AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Influence of Wildfires on Aerosol Chemistry in the Western US and Insights into Atmospheric Aging of Biomass Burning Organic Aerosol: Results from BBOP
SHAN ZHOU, Sonya Collier, Dan Jaffe, Nicole Briggs, Jon Hee, Arthur J. Sedlacek, Lawrence Kleinman, Qi Zhang, University of California, Davis
Abstract Number: 524 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Biomass burning (BB) is one of the most important, yet poorly characterized, contributors to atmospheric aerosols on a global scale. Wildfire, in particular, represents a highly variable and typically uncontrollable source of BB emissions that impact regional air quality and global climate. As part of the DOE Biomass Burning Observation Project (BBOP) in summer 2013, we characterized the chemical composition of non-refractory submicron aerosols (NR-PM1) heavily impacted by wildfire emissions in the Pacific Northwest region of the United States at the Mt. Bachelor Observatory (MBO, ~ 2763 m a.s.l.), using a High Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS). Clean periods without BB influence were characterized by low NR-PM$_1 mass and high mass fraction of ammonium sulfate. The average NR-PM&_1 mass concentration increased substantially for periods impacted by transported BB plumes, and organic aerosol (OA) accounted on average for 94.6% of the NR-PM&_1 mass. Positive Matrix Factorization (PMF) of the AMS data identified five distinct OA factors, including three types of BBOA: a fresh semi-volatile BBOA-1 (O/C = 0.33), an intermediately oxidized BBOA-2 (O/C = 0.62), and a highly oxidized, low-volatility BBOA-3 (O/C = 1.07). BBOA-2 and BBOA-3 together accounted for an average ~52% of the total OA mass. Additionally, analysis of persistent BB plume events transported from single fire sources indicates that longer photochemical processing led to higher BBOA oxidation degree and higher mass fractional contribution of the chemically aged BBOA-2 and BBOA-3. deltaOA/deltaCO enhancement ratios showed little change for BB plumes transported primarily at night versus daytime, although substantial chemical transformation in OA was observed for daytime plumes due to photo-oxidation. These results suggest insignificant net OA production arising from photo-oxidation in BB plumes and that SOA formation due to heterogeneous oxidation was almost entirely balanced by OA volatilization.