Estimating the Mass Extinction Cross Section of Carbonaceous Aerosols from African Biomass Burning


Atmospheric Science Undergraduate Program, North Carolina A&T State University

Document Type


Publication Date

Spring 2023


Biomass-burning (BB) is the process of burning organic matter such as forests, grasslands, and agricultural waste for land clearance, agriculture, and waste disposal. BB is a major source of atmospheric aerosols, i.e., tiny particles suspended in the air. BB aerosols impact climate by scattering and absorbing sunlight, which can affect the Earth's energy balance. The aerosol mass extinction cross-section (MEC) is a measure of the effectiveness of these aerosols in reducing the amount of light that reaches the Earth's surface. It is expressed in units of area per aerosol mass. We conducted a study using the NC A&T indoor smog chamber and burn facility to understand the impact of biomass burning aerosols emitted from burning African biomass fuels. Eleven different biomass fuels including hardwoods, savanna grass, and cow-dung, were combusted under controlled conditions. The resulting organic-rich emissions were exposed to humid (relative humidity, RH, above 40%) and dry (RH <10%) conditions. The study estimated the MEC of the emissions under three different aging states: primary (directly emitted to the chamber), dark-aged (physical ageing of primary emissions in the dark), and photo-aged (dark-aged particles exposed to UV-radiation). MEC calculation is based on extinction coefficients determined by a cavity ring down spectrometer and aerosol mass concentrations by a scanning mobility particle sizer. Preliminary findings suggest that emissions exposed to intermediate relative humidity typically exhibit a lower MEC at 550 nm than their dry counterparts. This data is important to understand the impact of biomass burning aerosols on air quality and regional climate in Africa.

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