American Association for Aerosol Research - Abstract Submission

AAAR 36th Annual Conference
October 16 - October 20, 2017
Raleigh Convention Center
Raleigh, North Carolina, USA

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Brown Carbon Chromophores from Biomass Burning and their Evolution during Oxidative Aging

BENJAMIN SUMLIN, Claire Fortenberry, Audrey Dang, Michael Walker, James Meyer, Brent Williams, Rajan Chakrabarty, Washington University in St. Louis

     Abstract Number: 614
     Working Group: Carbonaceous Aerosols in the Atmosphere

Abstract
Brown carbon (BrC), a class of organic aerosols (OA) with wavelength-dependent absorption, has received increasing attention as a key driver of global radiative forcing and climate change. Long-lasting smoldering wildfires emit large quantities of BrC in biomass burning OA (BBOA), and these emissions are responsible for a significant fraction of the total radiative forcing attributed to carbonaceous aerosols. However, the mechanisms by which these aerosols absorb light are not fully understood. Models that successfully describe the absorption behavior of black carbon aerosols, such as the bandgap theory, break down when applied to amorphous, non-crystalline structures.

We present results from simultaneous optical, physical, and chemical measurements of BBOA experiments performed in a large-scale laboratory emissions and combustion chamber. Integrated photoacoustic-nephelometer-spectrometers at three discrete wavelengths (375, 405, and 532 nm) measured absorption and scattering, while a suite of on- and off-line chemical and physical analyses were performed, including thermal desorption aerosol gas chromatography, high performance liquid chromatography, UV-VIS-IR spectrometry, x-ray photoelectron spectrometry, and particle size distribution measurement. The elemental and chemical composition of BBOA from several relevant global wildfire fuels was compared to chemical components found in solvent extractions of the fresh, un-combusted fuel to evaluate the influence of the combustion process (e.g., fire phase, moisture content, combustion efficiency) on chromophore formation. Key chromophore compounds are identified and their contributions to light scattering and absorption are tracked as a function of atmospheric aging, simulated by accelerating oxidative photochemistry in a potential aerosol mass (PAM) reactor.