Coating Thickness and Coating Volatility of Black Carbon Particles from Simulated Wildland Fires Depends on Combustion Conditions

JOHN ALLEN, Ryan Poland, Muhammad Abdurrahman, Mike Lesiak, Mac A. Callaham, Michael Caraway, Thomas Carroll, Dongli Wang, Joseph O'Brien, Rawad Saleh, Andrew Metcalf, Pengfei Liu, Geoffrey Smith, University of Georgia

     Abstract Number: 384
     Working Group: Combustion

Abstract
The Georgia WIldland-fire Simulation Experiment (G-WISE) was a multidisciplinary campaign that studied combustion emissions from fuels collected in various eco-regions of Georgia at either high or low moisture levels. From G-WISE, McQueen et al. (2024) concluded that the impact of net cooling or warming from the aerosols of wildfire smoke is dependent on fuel-bed composition and moisture content. Black carbon (BC) is a primary absorber emitted in wildfire smoke which can be measured at the single particle level using incandescence signals in the Single Particle Soot Photometer (SP2). In 2025, the second iteration of G-WISE (G-WISE-2) expanded the investigation of wildfire fuel conditions by testing more fuel-bed conditions such as specific moisture, mass loading, and further exploring the impacts of a high organic surface fuel known as duff (Zhang et al, 2022). During G-WISE-2, two SP2’s were deployed in parallel and downstream of a thermodenuder to quantify BC concentration, coating thickness and volatility as a function of the fuel-bed condition. Coating thickness with SP2 was measured via the conventional “leading-edge-only (LEO) fit” coating analysis and through the particle’s “delay time” which is the time between the peak of incandescence (BC) and the peak scattering signal (coating). The thermodenuder was used at 100°C or 300°C to evaporate BC coatings of differing volatility. Using the delay time method for BC coating quantification, we show that the burning of the duff fuel layer led to heavily coated BC particles with ultra-low coatings, often persisting even after thermodenuding at 300°C. At higher moisture levels of the duff layer, its resistance to high temperature combustion resulted in the smoke being dominated by the combustion of fine surface fuel and we observed reduced BC coating thickness and volatility as indicated by relatively small changes in delay time between non-thermodenuded and at 300°C thermodenuded BC populations.