Spatial patterns in wet and dry deposition of atmospheric mercury and trace elements in central Illinois,USA

An intensive 1-month atmospheric sampling campaign was conducted concurrently at eight monitoring sites in central Illinois, USA, from June 9 to July 3, 2011 to assess spatial patterns in wet and dry deposition of mercury and other trace elements. Summed wet deposition of mercury ranged from 3.1 to 5.4 μg/m² across sites for the total study period, while summed dry deposition of reactive mercury (gaseous oxidized mercury plus particulate bound mercury) ranged from 0.7 to 1.6 μg/m², with no statistically significant differences found spatially between northern and southern sites. Ratios of summed wet to summed dry mercury deposition across sites ranged from 2.2 to 4.9 indicating that wet deposition of mercury was dominant during the study period. Volume-weighted mean mercury concentrations in precipitation were found to be significantly higher at northern sites, while precipitation depth was significantly higher at southern sites. These results showed that substantial amounts of mercury deposition, especially wet deposition, occurred during the study period relative to typical annual wet deposition levels. Summed wet deposition of anthropogenic trace elements was much higher, compared to summed dry deposition, for sulfur, selenium, and copper, while at some sites summed dry deposition dominated summed wet deposition for lead and zinc. This study highlights that while wet deposition of Hg was dominant during this spring/summer-season study, Hg dry deposition also contributed an important fraction and should be considered for implementation in future Hg deposition monitoring studies.