SOURCES OF AEROSOL NITRATE AND NON-SEA-SALT SULFATE IN THE ICELAND REGION

Daily aerosol filter samples were collected on Heimaey, Iceland (63.40 degrees N, 20.30 degrees W), beginning in July 1991. Samples were ana lyzed for NO3-, non-sea-salt (nss) SO42-, and methanesulfate (MSA). Al ong with SO2 and nss-SO42-, MSA is a product of the atmospheric oxidat ion of dimethyl sulfide (DMS) that is produced by marine organisms. Fo r much of the time, concentrations of aerosol nss-SO42- and NO3- were relatively low. Occasionally, however, concentrations increased sharpl y, by an order of magnitude or more, often for periods of several days . These concentration peaks were usually associated with the presence of a high-pressure field over western Europe; the large-scale wind fie lds associated with the high pressure subsequently transported polluta nts to the Iceland region. The 2-year mean NO3- aerosol concentration was 0.239 mu g/m(3), while that for nss-SO42- was 0.642 mu g/m(3); the median values were, respectively, 0.113 mu g/m(3) and 0.367 mu g/m(3) . Excluding the high-aerosol events (i.e. about 10% of the samples), t he NO3- average was 0.131 mu g/m(3) and that for nss SO42- was 0.385 m u g/m(3); these values are similar to those measured in the pristine S outh Pacific. Thus, although pollution events were relatively infreque nt, they had a substantial impact on atmospheric chemistry in this reg ion, in effect doubling the annual mean concentrations. There was a ve ry strong seasonal cycle in MSA concentrations, with a summer maximum of about 500 ng/m(3), which decreased to a few ng/m(3) in December. Th e seasonal cycle of MSA matches that of Phaeocystis pouchetii and Emil iania huxleyi, both of which are strong DMS producers; intense and wid espread blooms of these organisms are found around Iceland in the late spring and summer. During the summer, the nss-SO42-/MSA ratio was ver y low much of the time, suggesting the biogenic DMS was the dominant s ource of aerosol nss-SO42- in this region in this season.