FIELD OBSERVATIONS OF TOTAL GASEOUS MERCURY BEHAVIOR - INTERACTIONS WITH OZONE CONCENTRATION AND WATER-VAPOR MIXING-RATIO IN AIR AT A RURALSITE

Total Gaseous Mercury (TGM) data (n = 5125) measured from September 9 to November 30, 1994 in Southern Quebec with an automatic TGM analyser (Tekran(R)) are used to study the behaviour of TGM with ozone and the water vapour mixing ratio. Results show, as a whole, no straight-forw ard correlation between TGM and ozone concentrations. A significant co rrelation between TGM and water vapour mixing ratio was measured. Some back reduction of Hg(II) to Hg degrees in the aqueous phase and subse quent evaporation of Hg degrees 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 vap our mixing ratio is twice that during 'polluted conditions' (ozone gre ater than or equal to 30 ppbv) which suggests some compensation effect s under polluted conditions (counteracting the back-reduction of Hg(TT ) to Hg degrees in the aqueous phase). Oxidation of TGM by ozone durin g high moisture conditions (water vapour mixing ratio similar to 14g/k g) seems to appear at the threshold ozone concentration greater than o r equal to 30 ppbv.