The model scheme of HM behaviour in the atmosphere

Mercury enters the atmosphere from anthropogenic and natural sources. They include point (coal-fired power plants, waste incinerators, volcanoes etc.) and diffuse area sources (mill tailings, municipal wastes, geologically enriched soils) [Jackson, 1997; Gustin et al., 1999]. Whereas anthropogenic emissions contain a number of mercury species (elemental mercury vapour, oxidized gaseous and particulate mercury), natural emissions mostly consist of elemental vapour. Moreover, mercury vapour is emitted to the atmosphere from the sea surface due to marine biota activity [Kim and Fitzgerald, 1986].

Once emitted to the atmosphere mercury is transported through it with the air masses (advective transport) and dispersed by eddy diffusion. During the pathway in the atmosphere mercury species under go physical and chemical transformations resulting in their mutual redistribution. Thus, elemental mercury is oxidized by such oxidants as ozone and OH radical. Besides, it is dissolved in cloud water and takes part in aqueous-phase oxidation and reduction reactions, formation of sulphite and chloride complexes, which are in turn adsorbed by soot particles. Mercury species are removed from the atmosphere by means of surface uptake and precipitation scavenging.