Optical Properties of Biomass Burning Particles in the G-WISE Campaign

ZACHARY MCQUEEN, Ryan Poland, Chase Glenn, Omar El Hajj, Kruthika Kumar, Anita Anosike, Robert Penland, Rawad Saleh, Joseph O'Brien, Geoffrey Smith, University of Georgia

     Abstract Number: 30
     Working Group: Carbonaceous Aerosol

Abstract
Studies of the radiative effects of biomass burning aerosols have largely been dedicated to those generated by wildfires. Prescribed fires, however, play a significant role in forest management and ecological development, and there is a lack of fundamental science supporting regulations governing prescribed burns (1). The Georgia Wildland-fire Simulation Experiment (G-WISE) was a month-long, collaborative campaign in Athens, Georgia, designed to characterize the difference between wild (dry conditions) and prescribed (moist conditions) fires from fuels from three representative eco-regions in Georgia: Piedmont, Coastal Plain and Blue Ridge. Optical properties of the particle emissions were measured using a four-wavelength (406 nm – 783 nm) photoacoustic spectrometer for absorption and two cavity ringdown spectrometers (445nm and 663 nm) for extinction (2). For both wild and prescribed conditions, the single scattering albedo (SSA) at 663 nm was found to correlate strongly with the absorption Ångström exponent (AAE) over a wide range of SSA (0.70-0.99) and AAE (1-4). Combustion of the Blue Ridge fuel, which contains an organic rich sublayer (duff), produced aerosols with a large fraction of absorption, at 406 nm, attributable to brown carbon (70-78%), with high AAE (3.5-4.0) and high SSA (0.97-0.99). The AAE and SSAs were also found to be highly correlated with the elemental carbon to total carbon ratio (R2=0.95) measured with an EC: OC analyzer. The strong correlations observed between these optical properties could allow radiative transfer models to account for variability in biomass burning conditions and fuel types with a simple parameterization.

[1] Hiers, J. K. et al. Prescribed fire science: the case for a refined research agenda. Fire Ecol 16, 11 (2020).
[2] Fischer, D. A. & Smith, G. D. A portable, four-wavelength, single-cell photoacoustic spectrometer for ambient aerosol absorption. Aerosol Sci Tech 52, 393–406 (2018).