Properties of Surface-Active Organics in Aerosol Particles Produced from Combustion of Biomass Fuels under Simulated Prescribed-Fire and Wildfire Conditions

Abstract

The interfacial properties of the organic fraction of biomass burning aerosols (BBA), such as the critical micelle concentration (CMC) and surfactant composition, may vary based on the origin and moisture content of the fuel and the resulting combustion conditions. Surfactant composition, fraction of total particle mass, surface tension minimums, and CMC values of organics extracted from fresh and aged BBA produced using fuel beds from Georgia ecoregions (Piedmont, Coastal Plain, and Blue Ridge) and with fuel moisture contents representative of prescribed fires or drought-induced wildfires were measured using high resolution mass spectrometry, UV–vis spectroscopy, and pendant drop tensiometry. Surface tension minimums of organics extracted from all BBA were low (<45 mN m^–1), and surfactants were ∼2% of the total particle mass. The surfactant fraction was tied to combustion conditions, with the highest fractions present in BBA produced from the most efficient (highest temperature) combustion. Aging of BBA using a potential aerosol mass oxidative flow reactor resulted in an increase in the surfactant fractions of total BBA mass. The dependence of the surfactant fraction on combustion conditions may have implications for the microphysics of BBA from wildfires and prescribed fires.

Understanding the chemical and physical characteristics of surfactants in biomass burning aerosols is important for understanding their influence on the climate. The concentration, composition, and surface tension of surface-active organics in biomass burning aerosol varied based on the fuel-bed composition and moisture content.