Evolution of Organic Aerosol From Wood Smoke Influenced by Burning Phase and Solar Radiation

Abstract

AbstractEmissions of carbonaceous aerosols (black carbon [BC] and organic aerosol [OA]) from biomass burning have important climate and human health impacts. Not only the primary emissions are complicated by combustion phases, but also the evolution after emission is not well understood. In this study, single plumes from residential wood burning, extracted from either flaming or smoldering phase, were injected into our novel chamber, to investigate their evolution in real atmospheric conditions with or without solar radiation. Initial compositions of flaming or smoldering plumes were dominated by BC or OA respectively, with higher NOx emission in flaming. Replicable results showed that in light, smoldering plumes had faster secondary OA (SOA) formation than flaming, due to the higher emissions of volatile organic compounds in smoldering. Furanic and carboxylic acid compounds were found to be the main gaseous precursors and products, respectively. Evaporation and photooxidation concurrently caused increased oxidation in the beginning, but at a later stage of evolution, SOA evolution showed remarkable divergence: enhanced oxidation for smoldering but decreased for flaming plumes, leading to a higher oxygen‐to‐carbon ratio for smoldering than flaming up to 0.25. We found the higher NOx emission in flaming promoted the gaseous fragmentation reactions, while the seeding particles dominated by OA in smoldering may cause these contrasting tendencies of OA oxidation between combustion phases. Distinct particulate/gas emissions and resultant evolutions in producing SOA at different combustion phases should be therefore considered in evaluating the impacts of biomass burning emissions.