Concentration and dry deposition of mercury species in arid south central New Mexico (2001-2002)

This research was initiated to characterize atmospheric deposition of reactive gaseous mercury (RGM), particulate mercury (HgP; <2.5 μm), 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 μm 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^-2h^-1. The estimated deposition of mercury to the passive surrogate surface was much greater (4.0 ng m^-2h^-1) but demonstrated a diurnal pattern with elevated deposition from late afternoon to late evening (1400−2200; 8.0 ng m^-2h^-1) and lowest deposition during the night just prior to sunrise (2200−0600; 1.7 ng m^-2h^-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 μg m^-2 year-1 with the contribution from the three species as follows:  RGM (0.88 μg m^-2 year^-1), HgP (0.025 μg m^-2 year^-1), and Hg⁰ (5.0 μg m^-2 year^-1). The annual wet deposition for total mercury throughout the same collection duration was 4.2 μg m^-2 year^-1, resulting in an estimated total deposition of 10.1 μg 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.