Predicting the fate and transport of toxic metal emissions over the United States.

Anthropogenic emissions are believed to determine the atmospheric concentrations and deposition of several metals present in particulate mater. Several of these metals have toxic effects on human health. Because of such effects, the United States Environmental Protection Agency (EPA) reports metallic emissions in their National Emissions Inventory (NEI) to assess risks to human health. To better understand where and when humans are exposed to the highest levels of toxic metals, we have developed a regional model for the transport and fate of six metals (lead, nickel, chromium, cadmium, beryllium and manganese) reported by the NEI. An application used the NEI for 1999 and predicted the atmospheric concentrations, as well as deposition over the continental United States (US). Results show that concentrations are two to three orders of magnitude greater over the US than over remote marine locations. The result roughly agrees with observations reported by US monitoring sites during 2001. Highest predicted concentrations occur over northeastern states and the lower Mississippi river. Deposition of toxic metals has a strong spatial gradient, and a strong seasonal component. Disclaimer: The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) and under agreement number DW13921548. This work constitutes a contribution to the NOAA Air Quality Program. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect their policies or views.