A contribution of brown carbon aerosol to the aerosol light absorption and its radiative forcing in East Asia

Brown carbon aerosols were recently found to be ubiquitous and effectively absorb solar radiation. We use a 3-D global chemical transport model (GEOS-Chem) together with aircraft and ground based observations from the TRACE-P and the ACE-Asia campaigns to examine the contribution of brown carbon aerosol to the aerosol light absorption and its climatic implication over East Asia in spring 2001. We estimated brown carbon aerosol concentrations in the model using the mass ratio of brown carbon to black carbon (BC) aerosols based on measurements in China and Europe. The comparison of simulated versus observed aerosol light absorption showed that the model accounting for brown carbon aerosol resulted in a better agreement with the observations in East Asian-Pacific outflow. We then used the model results to compute the radiative forcing of brown carbon, which amounts up to −2.4 W m−2 and 0.24 W m−2 at the surface and at the top of the atmosphere (TOA), respectively, over East Asia. Mean radiative forcing of brown carbon aerosol is −0.43 W m−2 and 0.05 W m−2 at the surface and at the TOA, accounting for about 15% of total radiative forcing (−2.2 W m−2 and 0.33 W m−2) by absorbing aerosols (BC + brown carbon aerosol), having a significant climatic implication in East Asia.