Smick—A scavenging model incorporating chemical kinetics

Abstract

A scavenging model has been developed as an advanced tool for assessing the wet deposition of reactive gases and aerosols from point-source plumes. The model describes both the microscopic and macroscopic aspects of the plume-rain interaction, and predicts the concentrations of pollutant in rain at ground-level points below the plume. Microscopic interactions treated by the model include simultaneous mass transfer and chemical reaction, both outside and within the falling raindrops. Reversibility is incorporated within the mass-transfer description, thus allowing a realistic treatment of gas scavenging. Application of the model to the washout of SO 2 from power plant plumes, both with and without the assumption of chemical reaction within droplets, is described. These results indicate that sulfate levels found in rainwater below power-plant plumes are not adequately explained by traditional aqueous-phase conversion mechanisms involving oxidation of SO 2 by oxygen, at least when such conversion is limited to the below-cloud region. The model has been documented in user's-manual form, and is suggested for use in the general assessment of deposition impacts of pollution sources, such as fossil power plants.