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 mu m), and gaseous elemental mercury (Hg-0) 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 mu 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 Hg-0 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 Hg-0. The total dry deposition of Hg was 5.9 mu g m(-2) year(-1) with the contribution from the three species as follows: RGM (0.88 mu g m(-2) year(-1)), HgP (0.025 mu g m(-2) year(-1)), and Hg-0 (5.0 mu g m(-2) year(-1)). The annual wet deposition for total mercury throughout the same collection duration was 4.2 mu g m(-2) year(-1), resulting in an estimated total deposition of 10.1 mu 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.