The relative roles of emissions changes and meteorological variability in variation of wet sulfur deposition. A trajectory model study

Abstract

Wet deposition of sulfur oxides in eastern North America has been computed on a monthly time scale for 3 years, 1978–1980, using a Lagrangian trajectory model of long-range atmospheric transport in which wind flow and precipitation were determined from routine meteorological surface observations. Comparison between total monthly wet deposition of sulfur measured at 11 sampling locations from three monitoring networks in Ontario and neighboring states and the estimated wet deposition showed that the observed seasonal variation is simulated well by the model. Based on a sample of 177 paired monthly data points an r 2 = 0.5 was obtained and linear regression yielded a slope of 0.99 and intercept of 6.1 mg SO 4 2− m −2 month −1. This demonstrates the strong meteorological influence on the monthly variability of wet deposition, since model emissions were annual values. In a controlled model experiment the effects of meteorological variability which could obscure the effects of emission reduction were removed. A reduction of 4.8% in the 1980 eastern North American sulfur emissions was simulated by “turning off” one large source. This test resulted in estimated reductions of annually averaged sulfur wet deposition of between 15 and 1 % for stations separated from the source by 150–600 km.