Regional Radiative Impacts of Dark Brown Carbon in the Southeast United States

ALEXANDRA NG, ManishKumar Shrivastava, Brian Gaudet, Cenlin He, Zezhen Cheng, William Vizuete, University of North Carolina at Chapel Hill

     Abstract Number: 223
     Working Group: Burning Questions of Aerosol Emissions, Chemistry, and Impacts from Wildland-Urban Interface (WUI) Fires

Abstract
Aerosols influence the Earth’s radiative budget, directly by absorption (warming) or scattering (cooling), and indirectly as cloud condensation nuclei. While most organic aerosols primarily scatter light, black carbon (BC) and brown carbon (BrC) contribute significantly to absorption. BC and BrC are emitted from fossil fuel burning and biomass burning. Recently, dark brown carbon (d-BrC), a subset of BrC, has been found to contribute a direct radiative effect of +0.208 W/m2 which is comparable to BC. However, dark brown carbon has not been incorporated into air quality models. In this work, we introduced primary dark brown carbon as a new species in WRF-Chem, assuming an emission rate to be 20% of organic carbon from biomass burning. We modeled dark brown carbon (d-BrC) in the Southeast United States from June 12th, 2013 to June 30th, 2013 with the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) version 4.2. We utilized novel experimentally-derived refractive indices for dark brown carbon. The model was evaluated with ground-based organic aerosol and gas measurements collected during the Southern Oxidant and Aerosol Study 2013 field campaign, as well as 9 flights with radiative forcing measurements. The implications of the model evaluation on the importance of dark brown carbon in radiative budgets will be discussed.