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Concentration and Dry Deposition of Mercury Species in Arid South Central New Mexico (2001-2002)

U.S. Geological Survey, Biological Resources, New Mexico Cooperative Fish and Wildlife Research Unit, New Mexico State University, Box 30003, MSC 4901, Las Cruces, New Mexico 88003

Frontier GeoSciences, Inc., 414 Pontius Avenue North, Seattle, Washington 98109

This research was initiated to characterize atmospheric deposition of reactive gaseous mercury (RGM), particulate mercury (HgP; <2.5 m), and gaseous elemental mercury (Hg⁰) in the arid lands of south central New Mexico. Two methods were field-tested to estimate dry deposition of three mercury species. A manual speciation sampling train consisting of a KCl-coated denuder, 2.5 m quartz fiber filters, and gold-coated quartz traps and an ion-exchange membrane (as a passive surrogate surface) were deployed concurrently over 24-h intervals for an entire year. The mean 24-h atmospheric concentration for RGM was 6.8 pg m^-3 with an estimated deposition of 0.10 ng m^-2 h^-1. The estimated deposition of mercury to the passive surrogate surface was much greater (4.0 ng m^-2 h^-1) but demonstrated a diurnal pattern with elevated deposition from late afternoon to late evening (1400-2200; 8.0 ng m^-2 h^-1) and lowest deposition during the night just prior to sunrise (2200-0600; 1.7 ng m^-2 h^-1). The mean 24-h atmospheric concentrations for HgP and Hg⁰ were 1.52 pg m^-3 and 1.59 ng m^-3, respectively. Diurnal patterns were observed for RGM with atmospheric levels lowest during the night prior to sunrise (3.8 pg m^-3) and greater during the afternoon and early evening (8.9 pg m^-3). Discernible diurnal patterns were not observed for either HgP or Hg⁰. The total dry deposition of Hg was 5.9 g m^-2 year^-1 with the contribution from the three species as follows: RGM (0.88 g m^-2 year^-1), HgP (0.025 g m^-2 year^-1), and Hg⁰ (5.0 g m^-2 year^-1). The annual wet deposition for total mercury throughout the same collection duration was 4.2 g m^-2 year^-1, resulting in an estimated total deposition of 10.1 g m^-2 year^-1 for Hg. On one sampling date, enhanced HgP (12 pg m^-3) was observed due to emissions from a wildfire approximately 250 km to the east.