Atmospheric Concentrations and Sources of Mercury to Western Maryland

Mark S. Castro1*, John Sherwell2 and Mark Cohen3

Since June 2005, we have been measuring the atmospheric concentrations of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (Hgp) in western Maryland. In this poster, we will present some of the important highlights our atmospheric mercury speciation data. For example, hourly averaged GEM concentrations ranged from 0.52 to 2.8 ng m-3, with an overall average of 1.45 ± 0.01 ng m-3. GEM exhibited statistically significant seasonal and diurnal variations. Seasonally averaged GEM concentrations ranged from 1.35 to 1.59 ng m-3. Summer (1.35 ± 0.02) and fall (1.39 + 0.01 ng m-3) had significantly (p<0.05) lower average GEM concentrations than winter (1.53 ± 0.04) and spring (1.59 + 0.02). There were statistically significant (p<0.05) variations in the hourly averaged GEM concentrations in the summer. Lowest hourly averaged GEM concentrations occurred between 3:00 AM (1.17 ± 0.04 ng m-3) and 6:00 AM (1.21 ± 0.03 ng m-3). From 6:00 AM to 9:00 AM, the hourly averaged GEM concentrations increased at a rate of 0.09 ng m-3 hr-1 until reaching the maximum value of 1.45 ± 0.02 ng m-3 at 9:00 AM. From 9:00 AM until 5:00 PM, the GEM concentrations were relatively constant, ranging between 1.41 and 1.45 ng m-3. Starting around 5:00 PM, the GEM concentrations slowly decreased until around 3:00 AM. Between 3:00 AM and 6:00 AM, the GEM concentrations were relatively stable at concentrations between 1.17 and 1.20 ng m-3. RGM concentrations ranged from below detection limits (BDL) to 119.3 pg m-3, with an overall average of 10.3 pg m-3. RGM exhibited strong seasonal variations with the greatest average concentration in spring (16.1 pg m-3), intermediate in summer and fall (9 pg m-3) and lowest in winter (6.8 pg m-3). In the summer and spring, RGM concentrations were statistically greater in the day than at night. Average particulate mercury Hgp concentrations ranged from BDL to 37.8 pg m-3, with an average of 5.1 pg m-3. Hgp exhibited strong seasonal variation with greatest concentrations in winter and fall and lowest concentrations in the other seasons. Hgp did not exhibit diurnal variations in any season. Back trajectory analyses using NOAA HYSPLIT suggested that mercury sources west and northwest of our monitoring station are the likely sources of RGM and Hgp.

1* Appalachian Laboratory, University of Maryland Center for Environmental Science, 301 Braddock Road, Frostburg, Maryland 21532, USA, 301 689-7163,
2 Power Plant Research Program, Maryland Department of Natural Resources, Tawes State Office Building, Annapolis, Maryland 21401, USA
3 NOAA Air Resources Laboratory, 1315 East West Highway, SSMC3, R/ARL, Room 3316, Silver Spring Maryland 20910, USA