Local and regional factors affecting atmospheric mercury speciation at a remote location

Atmospheric concentrations of elemental (Hg⁰), reactive gaseous (RGM), and particulate (PHg) mercury were measured at two remote sites in the midwestern United States. Concurrent measurements of Hg⁰, PHg, and RGM obtained at Devil’s Lake and Mt. Horeb, located approximately 65 km apart, showed that Hg⁰ and PHg concentrations were affected by regional, as well as local sources, while RGM was mainly impacted by local sources. Plumes reaching the Devil’s Lake site from a nearby coal-fired power plant significantly impacted SO₂ and RGM concentrations at Devil’s Lake, but had little impact on Hg⁰. Our findings suggest that traditional modeling approaches to assess sources of mercury deposited that utilize source emissions and large-scale grids may not be sufficient to predict mercury deposition at sensitive locations due to the importance of small-scale sources and processes. We suggest the use of a receptor-based monitoring to better understand mercury source–receptor relationships.