Investigating global brown carbon from both measurements and models

Abstract:

Brown carbon (BrC) is the component of organic aerosols (OA) which strongly absorbs solar radiation in the near-UV range of the spectrum. BrC properties and the resulting radiative effects are highly uncertain, limiting our ability to estimate near-term and regional climate forcing. Since both the source and optical properties of BrC are not well understood, it is challenging to develop a reliable model frameworks for BrC. On the other hand, field and laboratory measurements of BrC are rare and provide limited constraints.

BrC absorption exhibits strong spectral dependence, which differs from black carbon (BC), the other important fine aerosol absorber. Based on this property, we develop an innovative approach to derive BrC absorption from multi-wavelength absorption measurements. By analyzing the Aerosol Absorption Optical Depth (AAOD) data from global AERONET network, we find that the optical properties of BrC are connected to the BC/OA ratio, as suggested by recent work. In view of this finding, we develop and discuss a series of different methods to simulate BrC absorption in the GEOS-Chem global model and estimate an associated range for global BrC burden and direct radiative forcing (DRF).