| Description |
A growing problem in the western United States is the widespread contamination of remote lakes by the atmospheric transport and deposition of mercury (Hg). In this study, we measured gaseous elemental Hg (GEM), reactive gaseous Hg (RGM), and particulate Hg (HgP) with a Tekran® system near Salmon Falls Creek Reservoir (SFCR) in south-central Idaho. These measurements were made during a series of 1 -month long, intensive operation periods (IOPs) in the winter, spring, summer, and fall of 2008. Each IOP consisted of coincident size- and time-resolved aerosol elemental composition measurements that were made using an 8-stage rotating drum impactor and analyzed by synchrotron X-ray fluorescence. The Positive Matrix Factorization (PMF) receptor model was then applied to the high-resolution, aerosol elemental composition data from each IOP to determine source types and profiles. A stepwise multiple linear regression technique was then used to apportion the Hg concentrations to the source types identified by the PMF analysis. Using the Hybrid Single-Particle Lagrangian Integrated Trajectory model, we analyzed reverse trajectories during peak Hg concentrations to identify source regions. GEM was the most prominent atmospheric species (>99% of total Hg) and the global background GEM contributed -90% of the total Hg. Mining operation sources were the most significant regional GEM source and had its largest contributions during the winter (80% of the regional GEM). Biomass burning was a strongly seasonal source of GEM, but was able to significantly contribute during 2 biomass episodes during the summer. GEM-rich airmasses primarily approached the site from the west and southwest and indicate that mining sources are consistent contributors during all seasons. Approximately 75% of the total RGM observed was a result of diurnal processes (e.g., convective mixing with free troposphere, atmospheric oxidation of GEM). Mining operation sources, Asian transport, and biomass burning comprised the remaining 25% of RGM from regional/global sources. RGM-rich trajectories primarily approached SFCR from the southwest during all but 1 season (spring). |
