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

A Kolker,M A Engle,M T Tate,M L Olson,D P Krabbenhoft

doi:10.5194/acp-10-4467-2010

A Kolker, M A Engle + Show 3 more

Open Access

https://doi.org/10.5194/acp-10-4467-2010

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Abstract

Abstract. Simultaneous real-time changes in mercury (Hg) speciation- reactive gaseous Hg (RGM), elemental Hg (Hg°), and fine particulate Hg (Hg-PM2.5), 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-PM2.5, and RGM were positioned at distances of 25, 50 and 100 km northward of the larger electric utility. Median concentrations of Hg°, Hg-PM2.5, and RGM were 1.3–1.4 ng m−3, 2.6–5.0 pg m−3, and 0.6–0.8 pg m−3, 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 m-3) measured at the 100 km site, and corresponding elevated SO2 (10.4 ppbv; measured at 50 km site). The finding that RGM, Hg°, and Hg-PM2.5 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.

Highlights

Atmospheric emissions, transport and deposition of mercury (Hg) are key processes leading to the global mercury contamination problem (Wiener et al, 2003)
Using this three-receptor array, changes in mercury speciation were continuously monitored, showing the influence of three Hg emission sources located at the periphery of the study area in opposing directions (Fig. 1), as well as regional sources from major urban areas of the US Midwest
To determine Hg speciation, RGM is sequentially collected on a KCl-coated annular denuder, fine particulate Hg-PM2.5 is collected on a re-generable particulate filter and Hg◦ is collected on gold traps

Summary

Introduction

Atmospheric emissions, transport and deposition of mercury (Hg) are key processes leading to the global mercury contamination problem (Wiener et al, 2003). Speciation of atmospheric mercury is influenced by a combination of local emission sources, generally contributing a greater proportion of reactive species, and global long range transport of long lived species such as Hg◦. We set up three receptor stations at different locations within a rural study area having no major anthropogenic Hg emission sources within 25 km or more. Using this three-receptor array, changes in mercury speciation were continuously monitored, showing the influence of three Hg emission sources located at the periphery of the study area in opposing directions (Fig. 1), as well as regional sources from major urban areas of the US Midwest. The goals of the study were to: 1) distinguish multiple Hg inputs in a rural setting with relatively few Hg sources, that are directionally distinct; 2) track possible conversion between atmospheric Hg species; and 3) test the efficacy of simultaneous deployment of mercury speciation monitoring stations for possible use by the National Atmospheric Deposition Program (NADP) Atmospheric Mercury Network (AMNet)

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