VOLCANIC SULFUR EMISSIONS - ESTIMATES OF SOURCE STRENGTH AND ITS CONTRIBUTION TO THE GLOBAL SULFATE DISTRIBUTION

Anthropogenic emission of SO2 and conversion into SO42- is argued to b e the most important factor damping and modulating the global greenhou se effect. Recent estimates of the relative strength of the three impo rtant sources of volatile sulfur (SO2 from fossil fuel combustion simi lar to 78 Tg S/yr, from biomass burning similar to 2 Tg S/yr, and from natural sources similar to 25 Tg S/yr) suggest an over-whelming effec t of the anthropogenic emissions for climate forcing. However, the rad iatively relevant product SO42- may have different patterns due to the distribution of the sources (some very dense areas near the surface f or anthropogenic SO2, formation of SO2 from dimethylsulfide in the mar ine boundary layer, and emission of volcanic SO2 mostly in the free at mosphere in rural areas). In this paper we study the relative contribu tion of volcanic SO2 emissions to the atmospheric sulfur budget applyi ng an atmospheric general circulation model including a full sulfur cy cle and prescribed source distributions. An off-line analysis tool is applied to determine the radiative forcing of sulfate aerosols. The re sults show that natural S sources are at least as important as the ant hropogenic ones, even though their source strength is much smaller. Th e reasons are different lifetimes due to different production and emis sion processes. Therefore, we should improve our knowledge about the v olcanic volatile sources and their rime-space variability.