Abstract. We collected weekly aerosol samples using high-volume impactors over a period of 20 months (1988)(1989)(1990) at the Cape Grim baseline station on the northwestern coast of Tasmania, Australia. The samples were analyzed for soluble ionic constituents, including sulfate, methanesulfonate (MS-), ammonium, nitrate, and the major sea-salt ions. The sea-salt component showed only a slight seasonal variation, whereas the non-sea-salt (nss) ions all had pronounced summer maxima. Significant interannual variability was seen between the nss ion concentrations measured during the two summers investigated. Nss sulfate and MSwere present both in the fine and coarse aerosol fractions, in the latter presumably associated with sea-salt particles. During the winter period, there was more nss sulfate in the coarse fraction than in the fine fraction. These observations are consistent with an important role of liquid-phase oxidation in haze and cloud droplets for the production of nss sulfate aerosol.

Speciation studies are necessary to understand the biogeochemical cycling of arsenic in aquatic systems. The species of arsenic present, their behaviour and toxicity will change depending on the biotic and abiotic conditions in the water. In groundwater, arsenic is predominantly present as arsenite (As III ) and arsenate (As V ). The major arsenic species in freshwater are As III and As V and minor amounts of MMA , DMA and methylated As III have also be detected. In seawater, the arsenic speciation differs in the surface and deep zone. In addition to the above species, uncharacterized arsenic species may constitute a significant portion of the total arsenic present in some water and the identification of these compounds is necessary to fully understand the arsenic biogeochemistry in water.A knowledge of the speciation of As in natural water is important because the bioavailability and the physiological and toxicologial effects of As depend on its chemical forms. Arsenic occurs in a variety of chemical forms in water, and this is a result of many chemical and biological transformations in the aquatic environment. The mechanism of transport and biological availability of arsenic depends on the chemical species present.The main arsenic compounds detected in natural waters are arsenite [As 111 ],

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