Incorporation of Brown Carbon into the CESM1 CAM5.4 and Model Comparison to Laboratory Optical Measurements

Improvements in the understanding of light absorbing organic carbon (BrC) allow for more accurate implementation of organic carbon optical properties in global climate models. Currently in the Community Earth System Model version 1 (CESM1) Community Atmosphere Model version 5 (CAM5) organic carbon (OC) is considered to be a purely scattering species. However, recent studies have shown that components of organic carbon released from combustion have a preferential absorption in the short wave that may help to account for discrepancies between observational and modeled global radiative forcing. Here, a parameterization for the radiative properties of organic carbon released from biomass burning, which takes into account organic carbon light absorption, is implemented in the CESM1 CAM5.4 (with the 4 mode Modal Aerosol Module (MAM4)). Black carbon and particulate organic matter Aerosol optical depth (AOD) and single-scattering albedo (SSA) from before and after the parameterization will be compared. The difference in radiative forcing will also be addressed to identify the effect of the optical modification. Observational comparisons of SSA and AOD come from AERONET sites in high biomass burning regions. The results of the model runs (with and without BrC) are also compared to a SSA vs Elemental Carbon(EC)/(EC+OC) parameterization developed in a laboratory burn chamber. This both verifies the accuracy of the model (in its similar distribution to the lab data) as well as gives another metric in determining the improvement of the model through incorporation of the radiative property parameterization.