Estimated Trends in Wet Mercury Deposition at MDN Sites

Dr. Kevin Civerolo and Gopal Sistla
New York State Department of Environmental Conservation Division of Air Resources
625 Broadway, 2nd Floor, Albany, NY 12233-3259

With the proposed reductions in mercury EGU emissions in the coming years, it is instructive to examine current trends in mercury wet deposition. To this end we used the nonparametric Seasonal Kendall test to estimate trends at 49 MDN sites having at least seven years of data. Preliminary analysis suggests that 18 sites experienced statistically significant declines in mercury concentrations in wet deposition, despite the fact that trends in precipitation at these sites, although generally not significant, were found to be increasing at 31 of the 49 sites. There does not appear to be any clear geographic pattern to these significant declines, as these 18 sites were distributed across the MDN network. Changes in mercury deposition will be compared with changes in sulfate deposition at these locations. It will be important to continue this analysis as more data become available and more sites are brought on-line to assess the impacts of the Clean Air Mercury Rule and other emissions reductions programs over the next decade.