Numerical studies of acidification processes within and below clouds with a flow-through chemical reactor model

Abstract

A flow-through chemical reactor model has been exercised to assess the importance of various oxidation reactions and cloud processes on wet removal and redistribution of atmospheric pollutants and to investigate the effect of in-cloud acidification on precipitation chemistry at the surface. Preliminary results indicate that in-cloud acidification accounts for more than 60% of the wet deposited acids derived from acidification of initial SO 2, that 42–57% of water-soluble, non-reactive NH 3 and HNO 3 are removed by wet deposition. The pseudo-first-order conversion rate of SO 2 to SO 4 2− ranges from 3 to 25% h −1 depending on initial and boundary conditions. Sensitivity studies have been carried out to test the importance of time evolution of clouds on partitioning of pollutants in the atmosphere and to investigate the variability of precipitation chemistry due to changes in rate constants. The distributions of NH 3 and HNO 3 are found to be dependent largely on the cloud microphysical parameters, while the distributions of H 2O 2 and SO 2 depend largely on initial conditions of both species. Individual physical and chemical mechanisms can determine the overall rate of sulfate wet deposition at different stages of cloud evolution.