Aerosol growth and chemical change : models for arid environments

Abstract

Atmospheric aerosols, exposed to various dispersing gases, undergo evolution of chemical composition and subsequent growth/ shrinkage. The model developed considers a multi-component aerosol particle situated within a smelter plume. The particle evolves with respect to size and composition due to the absorption of gases, both emitted and ambient. Processes to be considered in this absorption are: diffusion of gases to the particle surface, gas/liquid interfacial equilibrium, and liquid phase chemistry. The gases in the plume undergo advection, turbulent diffusion, settling, and gas-to-particle conversion, dispersing eventually into a low humidity environment. The conversion mechanism was first considered a simple first-order removal term, then considered to be a function of liquid phase chemistry. The model is applied to consider secondary sulfate formation within a copper smelter plume in an arid environment. Sulfate formation is found to occur early in the plume trajectory, where SO2 levels are highest, and is a strong function of ambient ammonia levels. Also, particles emitted into arid conditions are found to shrink to smaller, highly acidic particles in equilibrium with the dry, ambient conditions. Predictions are made of downwind gas phase pollutant levels as well as final chemical composition and particle size of the emitted aerosols.