This study had been carried out in downtown Toronto from December 2003 to November 2004. Gaseous elemental mercury (GEM), reactive gaseous mercury (RGM, also called gaseous oxidized inorganic mercury, GOIM) and mercury associated with particles having size (PM<2.5) were simultaneously measured using Tekran mercury speciation unit. Mean concentration, standard deviation and distribution of GEM, PM<2.5 and RGM were 4.52 +/- 3.13 ng m⁻³ (98.7%), 21.51 +/- 16.35 pg m⁻³ (0.5%) and 14.19 +/- 13.24 pg m⁻³ (0.3%), respectively. Local and regional anthropogenic sources are believed to contribute [to] the elevated value and high temporal variations. Overall, the mercury species concentrations are lower in winter than in the other three seasons. Nighttime GEM, PM<2.5 and RGM concentrations are higher than those of daytime. Correlation analysis was conducted between each mercury species and the meteorological parameters (i.e., surface ambient air temperature, relative humidity, wind direction), as well as among the mercury species in this study.