Global distribution and climate forcing of carbonaceous aerosols

The global distribution of carbonaceous aerosols is simulated online in the Goddard Institute for Space Studies General Circulation Model II‐prime (GISS GCM II‐prime). Prognostic tracers include black carbon (BC), primary organic aerosol (POA), five groups of biogenic volatile organic compounds (BVOCs), and 14 semivolatile products of BVOC oxidation by O 3 , OH, and NO 3 , which condense to form secondary organic aerosols (SOA) based on an equilibrium partitioning model and experimental observations. Estimated global burdens of BC, organic carbon (OC), and SOA are 0.22, 1.2, and 0.19 Tg with lifetimes of 6.4, 5.3, and 6.2 days, respectively. The predicted global production of SOA is 11.2 Tg yr −1 , with 91% due to O 3 and OH oxidation. Globally averaged, top of the atmosphere (TOA) radiative forcing by anthropogenic BC is predicted as +0.51 to +0.8 W m −2 , the former being for BC in an external mixture and the latter for BC in an internal mixture of sulfate, OC, and BC. Globally averaged, anthropogenic BC, OC, and sulfate are predicted to exert a TOA radiative forcing of −0.39 to −0.78 W m −2 , depending on the exact assumptions of aerosol mixing and water uptake by OC. Forcing estimates are compared with those published previously.