Estimation of the Annual Contribution of US Sulfur Emissions to Canadian Acidic Deposition and Vice Versa

Abstract

The determination of a source-receptor relationship for acidic deposition has been one of the major thrusts of the National Acid Precipitation Assessment Program (NAPAP). The specific source-receptor relationship considered here is that showing the relative contribution of U.S. and Canadian sulfur emissions to deposition amounts. The results presented here are from a comprehensive Eulerian mathematical modeling system consisting of a core model, the Regional Acid Deposition Model (RADM) (Chang et al., 1987; Chang et al., 1990), a meteorological processor, MM4, (Seaman, 1989) and several interpretative tools. RADM consists of components which represent various atmospheric processes including: gas-phase photochemical production of ozone, hydrogen peroxide, and other oxidants from emissions of reactive organic compounds and oxides of nitrogen; oxidation of sulfur dioxide in both clear air and within cloud water; three-dimensional transport, mixing by clouds, and wet and dry deposition. The meteorological processor, MM4, which provides the information required as input for RADM is a mesoscale numerical weather prediction model using four-dimensional data assimilation (Seaman et al., 1990). The RADM is used episodically, that is, emissions and meteorological information for a specific weather event of three days duration are used for simulating the air concentration of important photochemical oxidants and other chemical species as well as the accumulated material which is deposited to the surface. The output files are then archived for future analysis using the interpretative tools. For the present discussion, the tool of choice is the Tagged Sulfur Engineering Model (TSEM).