Seminar

Abstract

Organic aerosols (OA) play an important role in climate change. However, there are few estimates for the radiative forcing of OA that include secondary organic aerosol (SOA) or the light-absorbing part of OA (brown carbon). Here we use a global model with an explicit formation mechanism for SOA to assess the radiative forcing associated with the change in both primary organic aerosol (POA) and SOA between present-day and preindustrial conditions. Anthropogenic emissions are shown to almost double the SOA formation rate and increase its burden by almost 50% (0.4 Tg) while the POA burden increases slightly more (0.51 Tg). Gas phase partitioning explains 45% of the increase in SOA, aqueous phase reactions of glyoxal and methylglyoxal explain 25%, and the formation of epoxides from the oxidation of isoprene explains 30%. The direct radiative forcing of SOA ranges from -0.12 to -0.31 Wm^-2 and the first indirect forcing ranges from -0.22 to -0.29 Wm^-2. We also discuss the possible role of SOA formation in cirrus clouds.