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National-scale assessment of total gaseous mercury isotopes across the United States

April 12, 2023

With the 2011 promulgation of the Mercury and Air Toxics Standards by the U.S. Environmental Protection Agency, and the successful negotiation by the United Nations Environment Program of the Minamata Convention, emissions of mercury (Hg) have declined in the United States. While the declines in atmospheric Hg concentrations in North America are encouraging, linking the declines to changing domestic and global source portfolios remains challenging. To address these research gaps, the U.S. Geological Survey initiated the first national-scale effort to establish a baseline of total gaseous mercury stable isotope values at 31 sites distributed across the United States. Results indicated that unique Hg sources, such as Hg evasion from an elemental Hg contaminated site or free tropospheric intrusions in high altitude sites, were distinguishable from background atmospheric values. Minor gradients were observed across the nation, with regions of heavy industrial activity demonstrating lower δ202Hg, but no consistent changes in other isotopes such as Δ199Hg and Δ200Hg were observed. Furthermore, δ202Hg was impacted by foliar uptake and senescence but trends varied between forested regions in the northeastern and midwestern United States. These data demonstrate regional emission sources and other environmental variables can impact total gaseous Hg (TGM) isotope values, highlighting the need to characterize atmospheric Hg isotopes over larger geographical areas to evaluate changes related to national and international Hg regulations.

Publication Year 2023
Title National-scale assessment of total gaseous mercury isotopes across the United States
DOI 10.1029/2022JD038276
Authors Michael T. Tate, Sarah E. Janssen, Ryan F. Lepak, Laura Elizabeth Flucke, David P. Krabbenhoft
Publication Type Article
Publication Subtype Journal Article
Series Title JGR Atmospheres
Index ID 70243217
Record Source USGS Publications Warehouse
USGS Organization Wisconsin Water Science Center; Upper Midwest Water Science Center