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Chemical Transformation of Biomass Burning Organic Aerosol Due to Photolytic Aging
HONGMIN YU, Christopher Lim, Christopher Cappa, Jesse Kroll, Rachel O'Brien, William & Mary
Abstract Number: 305
Working Group: Aerosol Chemistry
Abstract
Biomass burning organic aerosol (BBOA) is a major research focus because of its important role in atmospheric chemistry and radiative forcing. Due to its chemical complexity, there are gaps in our knowledge about the chemical aging processes of BBOA in the atmosphere. Since many photochemical aging experiments on BBOA are usually conducted for only a few hours, relatively little is known about the photo-aging pathways of the system over an extended timescale. Here we present the analyses of several BBOA filter samples derived from burning of various types of biomass fuels that were aged by photolysis over a timeframe of up to ~3.5 days. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Offline-Aerosol Mass Spectrometry (Offline-AMS), and Ultraviolet–Visible Spectroscopy (UV/Vis) were used to measure the chemical changes in the aqueous sample extracts and evaluate how those changes can relate to the specific fuel type. This study finds an overall increase in oxidation state and decrease in the nitro group (‑NO2) compounds in the samples with irradiation. The AMS signal of levoglucosan, a tracer organic species of BBOA, is also observed to decrease in the sample mixture possibly due to the photolytic formation of oxidants in the condensed phase. Several unique chemical characteristics were observed for some samples, which can possibly relate to their individual fuel type. Observed changes demonstrate the rates of photo-bleaching and oxidation that can occur in BBOA from different fuel types when photolyzed as dry particles over ~3.5 days.