Understanding Composition, Formation, and Aging of Organic Aerosols in Wildfire Emissions via Combined Mountain Top and Airborne Measurements

Wildfires are an important source of global aerosols that have pronounced impacts on regional air quality and global climate. A major component of wildfire emissions is organic, including primary organic aerosols (POA) and large amounts of gases that can be oxidized to form secondary organic aerosols (SOA). The environmental impacts of wildfire emissions are strongly correlated with the chemical, optical, and microphysical properties of biomass-burning organic aerosols (BBOA), which are dependent, in a complex manner, on combustion and atmospheric aging processes. Here we discuss results from recent field and laboratory studies aimed at understanding the chemical composition, formation, and evolution of BBOA in wildfire emissions. Comprehensive analysis of a large number of fresh and aged (up to days of aging) fire plumes originating in the Pacific Northwest region of the United States reveals that the enhancement of BBOA mass concentrations relative to the enhancement of the sum of CO and CO2 in wildfire smokes is primarily driven by combustion efficiency, whereas the composition and properties of the BBOA are strongly influenced by atmospheric oxidation and other aging processes. These results shed light on organic aerosol formation and transformation in biomass burning emissions.