Four years of continuous total gaseous mercury (TGM) measurements at sites in Ontario, Canada

Total gaseous mercury (TGM) measurements have been conducted around the Great Lakes since 1997. At two of these sites (Egbert and Burnt Island), TGM concentrations presented significant seasonal variations. Possible explanations for the larger winter–spring/smaller summer–fall concentrations included seasonal meteorological differences, a northern hemispherical increase in coal combustion for wintertime heating, seasonal cycles of atmospheric oxidants and overall hemispherical source–sink relationship. The impact of populated/industrialized areas on the TGM concentrations at rural sites was demonstrated using pollution roses. Trend analyses for Egbert and Point Petre indicated relatively stable TGM concentrations between 1997 and 2000. Principal component analysis of TGM and trace metals confirmed the influence of the industrialized/populated area of Southwestern Ontario on both Egbert and Point Petre as well as metal recovery activities from Northern Ontario. For one episode of significant TGM concentrations, only a general geographical area could be implied as the source of atmospheric mercury.