Patterns of mercury dispersion from local and regional emission sources, rural Central Wisconsin, USA

摘要

pstrongAbstract./strong Simultaneous real-time changes in mercury (Hg) speciation- reactive gaseous Hg (RGM), elemental Hg (Hg?°), and fine particulate Hg (Hg-PMsub2.5/sub), were determined from June to November, 2007, in ambient air at three locations in rural Central Wisconsin. Known Hg emission sources within the airshed of the monitoring sites include 1) a 1114 megawatt (MW) coal-fired electric utility generating station; 2) a Hg-bed chlor-alkali plant; and 3) a smaller (465 MW) coal-burning electric utility. Monitoring sites, showing sporadic elevation of Hg?°, Hg-PMsub2.5/sub, and RGM were positioned at distances of 25, 50 and 100 km northward of the larger electric utility. Median concentrations of Hg?°, Hg-PMsub2.5/sub, and RGM were 1.3a??1.4 ng msupa??3/sup, 2.6a??5.0 pg msupa??3/sup, and 0.6a??0.8 pg msupa??3/sup, respectively. A series of RGM events were recorded at each site. The largest, on 23 September, occurred under prevailing southerly winds, with a maximum RGM value (56.8 pg msup-3/sup) measured at the 100 km site, and corresponding elevated SOsub2/sub (10.4 ppbv; measured at 50 km site). The finding that RGM, Hg?°, and Hg-PMsub2.5/sub are not always highest at the 25 km site, closest to the large generating station, contradicts the idea that RGM decreases with distance from a large point source. This may be explained if 1) the 100 km site was influenced by emissions from the chlor-alkali facility or by RGM from regional urban sources; 2) the emission stack height of the larger power plant promoted plume transport at an elevation where the Hg is carried over the closest site; or 3) RGM was being generated in the plume through oxidation of Hg?°. Operational changes at each emitter since 2007 should reduce their Hg output, potentially allowing quantification of the environmental benefit in future studies./p.