Temporal and spatial variability of total gaseous mercury in Canada: results from the Canadian Atmospheric Mercury Measurement Network (CAMNet)

Continuous measurements of total gaseous mercury (TGM) concentration were taken during 1997–1999 at 10 rural sites across Canada, ranging from 43° to 82°N and from 62° to 123°W. Overall median TGM concentrations ranged among the sites from 1.32 to 1.83 ng m−3. The spatially averaged median concentration among all sites was 1.60±0.15 ng m−3. Maximum hourly average concentrations, on the order of 10 ng m−3, were observed at several sites located near major sources of anthropogenic emissions. Minimum hourly average concentrations were observed in springtime at the arctic site where concentrations dropped below the detection limit of the analyzer (50 pg m−3) on several occasions. Seasonal variability in TGM concentrations was observed at all sites. At most sites monthly median concentrations were highest in late winter and lowest in fall. Diurnal variations in TGM concentration were also observed at most sites. The most common pattern of diurnal variability was a diel cycle of minimum concentrations just before sunrise and maximum concentrations around solar noon. The diel cycle was seasonally modulated, reaching maximum amplitude during spring or summer at all sites.