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

Abstract

Abstract. Semi-volatile organic compounds (SVOCs) emitted from open biomass-burning (BB) can contribute to chemical and physical properties of atmospheric aerosols and also may cause adverse health effects. The polar fraction of SVOCs constitutes a significant part of BB organic aerosols, and thus it is important to characterize the chemical composition and reactivity of this fraction. In this study, globally and regionally important representative fuels (Alaskan peat, Moscow peat, Pskov peat, Eucalyptus, Malaysian peat, and Malaysian agricultural peat) were burned under controlled conditions using the combustion chamber facility at the Desert Research Institute (DRI). Gas- and particulate-phase biomass-burning emissions were aged in an oxidation flow reactor (OFR) to mimic 5–7 days of atmospheric aging. Fresh and OFR-aged biomass-burning aerosols were collected on Teflon impregnated glass fiber filters (TIGF) in tandem with XAD resin media for organic compound (OC) speciation. The polar fraction extracted with dichloromethane and acetone was analyzed with gas chromatography mass spectrometry (GC-MS) for 84 polar organic compounds – including mono and dicarboxylic acids, methoxylated phenols, aromatic acids, anhydrosugars, resin acids, and sterols. For all these compounds, fuel-based emission factors (EFs) were calculated for fresh and OFR-aged samples. The carbon mass of the quantified polar compounds was found to constitute 5 % to 7 % of the total OC mass. High abundance of methoxyphenols (239 mg kg−1 for Pskov peat; 22.6 % of total GC-MS characterized mass) and resin acids (118 mg kg−1 for Pskov peat; 14.5 % of total GC-MS characterized mass) was found in peat burning emissions (smoldering combustion). Concentration of some organic compounds (e.g., tetracosanoic acid) with molecular weight (MW) above 350 g mol−1 decreased after the OFR aging, while abundances of low MW compounds (e.g., hexanoic acid) increased. This indicated a significant extent of fragmentation reactions in the OFR. Methoxyphenols decreased after OFR aging, while a significant increase (3.7 to 8.6 times) in abundance of dicarboxylic acids emission factors (EFs), especially maleic acid (10 to 60 times), was observed. EFs for fresh and ratios from fresh-to-aged BB samples reported in this study can be used to perform source apportionment and predict processes occurring during atmospheric transport.

Emissions from the Open Laboratory Combustion of Cheatgrass (Bromus Tectorum)

“…Overall, the total EFs for the gas-and particle-phase organic compounds were 25 and 18 times lower for cheatgrass than those for ponderosa pine needles, and they were 6 and 12 times higher in comparison with the eucalyptus's gas and particle-phase EFs. We were not able to compare the total EFs for each group with those of Iinuma et al's [56] because the total number of analyzed polar organic compounds in each group was different from that in the present study and in Sengupta's and Yatavelli's research [48,57].…”

“…Sampling and analysis of organic emissions collected on XAD (gas-phase organic compounds) resin (Sigma-Aldrich, St. Louis, MO, USA) and filter samplers (particle-phase organic compounds) are described in detail by Sengupta et al [48] and Samburova et al [36]. Briefly, combustion emissions were collected on 100-mm diameter Teflon-impregnated glass fiber (TIGF) filters (Fiber Film T60A20, Pall Life Sciences, Ann Arbor, MI, USA), followed by a XAD-4 cartridge at a flow rate of 0.11 m 3 /min.…”

“…Briefly, combustion emissions were collected on 100-mm diameter Teflon-impregnated glass fiber (TIGF) filters (Fiber Film T60A20, Pall Life Sciences, Ann Arbor, MI, USA), followed by a XAD-4 cartridge at a flow rate of 0.11 m 3 /min. Immediately after sampling, the samples were stored at -20 • C. Prior to extraction, collected filters and XAD cartridges were spiked with deuterated internal standards of polar organic compounds [48]. The samples were extracted with an accelerated solvent extractor (ASE) system (DIONEX, ASE-300, Salt Lake City, UT, USA) at the following conditions: temperature: 80 • C, solvents: dichloromethane (150 mL) followed by acetone (150 mL), extraction cell pressure: 10.3 MPa, extraction time: 15 min.…”

“…After the extraction, the samples were pre-concentrated to 1 mL using a rotary evaporator at 35 • C and a gentle vacuum. The extracts were derivatized with N,O-Bis(trimethylsilyl)trifluoroacetamide (BSTFA) agent, as described elsewhere [49], and analyzed with gas chromatography-mass spectrometry (GC-MS) method [48] using Varian CP-3800 GC equipped with a CP-8400 autosampler and interfaced to a Varian 4000 Ion Trap Mass Spectrometer (Varian, Inc. Walnut Creek, CA, USA). Injections were performed into a 30 m length, 5% phenylmethylsilicone fused silica capillary column (DB-5MS, Agilent Technologies, Palo Alto, CA, USA) with an integrated deactivated guard column (length: 10 m).…”

“…Gas-and particle-phase organic compounds analyzed in cheatgrass combustion samples were assigned to nine groups based on their chemical structures (Table S1): alkanoic acids (20), alkenoic acids (5), benzoic acids and substituted benzoic acids (9), alkanedioic acids (15), aromatic dicarboxylic acids (2), anhydrous sugars (2), methoxyphenols (10), methoxy acids (9), and resin acids (7). The EFs are shown in Table 4, together with the EFs reported in previous studies [48,56,57]. For the particle phase, the highest EF among the identified compounds was for anhydrous sugars (98.3 ± 24.6 µg/g), followed by those for alkanedioic acids (26.2 ± 6.6 µg/g) and alkanoic acids (8.1 ± 2.0 µg/g).…”