FIELD OBSERVATIONS OF TOTAL GASEOUS MERCURY BEHAVIOUR: INTERACTIONS WITH OZONE CONCENTRATION AND WATER VAPOUR MIXING RATIO IN AIR AT A RURAL SITE

Total Gaseous Mercury (TGM) data (n = 5125) measured from September 9 to November 30, 1994 in Southern Québec with an automatic TGM analyser (Tekran®) are used to study the behaviour of TGM with ozone and the water vapour mixing ratio. Results show, as a whole, no straight-forward correlation between TGM and ozone concentrations. A significant correlation between TGM and water vapour mixing ratio was measured. Some back reduction of Hg(II) to Hg° in the aqueous phase and subsequent evaporation of Hg° according to Henry‘s Law is expected. The latter correlation seems to be partly ozone dependent since under ’clean conditions‘ (ozone < 30 ppbv) the slope of TGM vs the water vapour mixing ratio is twice that during ‘polluted conditions’ (ozone ≥ 30 ppbv) which suggests some compensation effects under polluted conditions (counteracting the back-reduction of Hg(II) to Hg° in the aqueous phase). Oxidation of TGM by ozone during high moisture conditions (water vapour mixing ratio ～14g/kg) seems to appear at the threshold ozone concentration ≥ 30 ppbv.