The most conventional and abundant tracers of biomass combustion in aerosol particles include potassium and biomarkers derived from thermally altered cellulose/hemicellulose (anhydrosugars) and lignin (methoxyphenols). However, little is known of the role biomass combustion plays as a particulate source of major plant polymers to the atmosphere. Here, concentrations of solvent-extractable anhydrosugars and methoxyphenols are compared to the yields of polymeric lignin oxidation products (LOPs) during a smoke plume event in Houston, Texas. Downwind aerosol samples (PM2.5) were collected surrounding a two-day wildfire in the McFaddin National Wildlife Refuge, 125 km southeast of Houston, which was 12-16 h directly downwind during the peak of the burn. Concentrations of all organic markers, potassium, and calcium increased by a factor of 2-13 within 1-2 days of the start of the fire and dropped to prefire levels 3 days after the peak event. Source signatures of anhydrosugars and methoxyphenols during the peak of the plume were identical to those of grass charcoals collected from the site, confirming the use of charcoals as end-members for source input reconstruction during atmospheric transport. An enrichment factor of 20 in the anhydrosugar to methoxyphenol ratio of aerosols versus charcoals can be explained partially by differences in degradation rate constants between the biomarker groups. LOPs comprised 73-91% of all lignin material in the aerosols, pointing to fires as major sources of primary biogenic aerosol particles in which lignin phenols occur predominantly in polymeric form.

Abstract. Online and offline measurements of ambient particulate matter (PM) near the urban and industrial Houston Ship Channel in Houston, Texas, USA, during May 2015 were utilized to characterize its chemical composition and to evaluate the relative contributions of primary, secondary, biogenic, and anthropogenic sources. Aerosol mass spectrometry (AMS) on nonrefractory PM1 (PM ≤ 1 µm) indicated major contributions from sulfate (averaging 50 % by mass), organic aerosol (OA, 40 %), and ammonium (14 %). Positive matrix factorization (PMF) of AMS data categorized OA on average as 22 % hydrocarbon-like organic aerosol (HOA), 29 % cooking-influenced less-oxidized oxygenated organic aerosol (CI-LO-OOA), and 48 % more-oxidized oxygenated organic aerosol (MO-OOA), with the latter two sources indicative of secondary organic aerosol (SOA). Chemical analysis of PM2.5 (PM ≤ 2.5 µm) filter samples agreed that organic matter (35 %) and sulfate (21 %) were the most abundant components. Organic speciation of PM2.5 organic carbon (OC) focused on molecular markers of primary sources and SOA tracers derived from biogenic and anthropogenic volatile organic compounds (VOCs). The sources of PM2.5 OC were estimated using molecular marker-based positive matric factorization (MM-PMF) and chemical mass balance (CMB) models. MM-PMF resolved nine factors that were identified as diesel engines (11.5 %), gasoline engines (24.3 %), nontailpipe vehicle emissions (11.1 %), ship emissions (2.2 %), cooking (1.0 %), biomass burning (BB, 10.6 %), isoprene SOA (11.0 %), high-NOx anthropogenic SOA (6.6 %), and low-NOx anthropogenic SOA (21.7 %). Using available source profiles, CMB apportioned 41 % of OC to primary fossil sources (gasoline engines, diesel engines, and ship emissions), 5 % to BB, 15 % to SOA (including 7.4 % biogenic and 7.6 % anthropogenic), and 39 % to other sources that were not included in the model and are expected to be secondary. This study presents the first application of in situ AMS-PMF, MM-PMF, and CMB for OC source apportionment and the integration of these methods to evaluate the relative roles of biogenic, anthropogenic, and BB-SOA. The three source apportionment models agreed that ∼ 50 % of OC is associated with primary emissions from fossil fuel use, particularly motor vehicles. Differences among the models reflect their ability to resolve sources based upon the input chemical measurements, with molecular marker-based methods providing greater source specificity and resolution for minor sources. By combining results from MM-PMF and CMB, BB was estimated to contribute 11 % of OC, with 5 % primary emissions and 6 % BB-SOA. SOA was dominantly anthropogenic (28 %) rather than biogenic (11 %) or BB-derived. The three-model approach demonstrates significant contributions of anthropogenic SOA to fine PM. More broadly, the findings and methodologies presented herein can be used to advance local and regional understanding of anthropogenic contributions to SOA.

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We present field observations made in June 2011 downwind of Dallas−Fort Worth, TX, and evaluate the role of stabilized Criegee radicals (sCIs) in gaseous sulfuric acid (H 2 SO 4 ) production. Zerodimensional model calculations show that sCI from biogenic volatile organic compounds composed the majority of the sCIs. The main uncertainty associated with an evaluation of H 2 SO 4 production from the sCI reaction channel is the lack of experimentally determined reaction rates for sCIs formed from isoprene ozonolysis with SO 2 along with systematic discrepancies in experimentally derived reaction rates between other sCIs and SO 2 and water vapor. In general, the maximum of H 2 SO 4 production from the sCI channel is found in the late afternoon as ozone increases toward the late afternoon. The sCI channel, however, contributes minor H 2 SO 4 production compared with the conventional OH channel in the mid-day. Finally, the production and the loss rates of H 2 SO 4 are compared. The application of the recommended mass accommodation coefficient causes significant overestimation of H 2 SO 4 loss rates compared with H 2 SO 4 production rates. However, the application of a lower experimental value for the mass accommodation coefficient provides good agreement between the loss and production rates of H 2 SO 4 . The results suggest that the recommended coefficient for the H 2 O surface may not be suitable for this relatively dry environment. ■ INTRODUCTIONMost sulfur compounds emitted to the atmosphere are in a reduced form (e.g., sulfur dioxide, SO 2 (IV)). Atmospheric gasphase oxidation processes sulfur throughout the troposphere and the stratosphere and transforms these emitted sulfur compounds into the most oxidized form of gas-phase sulfuric acid (H 2 SO 4 ), unless heterogeneous uptake transforms the sulfur into condensed-phase forms. The discussion in this paper will focus exclusively on gas-phase H 2 SO 4 formation from gas-phase SO 2 oxidation. Although sulfur compounds contribute a relatively minor fraction of the chemical composition of the troposphere, 1 the critical role of H 2 SO 4 in determining acidity in precipitation 2 and forming particles that influence regional and global climate has been highlighted. 3−5 Anthropogenic sulfur emission in the form of SO 2 is currently estimated to dominate global sulfur emissions, followed by oceanic dimethylsulfide (CH 3 SCH 3 ). 6 The gas-phase atmospheric oxidation processes of SO 2 were thought previously to be driven mostly by hydroxyl radical (OH), as shown in R1−R3. 7The potential role of stabilized Criegee biradicals (sCIs) 8 in SO 2 oxidation has been discussed since the 1970s. Cox and Penkett 9 reported significant SO 3 formation rates from chamber experiments with various alkene compounds, ozone (O 3 ), and SO 2 . They speculated sCIs prompted SO 2 oxidation because the reaction between SO 2 and O 3 is insignificant under atmospheric conditions. Calvert and Stockwell 2 presented comprehensive zero-dimensional model calculation results examining atmosp...