Web Release Date: June 5,
Gas-Phase and Particle-Phase Organic Compounds Emitted from Motor Vehicle Traffic in a Los Angeles Roadway Tunnel
Received for review October 20, 1997 Revised manuscript received
March 9, 1998 Accepted March 23, 1998 Abstract: The emission rates for 221 vapor-phase, semivolatile, and
particle-phase organic compounds from motor vehicles
plus fine particulate matter mass and some inorganic
particle-phase species are calculated based on measurements
made inside and outside a Los Angeles roadway tunnel in
1993. These emission rates are calculated based on
fuel consumption to remove any uncertainties based on
tunnel dilution rates or air circulation. The results
show
carbon monoxide emissions rates of 130 g L-1 of
gasoline-equivalent fuel burned and volatile organic compound
(VOC) emissions of 9.1 g L-1. These
values are higher than
predicted by the baseline version of California's EMFAC
7G emissions inventory program but are within the
coemission
rate range of 108 ± 25 g L-1 reported by
roadside
remote sensing studies in Los Angeles [Singer, B. C.;
Harley, R. A. J. Air Waste Manage. Assoc. 1996,
46, 581-593]. When the VOC emissions composition in the
tunnel is compared to that of tailpipe emissions source
test data and to the composition of additional unburned
whole gasoline, the tunnel atmosphere is found to be
consistent with a linear combination of these major
contributors over a fairly broad range of about 74-97%
vehicle exhaust depending on the tailpipe profiles used.
Fine
particulate emissions within the tunnel consist largely of
carbonaceous material accompanied by a significant amount
of ammonium nitrate apparently formed by gas-to-particle conversion processes within the tunnel atmosphere.
Certain gas-phase and particulate organic compounds
traditionally thought to be the secondary products of
atmospheric chemical reactions are enriched inside the
tunnel, and from this enrichment, the primary emission
rates
of aromatic alcohols, aliphatic dicarboxylic acids, and
aromatic polycarboxylic acids are calculated. Data on
petroleum biomarkers emissions rates in the tunnel can be
used in the future to estimate primary vehicle exhaust
fine particulate matter concentrations in the urban
atmosphere.
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