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Chemical Transformations of Biomass Burning Organic Aerosol within Wildfire Plumes - From Near-source to the Regional Scale
RYAN FARLEY, Timothy Onasch, John Shilling, Shan Zhou, Sonya Collier, Lawrence Kleinman, Arthur J. Sedlacek, Qi Zhang, University of California, Davis
Abstract Number: 489
Working Group: Wildfire Aerosols
Abstract
The atmospheric processing of biomass burning organic aerosol (BBOA), and the resulting implications on tropospheric aerosol composition and physicochemical properties, is still uncertain. This study investigates the transformation of BBOA within wildfire plumes during the DOE sponsored Biomass Burning Observation Project (BBOP) in the U.S. Pacific Northwest. Measurements of submicron particulate matter (PM1) concentration and composition between <1 and ~10 hours of photochemical processing were performed using a high-resolution aerosol mass spectrometer (HR-AMS) aboard the DOE G-1 aircraft. A second HR-AMS at the Mt. Bachelor Observatory (MBO) ground site provided complementary measurements of BBOA having undergone > 6 hours of processing during the campaign. In addition, highly aged plumes with more than 10 days of transport were sampled at MBO in summer 2019. Here we present the analyses of these strategically combined airborne and mountaintop measurements to investigate the near-field (< 1 hr) and regional evolution of BBOA properties in wildfire emissions located in the western U.S. We examine the evolution of the chemical properties of BBOA as a function of photochemical age, estimated by the ratio of NOx/NOy or NOx/CO. The freshest plume had extremely high OA loadings of up to 2000 µg m-3 and an average O/C of less than 0.25. After 6-8 hours of atmospheric transport, the BB plumes sampled at MBO had an increased O/C of 0.70 ± 0.04. The increase of O/C in aged wildfire plumes was associated with a decrease in the organic fraction at m/z 60 (f60), a HR-MS tracer ion for primary BBOA. Additionally, we also explore the formation of secondary organic aerosol (SOA) within the wildfire plumes by comparing the enhancement of OA relative to CO. Finally, positive matrix factorization analysis will be used to disentangle the contribution of primary BBOA from SOA formed through atmospheric reactions of volatile organic compounds. These results can be used to better understand and model the evolution of aerosols and the formation of SOA within these systems.