Sources of atmospheric methanesulphonate, non-sea-salt sulphate, 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 February 1992) at Baring Head on the southern end of New Zealand's North Island. In remote marine air, mean winter, spring and summer aerosol phase concentrations (ng m(-3)) were, respectively, non-sea-salt sulphate (NSSS) = 115, 139 and 187, methanesulphonate (MSA) = 1.5, 23 and 48, nitrate (NO3-) = 293, 70 and 84, and ammonium (NH4+) = 44, 39 and 59. Mean gas phase concentrations were sulphur dioxide (SO2) = 39, 39 and 30, nitric acid (HNO3) = 18, 30 and 27 and ammonia (NH3) = 74, 42 and 31. Although natural sources for atmospheric reactive sulphur and nitrogen predominate in this region, evidence was also found for the existence of additional, non-oceanic sources of NO3- and NSSS, including a long-range transport source of ammonium sulphate. Diurnal fluctuations were seen with lower SO2 and NH3 concentrations at night, while nighttime 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 samples, respectively. These could be only partially explained by known DMS oxidation mechanisms, and a low, relatively constant background concentration of non-DMS NSSS appeared to be present at all times. Copyright (C) 1996 Elsevier Science Ltd