Speciation of metals in the atmosphere

The atmospheric input of trace metals to the oceans has now been recognised to be of considerable importance to the marine system. Riverine sources have, for many years, been thought to be the dominant input route for metals into the oceans. Recent studies show, however, that these terrestrial fluxes may be equalled or even exceeded by inputs from the atmosphere. Thus, because of the importance of atmospheric input to the oceans, many of the examples considered here will focus on metal speciation in remote marine areas. In Table 7.1, average metal values in aerosols and rain at several sites are reported to show the range of concentrations of interest. 

Direct comparison of the atmospheric and riverine modes of input to the oceans can be misleading because of differences which act to maximise the importance of the atmospheric input route  

Element Aerosol concentrations (nmolm 3) Rainwater concentrations (nmol F -1) 

8 Chester ef a/. (1993b). b Duce etal. (1976b). cArimoto ef a/. (1987). 

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Harrison, R.M. (1986) Chemical speciation and reaction pathways of metals in the atmosphere. In Toxic Metals in the Atmosphere (eds Nriagu, J.O. and Davidson, C.I.). Wiley, Chichester. 

Harrison, R. M., Chemical Speciation and Reaction Pathways of Metals in the Atmosphere, Advan. Environ. Sci. Technol. 17 [1986] 319/33. 

Understanding heterogeneous chemistry (4) the structure of natural organic matter (2) air sources and characterization of toxics (1) speciation of toxic metals (1) smokestack emissions beyond SOx and NOx (1) chemical sources of toxicity of fine particulate matter (PM2.5) (1) environmentally persistent free radicals (1) understanding of greenhouse gases in the atmosphere (carbon cycles and sinks)... 

Three atmospheric sites in the Chesapeake Bay watershed, and in close proximity to the Bay itself, were continuously monitored in 1997/98 as part of a large EPA-funded study of the atmospheric speciation of metals and organic contaminants and of the concentration of these constituents in wet and dry deposition (77, 18, 20, 21). There was an urban site, located on the roof of the Science Center (SC) in downtown Baltimore (Figure 1) and two more rural sites. These sites were the Chesapeake Biological Laboratory (CBL) at the mouth of the Patuxent River (about 60 km from the nearest city) and Stillpond (STP), on the eastern shore of the northern Chesapeake Bay and within 20 km of Baltimore (Figure 1). Previous studies occupied sites at Elms, Wye and Lewes (Figure 1) and a site in western Maryland near Frostburg (FRB). 

The humantoxic and ecotoxic effects of a metal depend strongly on its binding form [STUMM and KELLER, 1984]. Speciation of the heavy metal binding forms in the environmental compartments hydrosphere, atmosphere, and pedosphere is of considerable importance [LUND, 1990]. In most cases the individual species have to be separated before analysis [FUCHS and RAUE, 1981 FRIMMEL and SATTLER, 1982],... 

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