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PhD Defense

Department of Atmospheric Science

Mon.. July 24, 3:10 pm, EN6085

Quantification of absorption due to black and brown carbon from biomass burning and parameterization for comparison to climate models results

Rudra Pokhrel

University of Wyoming


Open Biomass Burning is one of the largest sources of black and brown carbon emissions on a global scale. But the atmospheric loading of black and brown carbon aerosol and their optical properties are highly uncertain. There is especially large uncertainty regarding the significance of brown carbon absorption. This presentation discusses the result from the fourth Fire Lab at Missoula Experiment (FLAME-4) which took place in October and November 2012. The results from the controlled laboratory burning of a wide range of biomass chosen based on their significance in global wildfires and cooking emissions are presented. Single scattering albedo (SSA), absorption Angstrom exponent (AAE), and absorption enhancement () from the fresh emissions show good correlation with the elemental carbon (EC) to organic carbon (OC) ratio and show less dependency on fuel types and modified combustion efficiency (MCE). A regression model is proposed to parameterize SSA and AAE based on EC/OC and the model accurately predicts the SSA during the first few hours of plume aging in the plume of a wildfire in Mexico. Regression models proposed in this study will help assess how reasonable SSA generated from models is. This study found that brown carbon can significantly reduce the SSA at short-visible wavelengths and have absorption equally or more important than absorption due to black carbon in this region. In addition, brown carbon can contribute up to 92 % of the total absorption at 405 nm and the fraction of absorption due to brown carbon shows reasonably good correlation with the EC/OC and AAE. Furthermore, photo-chemical processing of brown carbon absorptive properties is explored.

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