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Persistent Influence of Biomass Burning Aerosols during Clean Air Conditions in the Western United States
RYAN FARLEY, Noah Bernays, Daniel Jaffe, Qi Zhang, University of California, Davis
Abstract Number: 419
Working Group: Remote and Regional Atmospheric Aerosol
Abstract
Biomass burning (BB) is an important source of primary and secondary air pollutants, and biomass burning aerosols can directly influence regional and global air quality and climate. The aging of these aerosols and impacts on the remote background is still poorly understood. In this study, we deployed a high-resolution time-of-flight soot particle aerosol mass spectrometer (SP-AMS) coupled with a thermodenuder at the Mt. Bachelor Observatory (MBO) in Oregon to characterize the chemical composition and properties of wildfire-influenced aerosols during the summer of 2019 (Aug. 1 – Sept. 8). MBO is a high altitude site (~2800m a.s.l.) which has previously been used to examine long-range transport and BB plumes. Relatively low submicron aerosol concentrations (PM1) were seen (2.2±1.9 µg/sm3) compared to previous years, with the mass dominated by organic species (82.1%). Through positive matrix factorization analysis, an oxidized BB organic aerosol (BBOA) was found to comprise 18% of OA mass on average, and above 50% during plume events. This BBOA factor shows a high O/C (0.65), low volatility and a strong correlation with C2H4O2+ (m/z = 60.021), an SP-AMS BB tracer ion. Five biomass burning plumes were analyzed with transport times estimated to vary from ~10 hours to >10 days. The more processed biomass burning plumes consist of a higher fraction of the CO2+ ion to the total organic signal (f44), and a lower fraction of the C2H4O2+ ion (f60). The more aged plumes show lower volatility, and an increase in the peak mass-based size distribution from 400nm to 700nm, suggesting more pronounced aqueous phase processing. This work suggests that BB emissions significantly affect aerosol extinction and atmospheric chemistry in remote locations, with the chemical and physical properties varying depending on atmospheric processing.