Chemical Fingerprinting of Biomass Burning Organic Aerosols from Sugar Cane Combustion: Complementary Findings from Field and Laboratory Studies

Agricultural fires are a major source of biomass-burning organic aerosols (BBOAs) with impacts on health, the environment, and climate. In this study, globally relevant BBOA emissions from the combustion of sugar cane in both field and laboratory experiments were analyzed using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry. The derived chemical fingerprints of fresh emissions were evaluated using targeted and nontargeted evaluation approaches. The open-field sugar cane burning experiments revealed the high chemical complexity of combustion emissions, including compounds derived from the pyrolysis of (hemi)cellulose, lignin, and further biomass, such as pyridine and oxime derivatives, methoxyphenols, and methoxybenzenes, as well as triterpenoids. In comparison, laboratory experiments could only partially model the complexity of real combustion events. Our results showed high variability between the conducted field and laboratory experiments, which we, among others, discuss in terms of differences in combustion conditions, fuel composition, and atmospheric processing. We conclude that both field and laboratory studies have their merits and should be applied complementarily. While field studies under real-world conditions are essential to assess the general impact on air quality, climate, and environment, laboratory studies are better suited to investigate specific emissions of different biomass types under controlled conditions.

Table S2: Composition of the graphitized carbon black (GCB) gas phase sampling tubes Table S3: Sampling parameters for collected particulate matter (PM) during the open-field sugarcane burning experiments Table S4: Sampling parameters for collected gas phase during the open-field sugarcane burning experiments Table S5: Column setup for analysis of PM by TD-GC×GC-TOFMS Table S6: GC temperature profile for analysis of PM by TD-GC×GC-TOFMS Table S7: MS parameters for analysis of PM by TD-GC×GC-TOFMS Figure S1: Temperature and flow settings for the OPTIC-4 inlet and cold trap system for analysis of PM by TD-GC×GC-TOFMS Table S8: Data processing parameters for evaluation of TD-GC×GC-TOFMS data with ChromaTOF Tile Table S9: GC temperature profile for gas phase analysis by GC-MS Table S10: MS parameters for gas phase analysis by GC-MS Table S11: Overview of compounds used for the internal and calibration standard mixture for gas phase analysis by GC-MS Figure S2: Photographs of the combustion of sugarcane in the laboratory and in the field experiments Table S12: List key tracer compounds found biomass burning aerosols according to literature, which we used for targeted evaluation of PM Figure S3: GC×GC contour and bubble plots of these targeted key tracer compounds Figure S4: Semi-quantification of particle phase compounds by TD-GC×GC-TOFMS using a 4point calibration of the internal standard compound fluorene-D10 Table S13: List of compounds derived from non-targeted analysis of sugarcane burning emissions in the field experiments Figure S5: Venn diagram of compounds derived from targeted and non-targeted evaluation of sugarcane burning emissions    (GL Sciences, Netherlands), as well as temperature profile of Cryofocus-4 cold trap system (pink) (GL Sciences, Netherlands) for TD-GC×GC-TOFMS analysis.The thermal desorption of the SVOC from a QF filter punch (d=10 mm) occurred through the application of a gradual thermal gradient of 2 °C sec -1 from 40 °C to 300 °C in order to introduce the analytes onto the GC column set.The inlet purge time was 100 sec at a column flow of 1 mL min -1 and a split flow of 100 mL min -1 .The desorption flow rate was 2.6 mL min -1 in spitless mode.Subsequently, the thermally desorbed analytes were cryogenically focused with the cryotrap at −100 °C.Following the thermal desorption, the column flow was reduced to 1 mL min -1 and the split flow increased to 100 mL min -1 .S12), the concentrations (ng m -3 ) were derived from a 4-point calibration using the internal standard compound fluorene-D10.The total ion chromatogram (TIC) area from each respective compound was used.Values were normalized to the corresponding sampling volume and were corrected for the respective dilution factor (field experiments = n.a.(set to 1) and laboratory experiments = 6).Furthermore, the respective effective filter diameter (42 mm) was considered from which a 10 mm punch was used during the measurements.

Figure S 1 :
Figure S 1:Temperature profile (red), column flow (green) and split flow (blue) parameters for OPTIC-4 inlet system (GL Sciences, Netherlands), as well as temperature profile of Cryofocus-4 cold trap system (pink) (GL Sciences, Netherlands) for TD-GC×GC-TOFMS analysis.The thermal desorption of the SVOC from a QF filter punch (d=10 mm) occurred through the application of a gradual thermal gradient of 2 °C sec -1 from 40 °C to 300 °C in order to introduce the analytes onto the GC column set.The inlet purge time was 100 sec at a column flow of 1 mL min -1 and a split flow of 100 mL min -1 .The desorption flow rate was 2.6 mL min -1 in spitless mode.Subsequently, the thermally desorbed analytes were cryogenically focused with the cryotrap at −100 °C.Following the thermal desorption, the column flow was reduced to 1 mL min -1 and the split flow increased to 100 mL min -1 .

Figure S 2 :
Figure S 2: Photographs from a) the batch-wise burning of dried sugarcane leaves during the laboratory experiments and b) the open-field sugarcane burning experiments in South Africa

Figure S 3 :Figure S 4 :
Figure S 3: a) Targeted analysis of 64 marker compounds from biomass burning found in TD-GC×GC-TOFMS measurements of sugarcane burning emissions (compounds are shown in Table S1); b) Classification of referenced compounds in a GCxGC contour plot of sugarcane burning chamber experiments; c) Classification of referenced compounds in a GCxGC contour plot of sugarcane burning field experiments (TIC normalized areas depicted as size of bubbles)

Table S 4
: Sampling parameters for the collected gas phase on GCB adsorber tubes.Prior to sampling, the gas phase adsorber tubes were conditioned under a protective nitrogen atmosphere at 300 °C to remove possible organic contaminants.
Table S 5: Column setup for TD-GC×GC-TOFMS analysis of filter samples.

Table S 6
: Primary GC oven temperature profile for TD-GC×GC-TOFMS analysis of filter samples.The secondary oven was offset by +20 °C relative to the primary oven temperature and the modulator was offset by +15 °C relative to the secondary oven temperature.The modulation time was 3 sec with a hot pulse time of 1.5 sec.

Table S
7:Mass spectrometric parameters for TD-GC×GC-TOFMS analysis of filter samples.

Table S 8
: Data processing parameters for ChromaTOF Tile (Version v.1.2.6.0,LECO,USA) Compounds used for the internal standard (ISTD) and calibration standard mixture for gas phase analysis by GC-MS.The performed quantitation method has been previously published.2, 3 Table S 9: GC oven temperature profile for gas phase analysis by GC-MSTable S 10: Mass spectrometric parameters for gas phase analysis by GC-MSTable S 11:

Table S
12: Key tracers for organic components in BBOA found in literature used for targeted evaluation.

Table S 13:
Compounds derived from the non-targeted analysis with positive fold changes and a significance level of p<0.01.