Polar semi-volatile organic compounds in biomass burning emissions and their 2 chemical transformations during aging in an oxidation flow reactor 3

Abstract

10 Semi-volatile organic compounds (SVOCs) emitted from open biomass-burning (BB) can 11 contribute to chemical and physical properties of atmospheric aerosols and also may cause adverse 12 health effects. The polar fraction of SVOCs constitutes a significant part of BB organic aerosols, 13 and thus it is important to characterize the chemical composition and reactivity of this fraction. In 14 this study, globally and regionally important representative fuels (Alaskan peat, Moscow peat, 15 Pskov peat, Eucalyptus, Malaysian peat, and Malaysian agricultural peat) were burned under 16 controlled conditions using the combustion chamber facility at the Desert Research Institute (DRI). 17 Gasand particulate-phase biomass-burning emissions were aged in an oxidation flow reactor 18 (OFR) to mimic 5–7 days of atmospheric aging. Fresh and OFR-aged biomass-burning aerosols 19 were collected on Teflon impregnated glass fiber filters (TIGF) in tandem with XAD resin media 20 for organic compound (OC) speciation. The polar fraction extracted with dichloromethane and 21 acetone was analyzed with gas chromatography mass spectrometry (GC-MS) for 84 polar organic 22 compounds—including mono and dicarboxylic acids, methoxylated phenols, aromatic acids, 23 anhydrosugars, resin acids, and sterols. For all these compounds, fuel-based emission factors (EFs) 24 were calculated for fresh and OFR-aged samples. The carbon mass of the quantified polar 25 compounds was found to constitute 5% to 7% of the total OC mass. High abundance of 26 methoxyphenols (239 mg kg-1 for Pskov peat; 22.6% of total GC-MS characterized mass) and resin 27 acids (118 mg kg-1 for Pskov peat; 14.5 % of total GC-MS characterized mass) was found in peat 28 burning emissions (smoldering combustion). Concentration of some organic compounds (e.g., 29 tetracosanoic acid) with molecular weight (MW) above 350 g mol-1 decreased after the OFR aging, 30 while abundances of low MW compounds (e.g., hexanoic acid) increased. This indicated a 31 significant extent of fragmentation reactions in the OFR. Methoxyphenols decreased after OFR 32 https://doi.org/10.5194/acp-2019-1179 Preprint. Discussion started: 23 January 2020 c © Author(s) 2020. CC BY 4.0 License.