Constraining solar absorption of organic aerosols from biomass burning and biofuel emissions with observations

 

Authors

Xiaohong Liu — Texas A&M University
V. Rao Kotamarthi — Argonne National Laboratory
David George Streets — Argonne National Laboratory
Yan Feng — Argonne National Laboratory
Zifeng Lu — Argonne National Laboratory

Category

Absorbing Aerosol

Description

Recent studies of spectrally resolved absorption measurements from the ARM and NASA/AERONET data sets suggest a significant amount of the globally observed absorption of solar radiation by aerosols is due to the absorbing organic aerosols (OA), referred to as “brown” carbon (BrC), especially over regions dominated by biomass burning and biofuel emissions. The solar absorption of OA in the latest CAM model has not been extensively examined with the spectral observations, which may affect the estimate of aerosol radiative forcing. Here we implement an optical treatment for the BrC absorption into the CAM model, and compare the calculated aerosol spectral absorption with ground-based AERONET and ARM observations. In this version of CAM5, biomass burning and biofuel OA are treated separately from fossil fuel OA with different imaginary refractive index. Because the absorption of BrC is highly variable and uncertain varying by source, aging, and mixing state, sensitivity studies of BrC refractive index parameterized by fuel type and ratio of BC to OA mass will be examined and the resulting uncertainty in the estimated forcing will be discussed. Our study intends to address the needs from the large-scale modeling perspective and challenges in modeling.