Sulfate Production and Deposition in Midlatitude Continental Cumulus Clouds. Part II: Chemistry Model Formulation and Sensitivity Analysis

Abstract

We examine characteristics of in-cloud sulfate chemistry using a 1.5-dimensional Eulerian cumulus cloud model. Specifically we present here a study of (i) the relative importance of aerosol scavenging to in-cloud production of sulfate through oxidation of sulfur dioxide by ozone and hydrogen peroxide, (ii) the importance of the entrainment of environmental air in the formation and subsequent deposition of sulfate, (iii) the role of ice phase microphysical processes in determining the chemical properties of precipitation, and (iv) the chemical effects on clouds due to a modification of the environment by previous clouds. The results for a continental background or moderately polluted atmosphere indicate that aerosol scavenging accounts for between 50% and 80% of the in-cloud sulfate ultimately deposited; that ozone oxidation of sulfur dioxide may be important in the upper regions of the cloud; that although entrainment of environmental air is important in the cloud dynamics and microphysics, it is relatively unimportant in the chemistry; and that neglect of the ice phase when considering chemistry in them clouds may lead to overestimates of about 200% in sulfate deposition.