Atmospheric Mercury Deposition In An Urban Environment

Atmospheric mercury deposition, known to be a major source of mercury to aquatic and terrestrial environments, was studied at an urban site in Orlando, FL. Precipitation sampling was conducted from September 2003 to May 2006 at a Mercury Deposition Network site located on the University of Central Florida campus. Weekly rainfall and mercury wet deposition data were gathered from this site, which provided the framework of data for this study. Historical mercury wet deposition data from several sites in Florida were used to develop a regression model to predict mercury deposition at any location in Florida. Stormwater runoff from a 2-acre impervious surface at this study area was monitored during the spring and summer of 2005. Runoff water quality was analyzed to characterize mercury dry deposition. Atmospheric monitoring was also conducted during this period to study the interaction of atmospheric constituents on wet and dry deposition patterns. Spatial and seasonal trends for the entire state suggest 80% of Florida\u27s rainfall and mercury deposition occur during the wet season. A strong linear correlation was established between rainfall depth and mercury deposition (R2 = 0.8). Prediction equations for the entire state, for both wet and dry seasons, were strongly correlated with measured data. The results of two unique methods to quantify dry deposition were similar at this site during this study period. Runoff monitored at this site contained significant levels of mercury, primarily in particulate form (58%). The vast majority of particulate mercury was flushed from the surface during storm events, while significant dissolved fractions remained. Runoff mercury concentrations were consistently higher than rainfall mercury, suggesting dry deposition accounted for 22% of total mercury in runoff. Atmospheric monitoring at this location showed gaseous elemental mercury was the dominant form (99.5%) followed by reactive gaseous mercury (0.3%) and particulate mercury (0.2%). Comparison of the contributions of wet and dry deposition suggested 80% of total mercury deposition was wet deposited during this study, while dry deposition accounted for the remaining 20%. Statistical correlations revealed rainfall scavenging of reactive gaseous mercury was the main factor controlling dry deposition