Atmospheric deposition of nitrogen, sulphur, and mercury negatively impact Pacific Northwest aquatic and terrestrial ecosystems. Therefore, a better understanding of the various atmospheric processes and pathways involving deposition of nitrogen, sulphur, and mercury is critical to environmental policy decisions. Excess atmospheric deposition of nitrogen and sulfur in soil and water systems can lead to increases in acidification and changes in nutrient cycles and storage that negatively impact biodiversity here in the Pacific Northwest. Atmospheric deposition of mercury in southern Idaho has come under increased scrutiny with the addition of fish consumption advisories in several reservoirs and riverine environments.

The AIRPACT-3 modeling system has been used to simulate nitrogen, sulphur, and mercury atmospheric deposition in the Pacific Northwest in order to address growing regional interest in atmospheric deposition patterns of these species. The model was run for a 12-km gridded domain. The domain coverage area (rectangular) extends from southern British Columbia to northern California and from the Pacific shoreline to western Montana. The modeling system uses MM5 meteorology, SMOKE-based emissions, and a modified version of CMAQ that handles additional mercury chemistry. An overview of how AIRPACT-3 models dry and wet deposition of nitrogen, sulphur, and mercury will be presented. Analysis of deposition patterns for each species will be discussed. Model and observation comparisons will also be presented.