| Description |
Two years of speciated atmospheric mercury data in the Intermountain West are examined for annual, seasonal, and diurnal patterns, as well as influences of precipitation. Mercury is a pollutant in the atmosphere that occurs as three species: gaseous elemental mercury (GEM), particulate-bound mercury (PBM), and gaseous oxidized mercury (GOM). Mercury can enter ecosystems from the atmosphere via wet and dry deposition. In aquatic ecosystems, it can convert to the neurotoxin methylmercury, which has prompted consumption advisories for both fish and waterfowl. A Tekran ambient air mercury monitor was deployed at a site (UT96) near the Great Salt Lake, Utah as part of the Atmospheric Mercury Network (AMNet). UT96 has the only such detector in continuous operation in Utah with two years of data (July 2009 - June 2011). All three mercury species exhibit right-skewed distributions and vary in concentration over multiple orders of magnitude. GEM is the dominant species with a median concentration of 1.58 ng m-3 (range 0.25 - 64.47 ng m-3). PBM has a median concentration of 5.7 pg m-3 (range 0 - 803.2 pg m-3), while GOM has a median concentration of 2.6 pg m-3 (range 0 - 225.6 pg m-3). The sporadic nature of the extremely high GEM and PBM events suggest that they primarily result from local/regional emissions. In contrast, extremely high GOM events depend strongly on time of day and season, suggesting a connection to meteorological conditions. All three species exhibit statistically significant seasonal and diurnal patterns. GOM exhibits the strongest seasonal pattern, peaking during summer with median summer concentrations a factor of six greater than median winter concentrations. GEM and PBM peak during winter. All three species exhibit statistically significant diurnal patterns for at least part of the year. GOM has the most pronounced diurnal cycle, particularly during summer.Median concentrations of GOM during the afternoons of summer months are greater than 20 pg m-3, while median concentrations overnight are below 5 pg m-3. GEM and PBM both exhibit minima in concentrations during the afternoons, and both exhibit the largest diurnal variation amplitude during summer. Neither GEM nor PBM exhibit a statistically significant diurnal pattern during winter. An examination of the influences of precipitation on mercury concentrations indicates that precipitation scavenges GOM more efficiently than PBM, and that the scavenging increases as the amount of precipitation increases. Mixed precipitation scavenges PBM better than either rain or snow alone. The median GOM concentration during rain, snow, and mixed precipitation were all below the method detection limit (MDL), and could not be distinguished. There are some indications in the data that rain may promote slightly elevated concentrations of GEM. |
