In 2025, the second iteration of a multidisciplinary campaign known as the Georgia WIldland-fire Simulation Experiment (G-WISE 2) was conducted. G-WISE 2 focused on how different wildfire fuel conditions, such as fuel bed moisture, mass loading, and the inclusion of a high organic fuel known as duff (Zhang et al, 2022), influenced the aerosols produced from the combustion of the fuel beds. 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) (Stephens et al., 2003). During G-WISE-2, an SP2 was deployed downstream of a thermodenuder to quantify BC concentration, coating thickness and volatility as a function of the fuel-bed condition. Coating thickness with the SP2 was measured via the conventional “leading-edge-only (LEO) fit” analysis method (Gao et al, 2007). The thermodenuder was operated at 100°C or 300°C to evaporate BC coatings of differing volatility. We show that the burning of the duff fuel layer led to heavily coated BC particles with semi-volatile coatings often persisting even after thermodenuding at 300°C whereas in burns without duff the resulting BC coating almost entirely evaporates at 300°C. Lastly, during the duff burns, we observed charring of the organic coatings with the thermodenuder as evident by an increase in both number of particles that incandesced and the intensity of incandescence.

References

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2. 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
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