A year of continuous measurements of three atmospheric mercury species (GEM, RGM and Hgp) in southern Québec, Canada

An intensive field campaign was conducted from 1 January to 31 December 2003 in St. Anicet (Québec, Canada) using a set of Automatic Atmospheric Mercury Speciation Analyzers (Tekran 2537A with 1130 and 1135 units) for the measurements of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (Hgp). This study is one of the first attempts to present the most extensive data sets of a year of continuous measurements of atmospheric mercury species. Average concentrations of GEM, RGM and Hgp in 2003 were 1.65±0.42 ng m−3, 3±11 and 26±54 pg m−3 (mean±SD), respectively. On an average, the atmospheric mercury apportioned as follows: GEM (98.4%)>Hgp (1.4%)>RGM (0.2%). Regional atmospheric mercury sources contributed to the Southern Québec atmospheric mercury contamination. The results showed large seasonality of GEM, RGM and Hgp (GEM: 0.37-10.4 ng m−3; RGM: 0-386 pg m−3 and Hgp: 0-1528 pg m−3). As a whole, mercury speciation concentrations are larger in wintertime than in summertime. RGM and Hgp concentrations showed the sharpest seasonal variations. Hourly variations were observed for the mercury species. Maximum RGM and Hgp concentrations were measured normally during mid-day with a Gaussian shape whereas GEM showed a bimodal shape with minimum values early in the morning. The backward trajectory model showed that atmospheric mercury speciation might be transported from local or regional sources. Also, it was observed that atmospheric mercury transformation times converting GEM to Hgp were short (∼4 h). However, atmospheric kinetics involving O3 and OH radicals do not support such fast oxidation processes with normal concentrations.