SOURCES OF ATMOSPHERIC METHANESULFONATE, NON-SEA-SALT SULFATE, NITRATE AND RELATED SPECIES OVER THE TEMPERATE SOUTH-PACIFIC

Aerosol species and trace gases were collected during three intensive sampling periods representing winter (2 July to 9 August 1991), spring (29 September to 6 November 1991) and summer (15 January to 29 Februa ry 1992) at Baring Head on the southern end of New Zealand's North Isl and. In remote marine air, mean winter, spring and summer aerosol phas e concentrations (ng m(-3)) were, respectively, non-sea-salt sulphate (NSSS) = 115, 139 and 187, methanesulphonate (MSA) = 1.5, 23 and 48, n itrate (NO3-) = 293, 70 and 84, and ammonium (NH4+) = 44, 39 and 59. M ean gas phase concentrations were sulphur dioxide (SO2) = 39, 39 and 3 0, nitric acid (HNO3) = 18, 30 and 27 and ammonia (NH3) = 74, 42 and 3 1. Although natural sources for atmospheric reactive sulphur and nitro gen predominate in this region, evidence was also found for the existe nce of additional, non-oceanic sources of NO3- and NSSS, including a l ong-range transport source of ammonium sulphate. Diurnal fluctuations were seen with lower SO2 and NH3 concentrations at night, while nightt ime sources of NSSS and HNO3 were indicated. Molar ratios of MSA/NSSS in remote air were 1.3, 16.3 and 25.7% for winter, spring and summer s amples, respectively. These could be only partially explained by known DMS oxidation mechanisms, and a low, relatively constant background c oncentration of non-DMS NSSS appeared to be present at all times. Copy right (C) 1996 Elsevier Science Ltd