Our previous work has documented a correlation between Hg concentrations and 210Pb activity measured in wet deposition that might be used to help apportion sources of Hg in precipitation. Here we present the results of a 27-month precipitation collection effort using co-located samplers for Hg and 210Pb designed to assess this hypothesis. Study sites were located on the east and west coasts of North America, in the continental interior, and on the Florida Peninsula. Relatively high variability in Hg/210Pb ratios was found at all sites regionally and seasonally (e.g., overall: 0.99-9.13ngdpm-1). The ratio of average volume-weighted Hg concentrations and 210Pb activities showed consistent trends (higher in impacted area), with Glacier Bay in southeast Alaska, exhibiting the lowest value. Assuming that Glacier Bay represents a benchmark for a site with no regional contribution, we estimate less than 50% of the Hg input was "global" at the Seattle and Florida sites. Differences in Hg/210Pb in wet deposition could be due to either a regional/local source contribution of Hg, or a regional/local enhancement in the removal of Hg from the atmosphere (i.e., oxidants), however, this approach is not capable of discerning between these two possibilities. Thus, this method of source apportionment represents an estimate of the maximal amount of Hg contributed by regional sources and may be limited in regions of deep convective mixing.
Bibliographical noteFunding Information:
Laboratory assistance at UConn was provided by Larissa Graham, Allan Hutchins, Jillian Weber, and Ming Chung. Our thanks to Erin Mortensen and Jill Coleman at the Science Museum of MN, SCWRS. Our program benefited from interested colleagues associated with current operations and facilities (National Parks, and the MDN sites), and their cooperation was needed for efficient access to remote lakes and watersheds. We wish to thank Rob Tordon and Steve Beauchamp (Environment Canada, Nova Scotia) and Hazel Crocker (Newfoundland); David Manski, Bob Breen, and Emily Seger (Acadia National Park); Larry Fink, Mark Kromer, Joseph Jean-Jacques, and Nichole Niemeyer (S. Florida Water Management District); Ed Swain (Minnesota Pollution Control Agency), Deacon Kyllander and Art Elling (U.S. Forest Service, MN), and Lee Klossner and LaMoine Nickel (University of Minnesota); Bob Brunette, Megan Voigt, Nicholas McMillan, and Kirsi Longley (Frontier Geosciences, WA); Rusty Yerxa and Mary Kralovec (Glacier Bay National Park, AK). We are grateful for the support provided by the U.S. Environmental Protection Agency through a STAR Research Grant ( R829796 ). The work, however, does not necessarily reflect the views of the U.S. EPA, and no official endorsement should be inferred.
- Mercury deposition network
- National atmospheric deposition network
- Source apportionment