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 (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 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 -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 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 Hg 0 (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.