Biomass Burning Black Carbon Properties during the G-WISE Campaign using the Single Particle Soot Photometer (SP2)

JOHN ALLEN, Ryan Poland, Zachary McQueen, Dongli Wang, Andrew Metcalf, Joseph O'Brien, Rawad Saleh, Geoffrey Smith, University of Georgia

     Abstract Number: 448
     Working Group: Remote and Regional Atmospheric Aerosol

Abstract
The Single Particle Soot Photometer (SP2) is used to measure black carbon (BC) concentrations and the mixing state of individual particles using laser-induced incandescence and scattering signals (Stephens et al. 2003). The SP2 was employed at the Georgia WIldland-fire Simulation Experiment (G-WISE), a multidisciplinary campaign in which fuel beds from three different eco-regions of Georgia (Piedmont, Coastal Plain, and Blue Ridge) were burned to simulate wild (lower fuel moisture content) and prescribed (higher fuel moisture content) fires. Here, we use measurements of the “delay time” between the peak of BC incandescence and the peak of scattering to infer the relative coating thickness (Moteki and Kondo, 2007) for the different fuel beds and moisture contents and use a thermodenuder in tandem with the SP2 to infer coating volatility. We then use these techniques to also study the effect of oxidative aging on the BC coatings by exposing BC to oxidants through an oxidative flow reactor. Aging increases the delay time for particles from all fuel beds indicating thicker coatings. A comparison of delay times with and without the thermodenuder demonstrates that a substantial fraction of the coatings evaporates from Blue Ridge particles, whereas very little appears to evaporate from Coastal Plain particles, indicating a difference in coating volatility for particles generated from these two types of fuel beds. The Blue Ridge fuel contains duff, decaying organic material with high moisture content (Zhang et al. 2022), while Coastal Plain does not. The additional burning of duff provided particles generated Blue Ridge with different organic material to form coating contributing to the observed higher volatility.

References
[1] Stephens, M., Turner, N. & Sandberg, J. (2003) Particle identification by laser-induced incandescence in a solid-state laser cavity. Appl. Opt. 42, 3726. doi:10.1364/AO/42.003726.
[2] Moteki, N. & Kondo, Y. Effects of Mixing State on Black Carbon Measurements by Laser-Induced Incandescence. Aerosol Sci Tech 41, 398–417 (2007). doi:10.1080/02786820701199728.
[3] Zhang, A., Liu, Y., Goodrick, S. & Williams, M. D. Duff burning from wildfires in a moist region: different impacts on PM2.5 and ozone. Atmos Chem Phys 22, 597–624 (2022). Doi: 10.5194/acp-22-597-2022.