Atmospheric gaseous elemental mercury in downtown Toronto

Continuous measurements of gaseous elemental mercury (GEM) in downtown Toronto were conducted from June 2001–February 2002. Ambient air was sampled at 3.5 and 7 m above ground in a canopy over a sidewalk. The quarter hourly mean concentrations were found at 2.39±2.05 ng m−3 (N=10,658) for the lower sampling level, and 2.57±2.39 ng m−3 (N=10,628) for the upper sampling level. The average of both sampling levels (2.48 ng m−3) was 60% higher than the average of Canadian background emission (1.55 ng m−3, Alert). Seasonal concentrations showed the effects of the temperature on the volatilization of Hg0. Higher GEM was found in the summer time (20 June–19 September) at 3.03±2.13 ng m−3 (lower level) and 3.31±2.56 ng m−3 (upper level) while lower values were observed in the fall (20 September–19 December) at 1.84±0.87 ng m−3 (lower level) and 1.97±1.38 ng m−3 (upper level). Log normal probability distribution of the GEM concentration was verified and the double peak hourly average diurnal distribution of GEM concentration was observed in our study.