INFLUENCE OF SEA-SALT ON AEROSOL RADIATIVE PROPERTIES IN THE SOUTHERN-OCEAN MARINE BOUNDARY-LAYER

There has been considerable debate about the relative importance of se a-salt and sulphate from non-sea-salt sources in determining aerosol r adiative effects in the marine boundary layer In the marine boundary l ayer, the most numerous aerosols are volatile sulphate particles small er than about 0.08 mu m (ref. 1) and most of the aerosol mass is in a few sea-salt particles larger than 1 mu m. Yet intermediate-size aeros ols between about 0.08 and 1 mu m diameter are the most relevant to th e radiative forcing of climate because they efficiently scatter solar radiation and also serve as cloud nuclei(2). Indeed, Charlson et al.(3 ) hypothesized that oceanic production of sulphate aerosols from the o xidation of dimethyl sulphide could be a powerful feedback in the clim ate system. It is generally assumed that marine aerosols smaller than about 1 mu m are non-sea-salt sulphate, but a recent review cites indi rect evidence that many aerosols in the sub-micrometre range contain a t least some sea-salt(4,5), Here we present direct observational evide nce from a remote Southern Ocean region that almost all aerosols large r than 0.13 mu m in the marine boundary layer contained sea-salt. Thes e sea-salt aerosols had important radiative effects: they were respons ible for the majority of aerosol-scattered light, and comprised a sign ificant fraction of the inferred cloud nuclei.