The chemistry of atmospheric mercury: a review

The atmosphere is an important transient reservoir of mercury. In addition to its great capacity, the chemical processes transforming mercury between the elemental and divalent states strongly influence the transport characteristics and deposition rate of this toxic metal back to the ground. Modeling efforts to assess global cycling of mercury require an in-depth knowledge of atmospheric mercury chemistry. This provides selected physical and chemical properties of atmospheric mercury, and discusses the identified mercury transformation pathways mediated by ozone, S(IV), hydroperoxyl radical, hydroxyl radical, chlorine, nitrate radical and photolysis of Hg(II) complexes. Special attention is paid to the kinetics and mechanisms of the reactions interconverting mercury between elemental and divalent states. The significance and implications of each transformation pathway under atmospheric conditions are addressed. Future research areas that must be pursued to better understand the fate and transformation of mercury in the atmosphere are also projected.