Temporal patterns of speciated atmospheric mercury measurements in Utah

Two years of speciated atmospheric mercury data in the Intermountain West are examined for annual, seasonal, and diurnal patterns. 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). 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 concentrations of all three species vary by season. GOM exhibits the strongest seasonal pattern, peaking during summer with median summer concentrations a factor of 6 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 concentration during the afternoons, and both exhibit the largest amplitude in diurnal variation during summer. Neither GEM nor PBM exhibit a statistically significant diurnal pattern during winter. The sporadic nature of the extremely high GEM and PBM events suggests that they primarily result from local/regional emissions, while extremely high GOM events depend strongly on time of day and season, suggesting a connection to meteorological conditions.