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National-scale assessment of total gaseous mercury isotopes across the United States
Citation:
Tate, M., S. Janssen, R. Lepak, L. Fluke, AND D. Krabbenhoft. National-scale assessment of total gaseous mercury isotopes across the United States. JOURNAL OF GEOPHYSICAL RESEARCH: ATMOSPHERES. American Geophysical Union, Washington, DC, 128(8):N/A, (2023). https://doi.org/10.1029/2022JD038276
Impact/Purpose:
A simple, economic total gaseous mercury analyzer was deployed across the United States to determine if atmospheric sources of mercury were distinguishable across regions and seasons using the mercury stable isotope method. Results indicated that heavily contaminated sites and high elevation sites did have different mercury isotope values, but overall values across the country were similar. Further application of these measurements may aid in assessing the impact and changing sources of mercury within site- specific studies as a result of federal and global initiatives, including the Minamata Convention on Mercury.
Description:
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 Programme of the Minamata Convention, global emissions of mercury (Hg) have declined in North America. While the declines in atmospheric concentrations in North America are encouraging, linking the declines to actions taken domestically and overseas remains complex. Then domestically, tracking the impact of sector-specific emission-reductions is challenging without improved tools. To address these challenges, the U.S. Geological Survey, and the National Atmospheric Deposition Program (NADP) initiated a national-scale effort to establish a baseline of total gaseous mercury (TGM) and Hg stable isotopic compositions 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 ¿202Hg, but no consistent changes in other isotopes such as ¿199Hg and ¿200Hg were observed. Furthermore, ¿202Hg was impacted by foliar uptake and senescence but trends varied between forested regions in the Northeastern and Midwestern United States. These data demonstrate the relative consistency in TGM isotope values measured across a wide range of sites yet also point to nuance associated with regional emission sources and other environmental variables, highlighting the need to characterize atmospheric Hg isotope pools over larger geographical areas.
URLs/Downloads:
DOI: National-scale assessment of total gaseous mercury isotopes across the United States