Atmospheric deposition of mercury, trace elements, and major ions around a coal-fired power plant (3002001018)

This report describes the results of a multiyear study to measure mercury (Hg), trace elements, and major ions in precipitation around Plant Crist, a four-unit coal-fired power plant in Pensacola, Florida. The main purpose of the study was to see if Hg emissions from Plant Crist could be detected and quantified in local wet deposition. Specifically, the study evaluated whether the significant reduction in Hg emissions that accompanied the installation of a wet flue gas desulfurization scrubber system in December 2009 resulted in observable decreases in nearby Hg deposition. Statistical analyses of precipitation data from three to four sites for November 19, 2004, to March 31, 2012, showed no significant increase or decrease in Hg concentrations, despite year-to-year differences. In contrast, significant declines in both the concentration and deposition of nitrate and non-sea salt sulfate occurred over the seven-year study period. Monthly volume weighted Hg concentrations, as well as Hg deposition, were generally higher during the warm season. These and other observations are consistent with the hypothesis that long-range transport brings air masses with elevated levels of reactive gaseous Hg and/or aerosol Hg to the Pensacola area during the warm season. A “first order” source-receptor analysis for Hg attributed 4%–34% of Hg wet deposition in the Pensacola area to coal combustion–related emissions. The estimated attribution did not change significantly after the installation of the scrubber system at Plant Crist in December, 2009, thus indicating that Plant Crist had no significant impact on Hg wet deposition in the region either pre- or postscrubberTechnical ReportFinal repor