Sulfur chemistry in smelter and power plant plumes in the western U.S.

Abstract

This paper summarizes the results from studies of SO 2(g) to particle conversion in the plume of a copper smelter and two coal fired power plants located in the Great Basin desert region and an oil fired power plant located on the California coast. Daytime formation of H 2SO 4 from SO 2(g) is dominated by a reaction which is first order in SO 2(g) and is temperature dependent, the rate of reaction increasing with increasing temperature. Neutralization of the H 2SO 4 is limited only by the rate of introduction of basic material from ambient air. NH 3 is not the principal base present except on the California coast. Metal oxides and carbonates (e.g., CaCO 3) are the predominant bases present in the inland desert areas. Two different classes of aerosol S(IV) compounds are formed from the interaction of SO 2(g) with participate matter, organic S(IV) species which can hydrolyze to give sulfite and inorganic S(IV) complexes. The inorganic species predominate in smelter plumes while formation of both the inorganic and the organic S(IV) compounds occurs in plumes from combustion of fossil fuels. Formation of the inorganic S(IV) complex is equilibrium controlled and is favored by high SO 2(g) and soluble aerosol Fe and Cu concentrations and by low aerosol acidity. Formation of the organic S(IV) compound follows first order in SO 2(g) reaction kinetics with the rate being inversely proportional to absolute humidity. The relative amounts of sulfate and the two classes of S(IV) compounds are dependent on the ambient temperature and humidity. Formation of the organic S(IV) compound predominates under cold dry conditions while formation of sulfate predominates when the air mass is warm and moist.