MODELING THE ATMOSPHERIC MERCURY CYCLE - CHEMISTRY IN FOG DROPLETS

A model has been developed describing the mass transport and chemistry of different forms of mercury in the atmosphere (the CAM model). 48-h our simulations of an air parcel containing a fog have been used to ex amine the influence of a number of chemical parameters on dissolved di valent mercury, Hg(II), in fog droplets. Representation of chlorine ch emistry was found to be very important for modelling of mercury specie s, as mercury-chloride complexes dominate the dissolved Hg(II) fractio n in competition with the reactive Hg(II)-S(IV) complexes. If the pH i s increased, the importance of HgCl2 will decrease in favour of Hg(II) -S(IV) complexes which, in turn, will lead to lowered concentrations o f dissolved Hg(II)), due to an enhanced production of volatile Hg-0 vi a reduction of HgSO3. At low SO2 concentration (0.5 < SO2 < 10 ppb) di ssolved mercury is strongly inversely dependent on the gas phase SO2 c oncentration. The ozone concentration is almost linearly related to th e dissolved Hg(II) content. Total mercury content (dissolved plus adso rbed Hg(II)) is strongly correlated to soot concentration. At high soo t concentrations all Hg(II) is expected to be found in the adsorbed fo rm.