Calculation of visual range improvements from SO sub(2) emission controls - II. An application to the Eastern United States

This paper, the second of a two-part series, presents an application of a new semi-empirical methodology to assess the annual average improvements in visual range that can be expected from a reduction of SO sub(2), emissions in the eastern United States. This semi-empirical methodology was described in Part 1 of the series (Zannetti et al., Atmospheric Environment 24A, 2361-2368, 1990). As an illustrative example of its application, we calculate here the visibility improvements expected from a 12 million-tons yr super(-1) SO sub(2), emission reduction scenario (a reduction of about 55% from 1980 emissions) in the 31 eastern states. We find that reduction of this size would generate improvements in visual range that, as regional annual averages over eight subregions throughout the eastern United States, vary from 8%(6; 11) to 11%(9; 15), where the two numbers between parentheses indicate "lower" and "upper" estimates, respectively, defined as plus/minus one standard deviation in a probability distribution. Thus, the relative visibility improvements are much smaller than the relative SO sub(2) emission reduction, with an "efficiency" (i.e. per cent visual range improvement divided by per cent emission reduction) that varies regionally from 0.15 (0.11; 0.20) to 0.21 (0.15; 0.28).