Non-sea-salt sulfate, methanesulfonate, and nitrate aerosol concentrationsand size distributions at Cape Grim, Tasmania

We collected weekly aerosol samples using high-volume impactors over a peri od of 20 months (1988-1990) at the Cape Grim baseline station on the northw estern coast of Tasmania, Australia. The samples were analyzed for soluble ionic constituents, including sulfate, methanesulfonate (MS-), ammonium, ni trate, and the major sea-salt ions. The sea-salt component showed only a sl ight seasonal variation, whereas the non-sea-salt (nss) ions all had pronou nced summer maxima. Significant interannual variability was seen between th e nss ion concentrations measured during the two summers investigated. Nss sulfate and MS- were present both in the fine and coarse aerosol fractions, in the latter presumably associated with sea-salt particles. During the wi nter 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. The seasonal behavior of the sulfur and nitrogen species at Cape Grim and their mutual correlations suggest that DMS oxidation is th e dominant sulfur source during summer, while nonbiogenic sulfur sources ma ke significant contributions to nss sulfate outside of this season. Correla tions of CN and CCN concentrations with nss sulfate, MS-, and wind speed su ggest that DMS oxidation and, to a lesser extent, seaspray formation contri butes to CN and CCN populations. The contrast between the weak seasonality of the sea-salt component and the pronounced seasonal behavior in both sulf ur species and CCN supports the central role of biogenic DMS emissions as p recursors of CCN in this region, at least in the biologically productive se ason.