Trace gas and aerosol interactions in the fully coupled model of aerosol-chemistry-climate ECHAM5-HAMMOZ: 2. Impact of heterogeneous chemistry on the global aerosol distributions

Abstract

We use the ECHAM5-HAMMOZ aerosol-chemistry-climate model to quantify the influence of trace gas-aerosol interactions on the regional and global distributions and optical properties of aerosols for present-day conditions. The model includes fully interactive simulations of gas phase and aerosol chemistry including a comprehensive set of heterogeneous reactions. We find that as a whole, the heterogeneous reactions have only a small effect on the SO 2 and sulfate burden because of competing effects. The uptake of SO 2 on dust and sea salt decreases the SO 2 concentrations while the decrease in OH (that results from the uptake of HO 2, N 2 O 5, and O 3) tends to increase SO 2 (because of reduced oxidation). The sulfate formed in sea salt aerosols from SO 2 uptake accounts for 3.7 Tg(S) a -1 (5%) of the total sulfate production. Uptake and subsequent reaction of SO 2 on mineral dust contributes to a small formation of sulfate (0.55 Tg(S) a -1, <1%), but is responsible for the coating of mineral dust particles, resulting in an extra 300 Tg a -1 of dust being transferred from the insoluble to the soluble mixed modes. The burden of dust in the insoluble modes is reduced by 44%, while the total burden is reduced by 5% as a result of enhanced wet deposition efficiency. Changes in the sulfur cycle affect the H 2 SO 4 concentrations and the condensation of H 2 SO 4 on black carbon. Accounting for heterogeneous reactions enhances the global mean burden of hydrophobic black carbon particles by 4%. The changes in aerosol mixing state result only in a small change in the global and annual aerosol optical depth (AOD) and absorption optical depth (ABS), but have significant implications on regional and seasonal scale. For example, in the main polluted regions of the Northern Hemisphere, AOD and ABS increase by 10-30% and up to 15%, respectively, in winter. Copyright 2008 by the American Geophysical Union.