere was very stable during the evening period. After midnight, a period of increased mixing was consistently identified throughout the lowest 100 m of the boundary layer and assocd. with the sudden cleansing of the surface and lower layers of the boundary layer. Throughout the observational period there was no evidence for the storage of pollutants aloft. Thus the vertical mixing of pollutants to the surface could not account for increased pollutant concns. during the morning period. However, at this time the boundary layer remained stable and concns. of black carbon were mixed through a very shallow layer. This suggests that despite lower domestic heating emissions in the morning, the reduced mixing vol. is a likely cause of the obsd. marked peak in morning surface concns.
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Anenberg, S. C.; Miller, J.; Minjares, R.; Du, L.; Henze, D. K.; Lacey, F.; Malley, C. S.; Emberson, L.; Franco, V.; Klimont, Z.; Heyes, C. Impacts and mitigation of excess diesel-related NO_x emissions in 11 major vehicle markets. Nature 2017, 545, 467– 471, DOI: 10.1038/nature22086
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Impacts and mitigation of excess diesel-related NOx emissions in 11 major vehicle markets
Anenberg, Susan C.; Miller, Joshua; Minjares, Ray; Du, Li; Henze, Daven K.; Lacey, Forrest; Malley, Christopher S.; Emberson, Lisa; Franco, Vicente; Klimont, Zbigniew; Heyes, Chris
Nature (London, United Kingdom) (2017), 545 (7655), 467-471CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
Vehicle emissions contribute to fine particulate matter (PM2.5) and tropospheric O3 air pollution, affecting human health, crop yields, and climate worldwide. On-road diesel vehicles produce ∼20% of global anthropogenic NOx emissions, which are key PM2.5 and O3 precursors. Regulated NOx emission limits in leading markets have progressively tightened, but current diesel vehicles emit far more NOx under actual operating conditions vs. lab. certification testing. This work showed that across 11 markets representing ∼80% of global diesel vehicle sales, nearly one-third of on-road heavy-duty diesel vehicle emissions and more than half the on-road light-duty diesel vehicle emissions are in excess of certification limits. These excess emissions (totaling 4.6 million tons) are assocd. with ∼38,000 PM2.5- and O3-related premature deaths globally in 2015, including ∼10% of all O3-related premature deaths in the 28 European Union member states. Heavy-duty vehicles are the dominant contributor to excess diesel NOx emissions and assocd. health impacts in nearly all regions. Adopting and enforcing next-generation stds. (more stringent than Euro 6/VI) could nearly eliminate actual diesel-related NOx emissions in these markets, avoiding ∼174,000 global PM2.5- and O3-related premature deaths in 2040. Most of these benefits can be achieved by implementing Euro VI stds. where they have not yet been adopted for heavy-duty vehicles.
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Chossière, G. P.; Malina, R.; Ashok, A.; Dedoussi, I. C.; Eastham, S. D.; Speth, R. L.; Barrett, S. R. H. Public health impacts of excess NO_x emissions from Volkswagen diesel passenger vehicles in Germany. Environ. Res. Lett. 2017, 12, 034014, DOI: 10.1088/1748-9326/aa5987
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Public health impacts of excess NOx emissions from Volkswagen diesel passenger vehicles in Germany
Chossiere, Guillaume P.; Malina, Robert; Ashok, Akshay; Dedoussi, Irene C.; Eastham, Sebastian D.; Speth, Raymond L.; Barrett, Steven R. H.
Environmental Research Letters (2017), 12 (3), 034014/1-034014/14CODEN: ERLNAL; ISSN:1748-9326. (IOP Publishing Ltd.)
In Sept. 2015, the Volkswagen Group (VW) admitted the use of 'defeat devices' designed to lower emissions measured during VW vehicle testing for regulatory purposes. Globally, 11 million cars sold between 2008 and 2015 are affected, including about 2.6 million in Germany. On-road emissions tests have yielded mean on-road NOx emissions for these cars of 0.85 g km-1, over four times the applicable European limit of 0.18 g km-1. This study ests. the human health impacts and costs assocd. with excess emissions from VW cars driven in Germany. A distribution of on-road emissions factors is derived from existing measurements and combined with sales data and a vehicle fleet model to est. total excess NOx emissions. These emissions are distributed on a 25 by 28 km grid covering Europe, using the German Environmental Protection Agency's (UBA) est. of the spatial distribution of NOx emissions from passenger cars in Germany. We use the GEOS-Chem chem.-transport model to predict the corresponding increase in population exposure to fine particulate matter and ozone in the European Union, Switzerland, and Norway, and a set of concn.-response functions to est. mortality outcomes in terms of early deaths and of life-years lost. Integrated over the sales period (2008-2015), we est. median mortality impacts from VW excess emissions in Germany to be 1 200 premature deaths in Europe, corresponding to 13 000 life-years lost and 1.9 billion EUR in costs assocd. with life-years lost. Approx. 60% of mortality costs occur outside Germany. For the current fleet, we est. that if on-road emissions for all affected VW vehicles in Germany are reduced to the applicable European emission std. by the end of 2017, this would avert 29 000 life-years lost and 4.1 billion 2015 EUR in health costs (median ests.) relative to a counterfactual case with no recall.
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Abstract
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Figure 1
Figure 1. Ten regions where on-road remote sensing sessions were conducted in the United Kingdom during 2017 and 2018.
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Figure 2
Figure 2. Generalized additive models (GAM) of NO_x emissions based on air temperature for light-duty diesel and gasoline-powered vehicles. The shaded zones represent the models’ standard error for the prediction.
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Figure 3
Figure 3. Generalized additive models (GAM) of NO_x emissions based on air temperature for groups of diesel-powered passenger vehicles. Passenger cars have been abbreviated to PC and further by their NO_x emission control technology: selective catalytic reduction (SCR) and lean NO_x traps (LNT). Euro 6 Light commercial vehicles (LCV) have also been displayed but without their emission control technology due to a small sample size. The shaded zones represent the models’ standard error for the prediction.
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Figure 4
Figure 4. Average NO_x emissions for pre-Euro 6 diesel light-duty vehicles by manufacturer group between 0–10 and 20–30 °C. Only groups with at least 40 captures have been displayed, and full manufacturer group names can be found in Table S3.
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Figure 5
Figure 5. Light-duty diesel NO_x emission penalties when considering average daytime annual and wintertime air temperatures throughout Europe and fleet mix captured by the on-road remote sensing field campaigns. The diesel low NO_x emission penalty has been defined as the difference between NO_x emission for the locations’ mean air temperature and the NO_x emission at 20 °C. The labeled cities are discussed in text.
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Figure 6
Figure 6. Predicted NO_x emissions for four passenger fleet composition scenarios during the wintertime for three European urban areas which experience different climates and at a fixed 20 °C.
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  Implications of diesel emissions control failures to emission factors and road transport NOx evolution
  Ntziachristos, Leonidas; Papadimitriou, Giannis; Ligterink, Norbert; Hausberger, Stefan
  Atmospheric Environment (2016), 141 (), 542-551CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  Diesel NOx emissions have been at the forefront of research and regulation scrutiny as a result of failures of late vehicle technologies to deliver on-road emissions redns. The current study aims at identifying the actual emissions levels of late light duty vehicle technologies, including Euro 5 and Euro 6 ones. Mean NOx emission factor levels used in the most popular EU vehicle emission models (COPERT, HBEFA and VERSIT+) are compared with latest emission information collected in the lab. over real-world driving cycles and on the road using portable emissions measurement systems (PEMS). The comparison shows that Euro 5 passenger car (PC) emission factors well reflect on road levels and that recently revealed emissions control failures do not call for any significant corrections. However Euro 5 light com. vehicles (LCVs) and Euro 6 PCs in the 2014-2016 period exhibit on road emission levels twice as high as used in current models. Moreover, measured levels vary a lot for Euro 6 vehicles. Scenarios for future evolution of Euro 6 emission factors, reflecting different degree of effectiveness of emissions control regulations, show that total NOx emissions from diesel Euro 6 PC and LCV may correspond from 49% up to 83% of total road transport emissions in 2050. Unless upcoming and long term regulations make sure that light duty diesel NOx emissions are effectively addressed, this will have significant implications in meeting future air quality and national emissions ceilings targets.
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12. 12
  Department for Transport, Vehicle Emissions Testing Programme. 2016; https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/548148/vehicle-emissions-testing-programme-web.pdf, (accessed May 14, 2019).
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13. 13
  Baldino, C.; Tietge, U.; Muncrief, R.; Bernard, Y.; Mock, P. Road Tested: Comparative Overview of Real-world Versus Type-approval NO_x and CO₂ Emissions from Diesel Cars in Europe. 2017; https://www.theicct.org/sites/default/files/publications/ICCT_RoadTested_201709.pdf, International Council on Clean Transportation Europe (accessed May 14, 2019).
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14. 14
  Degraeuwe, B.; Weiss, M. Does the New European Driving Cycle (NEDC) really fail to capture the NO_x emissions of diesel cars in Europe?. Environ. Pollut. 2017, 222, 234– 241, DOI: 10.1016/j.envpol.2016.12.050
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  14
  Does the New European Driving Cycle (NEDC) really fail to capture the NOX emissions of diesel cars in Europe?
  Degraeuwe, Bart; Weiss, Martin
  Environmental Pollution (Oxford, United Kingdom) (2017), 222 (), 234-241CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
  Tests with Portable Emissions Measurement Systems (PEMS) have demonstrated that diesel cars emit several times more NOX on the road than during certification on the New European Driving Cycle (NEDC). Policy makers and scientists have attributed the discrepancy to the unrealistically low dynamics and the narrow temp. range of NEDC testing. Although widely accepted, this assumption was never been put under scientific scrutiny. Here, we demonstrate that the narrow NEDC test conditions explain only a small part of the elevated on-road NOX emissions of diesel cars. For seven Euro 4-6 diesel cars, we filter from on-road driving those events that match the NEDC conditions in instantaneous speed, acceleration, CO2 emissions, and ambient temp. The resulting on-road NOX emissions exceed by 206% (median) those measured on the NEDC, whereas the NOX emissions of all unfiltered on-road measurements exceed the NEDC emissions by 266% (median). Moreover, when applying the same filtering of on-road data to two other driving cycles (WLTP and CADC), the resulting on-road NOX emissions exceed by only 13% (median) those measured over the resp. cycles. This result demonstrates that our filtering method is accurate and robust. If neither the low dynamics nor the limited temp. range of NEDC testing can explain the elevated NOX emissions of diesel cars, emissions control strategies used during NEDC testing must be inactive or modulated on the road, even if vehicles are driven under certification-like conditions. This points to defeat strategies that warrant further investigations by type-approval authorities and, in turn, limitations in the enforcement of the European vehicle emissions legislation by EU Member States. We suggest applying our method as a simple yet effective tool to screen and select vehicles for in-depth anal. by the competent certification authorities.
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15. 15
  O’Driscoll, R.; Stettler, M. E. J.; Molden, N.; Oxley, T.; ApSimon, H. M. Real world CO₂ and NO_x emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars. Sci. Total Environ. 2018, 621, 282– 290, DOI: 10.1016/j.scitotenv.2017.11.271
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  15
  Real world CO2 and NOx emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars
  O'Driscoll, Rosalind; Stettler, Marc E. J.; Molden, Nick; Oxley, Tim; Ap Simon, Helen M.
  Science of the Total Environment (2018), 621 (), 282-290CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
  In this study CO2 and NOx emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars were compared using a Portable Emissions Measurement System (PEMS). The models sampled accounted for 56% of all passenger cars sold in Europe in 2016. We found gasoline vehicles had CO2 emissions 13-66% higher than diesel. During urban driving, the av. CO2 emission factor was 210.5 (sd. 47) g km- 1 for gasoline and 170.2 (sd. 34) g km- 1 for diesel. Half the gasoline vehicles tested were Gasoline Direct Injection (GDI). Euro 6 GDI engines < 1.4l delivered ∼ 17% CO2 redn. compared to Port Fuel Injection (PFI). Gasoline vehicles delivered an 86-96% redn. in NOx emissions compared to diesel cars. The av. urban NOx emission from Euro 6 diesel vehicles 0.44 (sd. 0.44) g km- 1 was 11 times higher than for gasoline 0.04 (sd. 0.04) g km- 1. We also analyzed two gasoline-elec. hybrids which out-performed both gasoline and diesel for NOx and CO2. We conclude action is required to mitigate the public health risk created by excessive NOx emissions from modern diesel vehicles. Replacing diesel with gasoline would incur a substantial CO2 penalty, however greater uptake of hybrid vehicles would likely reduce both CO2 and NOx emissions. Discrimination of vehicles on the basis of Euro std. is arbitrary and incentives should promote vehicles with the lowest real-world emissions of both NOx and CO2.
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16. 16
  Lewis, A. C.; Carslaw, D. C.; Kelly, F. J. Diesel pollution long under-reported. Nature 2015, 526, 195, DOI: 10.1038/526195c
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  Vehicle emissions Diesel pollution long under-reported
  Lewis, Alastair C.; Carslaw, David C.; Kelly, Frank J.
  Nature (London, United Kingdom) (2015), 526 (7572), 195CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  The furor over Volkswagen cheating of US emission tests (ibid., 2015) prompts a reminder that pollution (NOx, hydrocarbons, particulate matter) from diesel-fueled vehicles has long been under-reported. Modern diesel engines emit roughly 4 times more NOx on av. than that recorded in lab. tests which use unrepresentative driving cycles and tech. strategies to reduce emissions. Actual diesel hydrocarbon emissions exceed ests. used for air quality planning by up to 70 times (R.E. Dunmore, et al., 2015). Improved air quality in many European cities stalled 10 years ago; NOx often exceed regulatory stds. and global health guidelines. To tighten up diesel emissions control, tests must be more accurate, transparent, and more vigorously regulated.
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  https://doi.org/10.1038/526195c
17. 17
  Transport Environment, #Dieselgate continues: new cheating techniques. 2016; https://www.transportenvironment.org/sites/te/files/publications/2016_05_Dieselgate_continues_briefing.pdf (accessed May 14, 2019).
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18. 18
  Keller, M.; Hausberger, S.; Matzer, C.; Wüthrich, P.; Notter, B. A novel approach for NOx emission factors of diesel cars in HBEFA (Version 3.3). 2017; 22nd International Transport and Air Pollution Conference, 15–16 November 2017, Zürich, Switzerland.
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19. 19
  Keller, M.; Hausberger, S.; Matzer, C.; Wüthrich, P. Handbook emission factors for road transport-HBEFA Version 3.3. 2017; http://www.hbefa.net/e/documents/HBEFA33_Documentation_20170425.pdf, Background documentation. ″Quick update″ (accessed May 14, 2019).
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20. 20
  Borken-Kleefeld, J.; Dallmann, T. Remote Sensing of Motor Vehicle Exhaust Emissions. 2018; https://theicct.org/publications/vehicle-emission-remote-sensing, International Council on Clean Transportation. White Paper (accessed May 14, 2019).
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21. 21
  Suarez-Bertoa, R.; Astorga, C. Impact of cold temperature on Euro 6 passenger car emissions. Environ. Pollut. 2018, 234, 318– 329, DOI: 10.1016/j.envpol.2017.10.096
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  21
  Impact of cold temperature on Euro 6 passenger car emissions
  Suarez-Bertoa, Ricardo; Astorga, Covadonga
  Environmental Pollution (Oxford, United Kingdom) (2018), 234 (), 318-329CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
  Hydrocarbons and particulate matter emissions affect air quality, global warming and human health. Transport sector is an important source of these pollutants and high pollution episodes are often experienced during the cold season. However, EU vehicle emissions regulation at cold ambient temp. only addresses hydrocarbons and CO vehicular emissions. For that reason, we have studied the impact that cold ambient temps. have on Euro 6 diesel and spark ignition vehicle emissions using the World-harmonized Light-duty Test Cycle (WLTC) at -7°C and 23°C. Results indicate that when facing the WLTC at 23°C the tested vehicles present emissions below the values set for type approval of Euro 6 vehicles, with the exception of NOx emissions from diesel vehicles that were 2.3-6 times higher than Euro 6 stds. However, emissions disproportionally increased when vehicles were tested at cold ambient temp. (-7°C). High solid particle no. (SPN) emissions were measured from gasoline direct injection (GDI) vehicles and gasoline port fuel injection vehicles. However, only diesel and GDI SPN emissions are currently regulated. Results show the need for a new, technol. independent, procedure that enables the authorities to assess pollutant emissions from vehicles at cold ambient temps. Harmful pollutant emissions from spark ignition and diesel vehicles are strongly and neg. affected by cold ambient temps. Only hydrocarbon, CO emissions are currently regulated at cold temp.
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22. 22
  Suarez-Bertoa, R.; Kousoulidou, M.; Clairotte, M.; Giechaskiel, B.; Nuottimäki, J.; Sarjovaara, T.; Lonza, L. Impact of HVO blends on modern diesel passenger cars emissions during real world operation. Fuel 2019, 235, 1427– 1435, DOI: 10.1016/j.fuel.2018.08.031
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  22
  Impact of HVO blends on modern diesel passenger cars emissions during real world operation
  Suarez-Bertoa, Ricardo; Kousoulidou, Marina; Clairotte, Michael; Giechaskiel, Barouch; Nuottimaki, Jukka; Sarjovaara, Teemu; Lonza, Laura
  Fuel (2019), 235 (), 1427-1435CODEN: FUELAC; ISSN:0016-2361. (Elsevier Ltd.)
  Regulated and unregulated emissions from two Euro 6b diesel passenger cars tested using three different blends of hydrotreated vegetable oil (HVO), fossil diesel and com. diesel (B7) were investigated at 23 °C and -7 °C using the World harmonized Light-duty vehicle Test Procedure at the Vehicle Emission Lab. of the European Commission Joint Research Center Ispra, Italy. The HVO blends used were: Neat HVO (100 vol% HVO), 30 vol% HVO and 7 vol% HVO. One of the vehicles was also tested using the three HVO blends on-road following a RDE compliant route. Overall, the use of different HVO blends and diesel did not lead to fuel related trends on the emissions of the tested vehicles in the lab. nor on-road. However, HVO-100 resulted in ∼4% lower CO2 emissions than the other fuel tested in all the studied conditions. Low ambient temp. caused an increase of the emissions of studied compds. (with the exception of NH3) with all tested blends. The exptl. results showed that in many cases the obsd. outcomes were probably attributable to a combination of combustion effects, after-treatment effects, and their control strategy.
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23. 23
  Cha, J.; Lee, J.; Chon, M. S. Evaluation of real driving emissions for Euro 6 light-duty diesel vehicles equipped with LNT and SCR on domestic sales in Korea. Atmos. Environ. 2019, 196, 133– 142, DOI: 10.1016/j.atmosenv.2018.09.029
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  23
  Evaluation of real driving emissions for Euro 6 light-duty diesel vehicles equipped with LNT and SCR on domestic sales in Korea
  Cha, Junepyo; Lee, Jongtae; Chon, Mun Soo
  Atmospheric Environment (2019), 196 (), 133-142CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  In general, recent certification procedure for regulatory emission limits is used to the std. test cycles in the lab. under standardized operating conditions. But, it is proving that the real driving emissions (RDE) of vehicles highly exceed the std. emission limits. In order to tackle this problem, RDE regulation has been proposed with the Potable Emissions Measurement Systems (PEMS). In present study, the PEMS (Portable Emissions Measurement System) equipment, which consists of an exhaust gas flow meter, an exhaust gas sampling device, an exhaust gas analyzer, an OBD data acquisition device, GPS and ambient air sensors, and power supplying device, is installed on 17 test vehicles (Euro 6) sold in Korea currently. And two test driving routes (Route A and B) under 3rd RDE package were developed to include Seoul into urban driving due to reflecting representative traffic and road conditions in Korea. In results, the av. NOx emissions of most test vehicles approx. exceeded 6.6 times the emission limit on test routes. Addnl., the on-road NOx emissions of test vehicles by applying SCR during the same trip were not relatively different based on the ambient temps. With respect to most test vehicles, the CO2 emissions in the urban section are generally higher than those in the total trip.
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24. 24
  Ko, J.; Myung, C.-L.; Park, S. Impacts of ambient temperature, DPF regeneration, and traffic congestion on NO_x emissions from a Euro 6-compliant diesel vehicle equipped with an LNT under real-world driving conditions. Atmos. Environ. 2019, 200, 1– 14, DOI: 10.1016/j.atmosenv.2018.11.029
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  24
  Impacts of ambient temperature, DPF regeneration, and traffic congestion on NOx emissions from a Euro 6-compliant diesel vehicle equipped with an LNT under real-world driving conditions
  Ko, Jinyoung; Myung, Cha-Lee; Park, Simsoo
  Atmospheric Environment (2019), 200 (), 1-14CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  A real driving emissions test procedure was introduced as a supplement to the chassis dynamometer test to diminish the discrepancy between on-road emissions and type approval certification emissions. In this study, on-road NOx emissions from a 2.2 L diesel vehicle equipped with a lean NOx trap were measured not by a portable emissions measurement system but by NOx sensors and an exhaust flow meter. This method provides a strategy for analyzing on-road NOx emissions with a measurement system that is relatively cheap, light and simple. The effects of ambient temp., diesel particulate filter regeneration, traffic congestion, NOx conversion efficiency and uphill/downhill sections on NOx emissions were evaluated by comparing the NOx emissions characteristics using engine-out and lean NOx trap-out NOx sensors. NOx emissions in congested traffic conditions were 29% higher than those in smooth traffic conditions. NOx emissions at 33 °C were 55% higher than those at 27 °C. Addnl., NOx emissions under specific conditions with diesel particulate filter regeneration were 30% higher than those under normal conditions. The av. on-road NOx emission factor for all test cases was 7.35, but this value decreased to 5.7 when an ambient temp. corrective factor (1.6) was applied for extended test conditions.
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25. 25
  Weilenmann, M.; Favez, J.-Y.; Alvarez, R. Cold-start emissions of modern passenger cars at different low ambient temperatures and their evolution over vehicle legislation categories. Atmos. Environ. 2009, 43, 2419– 2429, DOI: 10.1016/j.atmosenv.2009.02.005
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  Cold-start emissions of modern passenger cars at different low ambient temperatures and their evolution over vehicle legislation categories
  Weilenmann, Martin; Favez, Jean-Yves; Alvarez, Robert
  Atmospheric Environment (2009), 43 (15), 2419-2429CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  The emissions of modern gasoline and diesel passenger cars are reduced by catalysts except in cold-starting. Since catalysts require a certain temp. (typically above 300 °C) to work to full efficiency, emissions are significantly higher during the warm-up phase of the car. The duration of this period and the emissions produced depend on the ambient temp. as well as on the initial temp. of the car's propulsion systems. The addnl. emissions during a warm-up phase, known as "cold-start extra emissions" (CSEEs) for emission inventory modeling, are mostly assessed by emission measurements at an ambient temp. of 23 °C. However, in many European countries av. ambient temps. are below 23 °C. This necessitates emission measurements at lower temps. in order to model and assess cold-start emissions for real-world temp. conditions. This paper investigates the influence of regulated pollutants and CO2 emissions of recent gasoline and diesel car models (Euro-4 legislation) at different ambient temps., 23, -7 and -20 °C. We present a survey and model of the evolution of cold-start emissions as a function of different car generations (pre-Euro-1 to Euro-4 legislations). In addn. the contribution of CSEEs to total fleet running emissions is shown to highlight their increasing importance. For gasoline cars, it turns out that in av. real-world driving the majority of the CO (carbon monoxide) and HC (hydrocarbon) total emissions are due to cold-start extra emissions. Moreover, the cold-start emissions increase considerably at lower ambient temps. In contrast, cold-start emissions of diesel cars are significantly lower than those of gasoline cars. Furthermore, the transition from Euro-3 to Euro-4 gasoline vehicles shows a trend for a smaller decline for cold-start extra emissions than for legislative limits. Particle and NOx emission of cold-starts are less significant.
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26. 26
  Roberts, A.; Brooks, R.; Shipway, P. Internal combustion engine cold-start efficiency: A review of the problem, causes and potential solutions. Energy Convers. Manage. 2014, 82, 327– 350, DOI: 10.1016/j.enconman.2014.03.002
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27. 27
  Carslaw, D. C.; Murrells, T. P.; Andersson, J.; Keenan, M. Have vehicle emissions of primary NO₂ peaked?. Faraday Discuss. 2016, 189, 439– 454, DOI: 10.1039/C5FD00162E
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  Have vehicle emissions of primary NO2 peaked?
  Carslaw, David C.; Murrells, Tim P.; Andersson, Jon; Keenan, Matthew
  Faraday Discussions (2016), 189 (Chemistry in the Urban Atmosphere), 439-454CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)
  Reducing ambient concns. of nitrogen dioxide (NO2) remains a key challenge across many European urban areas, particularly close to roads. This challenge mostly relates to the lack of redn. in emissions of oxides of nitrogen (NOx) from diesel road vehicles relative to the redns. expected through increasingly stringent vehicle emissions legislation. However, a key component of near-road concns. of NO2 derives from directly emitted (primary) NO2 from diesel vehicles. It is well-established that the proportion of NO2 (i.e. the NO2/NOx ratio) in vehicle exhaust has increased over the past decade as a result of vehicle after-treatment technologies that oxidise carbon monoxide and hydrocarbons and generate NO2 to aid the emissions control of diesel particulate. In this work we bring together an anal. of ambient NOx and NO2 measurements with comprehensive vehicle emission remote sensing data obtained in London to better understand recent trends in the NO2/NOx ratio from road vehicles. We show that there is evidence that NO2 concns. have decreased since around 2010 despite less evidence of a redn. in total NOx. The decrease is shown to be driven by relatively large redns. in the amt. of NO2 directly emitted by vehicles; from around 25 vol% in 2010 to 15 vol% in 2014 in inner London, for example. The anal. of NOx and NO2 vehicle emission remote sensing data shows that these redns. have been mostly driven by reduced NO2/NOx emission ratios from heavy duty vehicles and buses rather than light duty vehicles. However, there is also evidence from the anal. of Euro 4 and 5 diesel passenger cars that as vehicles age the NO2/NOx ratio decreases. For example the NO2/NOx ratio decreased from 29.5 ± 2.0% in Euro 5 diesel cars up to one year old to 22.7 ± 2.5% for four-year old vehicles. At some roadside locations the redns. in primary NO2 have had a large effect on reducing both the annual mean and no. of hourly exceedances of the European Limit Values of NO2.
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28. 28
  Myung, C.-L.; Jang, W.; Kwon, S.; Ko, J.; Jin, D.; Park, S. Evaluation of the real-time de-NO_x performance characteristics of a LNT-equipped Euro-6 diesel passenger car with various vehicle emissions certification cycles. Energy 2017, 132, 356– 369, DOI: 10.1016/j.energy.2017.05.089
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  Evaluation of the real-time de-NOx performance characteristics of a LNT-equipped Euro-6 diesel passenger car with various vehicle emissions certification cycles
  Myung, Cha-Lee; Jang, Wonwook; Kwon, Sangil; Ko, Jinyoung; Jin, Dongyoung; Park, Simsoo
  Energy (Oxford, United Kingdom) (2017), 132 (), 356-369CODEN: ENEYDS; ISSN:0360-5442. (Elsevier Ltd.)
  Advanced nitrogen oxides (NOx) after-treatment systems for diesel cars are effectively reducing tailpipe NOx emissions in lab. test cycles; however, some de-NOx systems showed limitation for passing environmental stds. during real-world driving conditions. In this study, the NOx concn. of a lean NOx trap (LNT)-equipped diesel engine were investigated over various vehicle certification cycles. The LNT performance was compared to the new European driving cycle (NEDC), world-harmonized light-duty vehicle test cycle (WLTC), federal test procedure (FTP)-75, highway fuel economy test (HWFET), and US06. The real-time NOx concn. behaviors were tracked using NOx sensors at the engine-out and downstream of the LNT to det. the NOx storage and regeneration phase. The NOx conversion efficiencies were 36.3-71.7% of which reflecting the mode severity and cycle duration of the diesel engine. The tailpipe NOx emissions were 0.059 g/km during the NEDC which was within the Euro-6 emissions regulations. The NOx emissions in the WLTC, FTP-75, and US06 modes were approx. 1.9, 1.5, and 6.6 times higher than the NEDC due to the higher frequency of LNT purge and higher engine-out NOx formation. During the diesel particulate filter (DPF) regenerating stage in WLTC mode, tailpipe NOx emissions substantially increased by more than 8.8-fold. The exhaust gas recirculation (EGR) supply and lambda control scheme were closely related with strong NOx increment at de-NOx and de-PM processes.
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29. 29
  Lindhjem, C.; Chan, L.-M.; Pollack, A.; Kite, C. Applying Humidity and Temperature Corrections to On and Off-Road Mobile Source Emissions. 2004; https://www3.epa.gov/ttnchie1/conference/ei13/mobile/lindhjem.pdf, (accessed May 14, 2019).
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30. 30
  Rakopoulos, C. D. Ambient temperature and humidity effects on the performance and nitric oxide emission of spark ignition engined vehicles in Athens/Greece. Solar & Wind Technology 1988, 5, 315– 320, DOI: 10.1016/0741-983X(88)90031-8
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  Chang, Y.; Mendrea, B.; Sterniak, J.; Bohac, S. V. Effect of Ambient Temperature and Humidity on Combustion and Emissions of a Spark-Assisted Compression Ignition Engine. J. Eng. Gas Turbines Power 2017, 139, 051501– 051501–7, DOI: 10.1115/1.4034966
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  Effect of ambient temperature and humidity on combustion and emissions of a spark-assisted compression ignition engine
  Chang, Yan; Mendrea, Brandon; Sterniak, Jeff; Bohac, Stanislav V.
  Journal of Engineering for Gas Turbines and Power (2017), 139 (5), 051501/1-051501/7CODEN: JETPEZ; ISSN:1528-8919. (American Society of Mechanical Engineers)
  Spark-assisted compression ignition (SACI) offers more practical combustion phasing control and a lower pressure rise rate than homogeneous charge compression ignition (HCCI) combustion and improved thermal efciency and lower NOx emissions than spark ignition (SI) combustion. Any practical passenger car engine, including one that uses SACI in part of its operating range, must be robust to changes in ambient conditions. This study investigates the effects of ambient temp. and humidity on stoichiometric SACI combustion and emissions. It is shown that at the medium speed and load SACI test point selected for this study, increasing ambient air temp. from 20°C to 41 #x00B0;C advances combustion phasing, increases max. pressure rise rate, causes a larger fraction of the charge to be consumed by auto-ignition (and a smaller fraction by ame propagation), and increases NOx. Increasing ambient humidity from 32% to 60% retards combustion phasing, reduces max. pressure rise rate, increases coefcient of variation (COV) of indicated mean effective pressure (IMEP), reduces NOx, and increases brake-specic fuel consumption (BSFC). These results show that successful implementation of SACI combustion in real-world driving requires a control strategy that compensates for changes in ambient temp. and humidity.
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32. 32
  U.S. Environmental Protection Agency, Emission Adjustments for Temperature, Humidity, Air Conditioning, and Inspection and Maintenance for On-road Vehicles in MOVES2014. 2014; Assessment and Standards Division Office of Transportation and Air Quality U.S. Environmental Protection Agency. EPA-420-R-14–012. December 2014 (accessed May 14, 2019).
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  U.S. Environmental Protection Agency, Derivation of Humidty and NO_x Humidty Correction Factors. 2016; https://www.epa.gov/sites/production/files/2015-09/documents/noxcorr.pdf, US-EPA-OAR-OMS-TSD (accessed May 14, 2019).
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  Air pollution in cities
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  Atmospheric Environment (1999), 33 (24-25), 4029-4037CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science Ltd.)
  The review with 24 refs. Air quality in cities is the result of a complex interaction between natural and anthropogenic environmental conditions. Air pollution in cities is a serious environmental problem - esp. in the developing countries. The air pollution path of the urban atm. consists of emission and transmission of air pollutants resulting in the ambient air pollution. Each part of the path is influenced by different factors. Emissions from motor traffic are a very important source group throughout the world. During transmission, air pollutants are dispersed, dild. and subjected to photochem. reactions. Ambient air pollution shows temporal and spatial variability. As an example of the temporal variability of urban air pollutants caused by motor traffic, typical av. annual, weekly and diurnal cycles of Nitric oxide, NO2, O3 and Ox are presented for an official urban air-quality station in Stuttgart, southern Germany. They are supplemented by weekly and diurnal cycles of selected percentile values of NO, NO2, and O3. Time series of these air pollutants give information on their trends. Results are discussed with regard to air pollution conditions in other cities. Possibilities for the assessment of air pollution in cities are shown. In addn., a qual. overview of the air quality of the world's megacities is given.
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  Air pollution in the last 50 years - From local to global
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  Atmospheric Environment (2008), 43 (1), 13-22CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  A review. Air pollution in the industrialized world has in the last 50 years undergone drastic changes. Until after World War II the most important urban compd. was SO2 combined with soot from the use of fossil fuels in heat and power prodn. When that problem was partly solved by cleaner fuels, higher stacks, and flue gas cleaning in urban areas, the growing traffic gave rise to NOx and volatile org. compds. and in some areas photochem. air pollution, which may be abated by catalytic converters. Lately the interest has centered on small particles and more exotic org. compds. that can be detected with new sophisticated anal. techniques. Simultaneously with the development in compds., the time and geog. scale of interest have increased. First to transboundary air pollution, which in decades and on continents can degrade ecosystems, later to the depletion of the ozone layer and esp. to the increasing greenhouse effect with climate change that will change the conditions for nature and mankind on the entire globe. The possibilities to study these large scale phenomena were greatly enhanced by the development of electronic computers that can handle large data sets and calc. various scenarios. All these processes take place in the thin layer of gases around the Earth, the atm. Although the abatement is often restricted to a single aspect, they are often connected and should when possible be treated as whole.
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36. 36
  Scott, A. J.; Scarrott, C. Impacts of residential heating intervention measures on air quality and progress towards targets in Christchurch and Timaru, New Zealand. Atmos. Environ. 2011, 45, 2972– 2980, DOI: 10.1016/j.atmosenv.2010.09.008
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  Impacts of residential heating intervention measures on air quality and progress towards targets in Christchurch and Timaru, New Zealand
  Scott, Angelique J.; Scarrott, Carl
  Atmospheric Environment (2011), 45 (17), 2972-2980CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  Elevated wintertime particulate concns. in the New Zealand cities of Christchurch and Timaru are mostly attributed to the burning of wood and coal for residential heating. A carrot-and-stick approach was adopted for managing air quality in Christchurch, where strict intervention measures were introduced together with a residential heater replacement program to encourage householders to change to cleaner forms of heating. A similar approach was only recently implemented for Timaru. This paper presents the results of a partial accountability anal., where the impact of these measures on the target source, PM10 emissions, and PM10 concns. are quantified. A statistical model was developed to est. trends in the concns., which were tested for significance after accounting for meteorol. effects, and to est. the probability of meeting air quality targets. Results for Christchurch and Timaru are compared to illustrate the impacts of differing levels of intervention on air quality. In Christchurch, approx. 34,000 (76%) open fires and old solid fuel burners were replaced with cleaner heating technol. from 2002 to 2009, and total open fires and solid fuel burner nos. decreased by 45%. Over the same time period, estd. PM10 emissions reduced by 71% and PM10 concns. by 52% (maxima), 36% (winter mean), 26% (winter median) and 41% (meteorol.-adjusted winter means). In Timaru, just 3000 (50%) open fires and old solid fuel burners were replaced from 2001 to 2008, with total open fire and solid fuel burner nos. reduced by 24%. PM10 emissions declined by 32%, with low redns. in the PM10 concns. (maxima decreased by 7%, winter means by 11% and winter medians by 3%). These findings, supported by the results of the meteorol. cor. trend anal. for Christchurch, strongly indicate that the combination of stringent intervention measures and financial incentives has led to substantial air quality improvements in the city. The lesser impact of more lenient rules and the late introduction of an incentives program are obvious on air quality in Timaru. Trends established for the two cities were extrapolated under various scenarios to det. the likelihood of meeting air quality targets. In Christchurch the probability of compliance is low and is essentially impossible for Timaru if recent trends continue.
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37. 37
  Grange, S. K.; Salmond, J. A.; Trompetter, W. J.; Davy, P. K.; Ancelet, T. Effect of atmospheric stability on the impact of domestic wood combustion to air quality of a small urban township in winter. Atmos. Environ. 2013, 70, 28– 38, DOI: 10.1016/j.atmosenv.2012.12.047
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  Effect of atmospheric stability on the impact of domestic wood combustion to air quality of a small urban township in winter
  Grange, S. K.; Salmond, J. A.; Trompetter, W. J.; Davy, P. K.; Ancelet, T.
  Atmospheric Environment (2013), 70 (), 28-38CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  In the winter of 2011, a field campaign was undertaken in the small township of Nelson, New Zealand to measure the vertical and horizontal distribution of concns. of airborne particulate matter. The aim was to improve our understanding of the causal factors which result in periods of very high concns. of particulate pollution in small townships during winter where emissions are dominated by the combustion of wood for domestic heating. The results showed that mean hourly surface concns. of particulates throughout the airshed were characterized by a distinctive diurnal cycle, with 2 peaks in concn. (one in the late evening and then, unusually, a 2nd mid-morning). Although the timing and magnitude of hourly peak concns. was variable throughout the valley, there was no evidence to suggest that regional or topog. flows played a significant role in the build-up of pollutants at any given location. Anal. of vertical profiles of black C showed that high concns. of particulates were confined to the lowest 50 m of the boundary layer. Concns. decreased with increasing height within this polluted surface layer. The atmosphere was very stable during the evening period. After midnight, a period of increased mixing was consistently identified throughout the lowest 100 m of the boundary layer and assocd. with the sudden cleansing of the surface and lower layers of the boundary layer. Throughout the observational period there was no evidence for the storage of pollutants aloft. Thus the vertical mixing of pollutants to the surface could not account for increased pollutant concns. during the morning period. However, at this time the boundary layer remained stable and concns. of black carbon were mixed through a very shallow layer. This suggests that despite lower domestic heating emissions in the morning, the reduced mixing vol. is a likely cause of the obsd. marked peak in morning surface concns.
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38. 38
  Anenberg, S. C.; Miller, J.; Minjares, R.; Du, L.; Henze, D. K.; Lacey, F.; Malley, C. S.; Emberson, L.; Franco, V.; Klimont, Z.; Heyes, C. Impacts and mitigation of excess diesel-related NO_x emissions in 11 major vehicle markets. Nature 2017, 545, 467– 471, DOI: 10.1038/nature22086
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  Impacts and mitigation of excess diesel-related NOx emissions in 11 major vehicle markets
  Anenberg, Susan C.; Miller, Joshua; Minjares, Ray; Du, Li; Henze, Daven K.; Lacey, Forrest; Malley, Christopher S.; Emberson, Lisa; Franco, Vicente; Klimont, Zbigniew; Heyes, Chris
  Nature (London, United Kingdom) (2017), 545 (7655), 467-471CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  Vehicle emissions contribute to fine particulate matter (PM2.5) and tropospheric O3 air pollution, affecting human health, crop yields, and climate worldwide. On-road diesel vehicles produce ∼20% of global anthropogenic NOx emissions, which are key PM2.5 and O3 precursors. Regulated NOx emission limits in leading markets have progressively tightened, but current diesel vehicles emit far more NOx under actual operating conditions vs. lab. certification testing. This work showed that across 11 markets representing ∼80% of global diesel vehicle sales, nearly one-third of on-road heavy-duty diesel vehicle emissions and more than half the on-road light-duty diesel vehicle emissions are in excess of certification limits. These excess emissions (totaling 4.6 million tons) are assocd. with ∼38,000 PM2.5- and O3-related premature deaths globally in 2015, including ∼10% of all O3-related premature deaths in the 28 European Union member states. Heavy-duty vehicles are the dominant contributor to excess diesel NOx emissions and assocd. health impacts in nearly all regions. Adopting and enforcing next-generation stds. (more stringent than Euro 6/VI) could nearly eliminate actual diesel-related NOx emissions in these markets, avoiding ∼174,000 global PM2.5- and O3-related premature deaths in 2040. Most of these benefits can be achieved by implementing Euro VI stds. where they have not yet been adopted for heavy-duty vehicles.
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  Chossière, G. P.; Malina, R.; Ashok, A.; Dedoussi, I. C.; Eastham, S. D.; Speth, R. L.; Barrett, S. R. H. Public health impacts of excess NO_x emissions from Volkswagen diesel passenger vehicles in Germany. Environ. Res. Lett. 2017, 12, 034014, DOI: 10.1088/1748-9326/aa5987
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  Public health impacts of excess NOx emissions from Volkswagen diesel passenger vehicles in Germany
  Chossiere, Guillaume P.; Malina, Robert; Ashok, Akshay; Dedoussi, Irene C.; Eastham, Sebastian D.; Speth, Raymond L.; Barrett, Steven R. H.
  Environmental Research Letters (2017), 12 (3), 034014/1-034014/14CODEN: ERLNAL; ISSN:1748-9326. (IOP Publishing Ltd.)
  In Sept. 2015, the Volkswagen Group (VW) admitted the use of 'defeat devices' designed to lower emissions measured during VW vehicle testing for regulatory purposes. Globally, 11 million cars sold between 2008 and 2015 are affected, including about 2.6 million in Germany. On-road emissions tests have yielded mean on-road NOx emissions for these cars of 0.85 g km-1, over four times the applicable European limit of 0.18 g km-1. This study ests. the human health impacts and costs assocd. with excess emissions from VW cars driven in Germany. A distribution of on-road emissions factors is derived from existing measurements and combined with sales data and a vehicle fleet model to est. total excess NOx emissions. These emissions are distributed on a 25 by 28 km grid covering Europe, using the German Environmental Protection Agency's (UBA) est. of the spatial distribution of NOx emissions from passenger cars in Germany. We use the GEOS-Chem chem.-transport model to predict the corresponding increase in population exposure to fine particulate matter and ozone in the European Union, Switzerland, and Norway, and a set of concn.-response functions to est. mortality outcomes in terms of early deaths and of life-years lost. Integrated over the sales period (2008-2015), we est. median mortality impacts from VW excess emissions in Germany to be 1 200 premature deaths in Europe, corresponding to 13 000 life-years lost and 1.9 billion EUR in costs assocd. with life-years lost. Approx. 60% of mortality costs occur outside Germany. For the current fleet, we est. that if on-road emissions for all affected VW vehicles in Germany are reduced to the applicable European emission std. by the end of 2017, this would avert 29 000 life-years lost and 4.1 billion 2015 EUR in health costs (median ests.) relative to a counterfactual case with no recall.
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  Jonson, J. E.; Borken-Kleefeld, J.; Simpson, D.; Nyíri, A.; Posch, M.; Heyes, C. Impact of excess NO_x emissions from diesel cars on air quality, public health and eutrophication in Europe. Environ. Res. Lett. 2017, 12, 094017, DOI: 10.1088/1748-9326/aa8850
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  Impact of excess NOx emissions from diesel cars on air quality, public health and eutrophication in Europe
  Jonson, J. E.; Borken-Kleefeld, J.; Simpson, D.; Nyiri, A.; Posch, M.; Heyes, C.
  Environmental Research Letters (2017), 12 (9), 094017/1-094017/11CODEN: ERLNAL; ISSN:1748-9326. (IOP Publishing Ltd.)
  Diesel cars have been emitting four to seven times more NOx in on-road driving than in type approval tests. These 'excess emissions' are a consequence of deliberate design of the vehicle's after-treatment system, as investigations during the 'Dieselgate' scandal have revealed. Here we calc. health and environmental impacts of these excess NOx emissions in all European countries for the year 2013. We use national emissions reported officially under the UNECE Convention for Long-range Transport of Atm. Pollutants and employ the EMEP MSC-W Chem. Transport Model and the GAINS Integrated Assessment Model to det. atm. concns. and resulting impacts. We compare with impacts from hypothetical emissions where light duty diesel vehicles are assumed to emit only as much as their resp. type approval limit value or as little as petrol cars of the same age. Excess NO2 concns. can also have direct health impacts, but these overlap with the impacts from particulate matter (PM) and are not included here. We est. that almost 10 000 premature deaths from PM2.5 and ozone in the adult population (age>30 years) can be attributed to the NOx emissions from diesel cars and light com. vehicles in EU28 plus Norway and Switzerland in 2013. About 50% of these could have been avoided if diesel limits had been achieved also in on-road driving; and had diesel cars emitted as little NOx as petrol cars, 80% of these premature deaths could have been avoided. Ecosystem eutrophication impacts (crit. load exceedances) from the same diesel vehicles would also have been reduced at similar rates as for the health effects.
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  Measuring the Emissions of Passing Cars
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  An on-road IR remote sensing system to measure exhaust gas emissions from passing automobiles is discussed.
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  Burgard, D. A.; Bishop, G. A.; Stadtmuller, R. S.; Dalton, T. R.; Stedman, D. H. Spectroscopy Applied to On-Road Mobile Source Emissions. Appl. Spectrosc. 2006, 60, 135A– 148A, DOI: 10.1366/000370206777412185
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  Spectroscopy applied to on-road mobile source emissions
  Burgard, Daniel A.; Bishop, Gary A.; Stadtmuller, Ryan S.; Dalton, Thomas R.; Stedman, Donald H.
  Applied Spectroscopy (2006), 60 (5), 135A-148ACODEN: APSPA4; ISSN:0003-7028. (Society for Applied Spectroscopy)
  A review. There have been many advances in both the instrumentation and in the redn. of pollutants since the first reported attempt at remote sensing of on-road vehicle emissions in 1973. The detection of mobile source emissions by means of a remote sensing device is almost entirely an application of absorption spectroscopy. Remote sensing has been able to measure individual vehicle emissions remotely as the vehicle drives by in its normal driving mode. As vehicles continue the trend in reduced emissions of regulated pollutants, remote sensing will continue to adapt to be able to measure new species of concern, in new locations, and with new instrumental arrangements. Remote sensing has provided real-world, in-use, and on-road measurements of millions of vehicles around the world. On a cost per vehicle basis, remote sensing remains the least expensive emission testing method available. Remote sensing can be used for regulatory, enforcement, and repair purposes or simply to inform the public and allow for voluntary action. However used, remote sensing has provided a wealth of data to on-road emissions and will continue to do so until all of the world's vehicles are zero-emitting or non-combusting.
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  Bishop, G. A.; Haugen, M. J. The Story of Ever Diminishing Vehicle Tailpipe Emissions as Observed in the Chicago, Illinois Area. Environ. Sci. Technol. 2018, 52, 7587– 7593, DOI: 10.1021/acs.est.8b00926
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  The Story of Ever Diminishing Vehicle Tailpipe Emissions as Observed in the Chicago, Illinois Area
  Bishop, Gary A.; Haugen, Molly J.
  Environmental Science & Technology (2018), 52 (13), 7587-7593CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
  The University of Denver has collected on-road fuel specific vehicle emissions measurements in the Chicago area since 1989. This nearly 30 yr record illustrates the large redns. in light-duty vehicle tailpipe emissions and the remarkable improvements in emissions control durability to maintain low emissions over increasing periods of time. Since 1989 fuel specific carbon monoxide (CO) emissions have been reduced by an order of magnitude and hydrocarbon (HC) emissions by more than a factor of 20. Nitric oxide (NO) emissions have only been collected since 1997 but have seen redns. of 79%. This has increased the skewness of the emissions distribution where the 2016 fleet's 99th percentile contributes ∼3 times more of the 1990 total for CO and HC emissions. There are signs that these redns. may be leveling out as the emissions durability of Tier 2 vehicles in use today has almost eliminated the emissions redn. benefit of fleet turnover. Since 1997, the av. age of the Chicago on-road fleet has increased 2 model years and the percentage of passenger vehicles has dropped from 71 to 52% of the fleet. Emissions are now so well controlled that the influence of driving mode has been completely eliminated as a factor for fuel specific CO and NO emissions.
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  Rushton, C. E.; Tate, J. E.; Shepherd, S. P.; Carslaw, D. C. Interinstrument comparison of remote-sensing devices and a new method for calculating on-road nitrogen oxides emissions and validation of vehicle-specific power. J. Air Waste Manage. Assoc. 2018, 68, 111– 122, DOI: 10.1080/10962247.2017.1296504
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  Emissions of nitrogen oxides (NOx) by vehicles in real driving environments are only partially understood. This has been brought to the attention of the world with recent revelations of the cheating of the type of approval tests exposed in the dieselgate scandal. Remote-sensing devices offer investigators an opportunity to directly measure in situ real driving emissions of tens of thousands of vehicles. Remote-sensing NO2 measurements are not as widely available as would be desirable. The aim of this study is to improve the ability of investigators to est. the NO2 emissions and to improve the confidence of the total NOx results calcd. from std. remote-sensing device (RSD) measurements. The accuracy of the RSD speed and acceleration module was also validated using state-of-the-art onboard global positioning system (GPS) tracking. Two RSDs used in roadside vehicle emissions surveys were tested side by side under off-carriageway conditions away from transient pollution sources to ascertain the consistency of their measurements. The speed correlation was consistent across the range of measurements at 95% confidence and the acceleration correlation was consistent at 95% confidence intervals for all but the most extreme acceleration cases. VSP was consistent at 95% confidence across all measurements except for those at VSP ≥ 15 kW t-1, which show a small underestimate. The controlled distribution gas nitric oxide measurements follow a normal distribution with 2σ equal to 18.9% of the mean, compared to 15% obsd. during factory calibration indicative of addnl. error introduced into the system. Systematic errors of +84 ppm were obsd. but within the tolerance of the control gas. Interinstrument correlation was performed, with the relationship between the FEAT and the RSD4600 being linear with a gradient of 0.93 and an R2 of 0.85, indicating good correlation. A new method to calc. NOx emissions using fractional NO2 combined with NO measurements made by the RSD4600 was constructed, validated, and shown to be more accurate than previous methods. Implications: Synchronized remote-sensing measurements of NO were taken using two different remote-sensing devices in an off-road study. It was found that the measurements taken by both instruments were well correlated. Fractional NO2 measurements from a prior study, measurable on only one device, were used to create new NOx emission factors for the device that could not be measured by the second device. These ests. were validated against direct measurement of total NOx emission factors and shown to be an improvement on previous methodologies. Validation of vehicle-specific power was performed with good correlation obsd.
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  A fuel-based methodol. for calcg. motor vehicle emission inventories is presented. In the fuel-based method, emission factors are normalized to fuel consumption and expressed as grams of pollutant emitted per gal of gasoline burned. Fleet-av. emission factors are calcd. from the measured on-road emissions of a large, random sample of vehicles. Gasoline use is known at the state level from sales tax data, and may be disaggregated to individual air basins. A fuel-based motor vehicle CO inventory was calcd. for the South Coast Air Basin in California for summer 1991. Emission factors were calcd. from remote sensing measurements of more than 70,000 in-use vehicles. Stabilized exhaust emissions of CO were estd. to be 4400 tons/day for cars and 1500 tons/day for light-duty and medium-duty trucks, with an estd. uncertainty of ±20% for cars and ±30% for trucks. Total motor vehicle CO emissions, including incremental start emissions and emissions from heavy-duty vehicles were estd. to be 7900 tons/day. Fuel-based inventory ests. were greater than those of California's MVEI 7F model by factors of 2.2 for cars and 2.6 for trucks. A draft version of California's MVEI 7G model, which includes increased contributions from high-emitting vehicles and off-cycle emissions, predicted CO emissions which closely matched the fuel-based inventory. An anal. of CO mass emissions as a function of vehicle age revealed that cars and trucks which were ten or more years old were responsible for 58% of stabilized exhaust CO emissions from all cars and trucks.
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- Details of the gas cylinders used for the field calibrations, counts of captured vehicles based on vehicle type, full names of manufacturer groups, number of vehicle captures, mean NO and NO₂ emissions as captured for both RSD instruments, an example of GAM extrapolation behavior, mean annual and wintertime surface air temperatures for Europe, mean monthly absolute humidity for selected European cities, generalized additive models (GAM) of NO_x emissions with and without humidity corrections applied, ambient NO_x concentrations dependence on air temperature, market share of diesel-powered passenger vehicles, and equation used to correct NO_x emissions for ambient humidity (PDF)
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Strong Temperature Dependence for Light-Duty Diesel Vehicle NOx Emissions

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Abstract

Introduction

Materials and Methods

Measurement Locations

Figure 1

Instrumentation

Data

Data Analysis Approach

Emission Prediction

Results and Discussion

Vehicular NOx Emissions and Ambient Temperature

Figure 2

Figure 3

Figure 4

Air Quality Implications

Figure 5

Figure 6

Supporting Information

Terms & Conditions

Author Information

Acknowledgments

References

Cited By

Abstract

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

References

Supporting Information

Supporting Information

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STEP 1:

STEP 2:

Strong Temperature Dependence for Light-Duty Diesel Vehicle NO_x Emissions

Vehicular NO_x Emissions and Ambient Temperature