Patterns of Atmospheric Elemental and Reactive Gaseous Hg Concentrations in the Central and Eastern United States: Comparison of Inland and Coastal Sites

Since 2003 we have conducted multiple sampling campaigns, several weeks to a year in duration, to measure concentrations of atmospheric mercury (Hg) species at several sites in the central and eastern United States. The studies have been completed to better understand the impact of atmospheric Hg on terrestrial and aquatic environments. Sites sampled range from heavily industrialized areas (East St. Louis, MO and Milwaukee, WI) to remote locations (Cabezas de San Juan, Puerto Rico) and include both coastal (Weeks Bay, AL and Cape Romain, SC) and inland settings (Lostwood, ND; Devil's Lake, WI; and Big Meadows. VA).

Quarterly elemental Hg concentrations at these 8 sites range from 1.27±0.31 to 2.94±1.57 ng m^-3 and are greatest during the spring and winter and at sites near large local Hg sources. The seasonal variability may result from changes in emissions, boundary layer formation, and/or Hg deposition velocity. Concentrations of reactive gaseous mercury (RGM) range from 1.5±1.6 to 63.2±528 pg m^-3; the season exhibiting the highest RGM concentrations differs among sites. The highest RGM concentrations are associated with heavily industrialized sites (East St. Louis and Milwaukee) and follow an erratic diel pattern indicative of short-lived plumes from local sources. Strong diel patterns with early afternoon maximum RGM concentrations were observed at two coastal sites (Weeks Bay, AL and Cape Romain, SC). These patterns are indicative of photochemical RGM production.

To estimate dry deposition of Hg species at each site, a resistance model based on meteorology and canopy cover for each location will be used. These model estimates will be compared to nearby wet deposition and emission data to examine the influence of regional sources on deposition rates. Findings from this study highlight the importance of location and environmental setting on the magnitude of atmospheric Hg deposition.