The incidence of severe wildfires in the southern Great Plains, USA, has steadily increased in the last 25 years. The Rhea Fire in 2018, for example, burned roughly 300 000 acres of tallgrass prairie in western Oklahoma. Biomass burning organic aerosol (BBOA) from these grassfires has significant but uncertain effects on climate, as there are many remaining questions regarding its interactions with solar radiation and cloud processes. Using experimental and computational techniques, we are working to contribute insights into the light-absorption and hygroscopicity of primary and secondary BBOA from regionally relevant fuel species. Light-absorption of primary BBOA is characterized in terms of the mass absorption coefficient (MAC) using UV-vis spectroscopy for a range of fuels, including tallgrasses collected in summer and winter as well as eastern red cedar. The potential role of charge-transfer complexes in the light absorption of this BBOA is probed by determining the effects of concentration and temperature on absorbance. The distribution of absorbance, mass, and in turn MAC values across a range of polarity fractions is determined using octanol-water partitioning. The hygroscopicity of the BBOA is measured using a tandem differential mobility analyzer. Furthermore, the evolution of light-absorption and hygroscopicity with laboratory-simulated atmospheric aging is monitored. Together, these results will help to better understand the fate and impact of BBOA from wildfires in the southern Great Plains.

Light-absorption, hygroscopicity, and aging of biomass burning organic aerosol in the southern Great Plains

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