Source Profiles of Particle-Bound Phenolic Compounds and Aromatic Acids From Fresh and Aged Solid Fuel Combustion: Implication for the Aging Mechanism and Newly Proposed Source Tracers

Phenolic compounds and aromatic acids, as oxygenated aromatic compounds, can participate in photochemical reactions to form secondary organic aerosols (SOAs), and thus strongly impact climate and human health. In the present study, on-site combustion experiments were conducted to determine primary emissions and secondary formation of phenolic compounds and aromatic acids released from burning of a variety of solid fuels using a potential aerosol mass-oxidation flow reactor (PAM-OFR). Emission factors (EFs) of phenolic compounds and aromatic acids from aged samples were 1.04 to 4.04 and 0.90 to 2.80 times those in the fresh PM_2.5, respectively, implying significant amounts of these compounds produced from atmospheric aging processes. Substantially different emission profiles of phenolic compounds were observed between coal and biomass burning, with coal combustion mainly released single-ring species (82%–86% in primary and 86%–89% in secondary emissions), while biomass burning released more two-, three-, and four-ring species (59%–69% in primary and 50%–58% in secondary emissions). Aromatic acids emission profiles from coal and biomass burning also differed considerably, with biomass burning producing significantly higher (>2 times) abundance of dibasic acids than coal combustion, suggesting higher potential of producing additional -COOH group from biomass burning. Benzenediol, cresol, dimethylphenol, 1-pyrenol, phenanthrenol, and hydroxylbenzonic acid were identified as SOA as they were mainly formed during simulated aging processes. Benzenediol acid/phenanthrenol was much lower from biomass (3.70 ± 1.29) than coal (62.7 ± 9.61), and these values remained stable after aging, suggesting this ratio being suitable as tracer for distinguishing different fuels combustion in source apportionment analysis.