Atmospheric aerosols affect the earth's energy budget directly by scattering the solar radiation and indirectly by acting as cloud condensation nuclei to form clouds. The magnitude of these effects strongly depends on their chemical composition, size distribution and spatial distribution. A deep convective cloud system is where the tropospheric aerosols change their distribution and composition drastically in a short time through the interactions among the chemical, microphysical and dynamical processes of the clouds. In this study, the formation and re-distribution of sulfate aerosols in a deep convective cloud system are investigated using a cloud/chemistry model. The model is a non-hydrostatic, quasi-compressible and three-dimensional cloud model with detailed microphysics and explicit sulfur chemistry. Six water substances included are water vapor, cloud water, rain water, ice crystals, snow crystals and graupel/hail. The interactions between sulfur species and the water substances considered are: 1) the activation of sulfate aerosols, 2) the absorption of sulfur dioxide by water drops, 3) the oxidation of dissolved sulfur species by hydrogen peroxide to produce sulfate, 4) the impaction scavenging of unactivated interstitial sulfate aerosols by hydrometeors, and 5) the production of new sulfate aerosols by evaporation and sublimation of hydrometeors. In order to formulate these processes, the number concentration and size distribution of sulfate aerosols and hydrometeors are taken into account. The 1981 August 2 CCOPE Supercell storm in Montana is taken as a model convective system for the study. Sulfate aerosols are prescribed in a vertical profile that is typical of industrialized areas of North America. The model results show the oxidation of sulfur dioxide by hydrogen peroxide contributes to the production of sulfate aerosols. The production of sulfate through this process is oxidant limited in this case. The high concentration of sulfate within hydrometeors is found in the updraft and outflow region of the clouds. A large portion of the sulfate is associated with snow and graupel/hail. This indicates the importance of riming processes in the re-distribution of sulfate during the evolution of the storm
Symposium on Interdisciplinary Issues in Atmospheric Chemistry