Ozone, sulphur dioxide, condensation nuclei and aerosol composition over the eastern part of the North Atlantic basin

Surface concentrations of ozone, sulphur dioxide, condensation nuclei (CN) and aerosol composition were investigated during the international marine expedition to the eastern part of the North Atlantic and Mediterranean sea (27 March–17 June 1991). Space-temporal distribution of the concentrations is discussed in connection with transport of polluted air from European continental sources to the oceanic atmosphere. Corresponding episodes were identified using back trajectories of the air parcels and 222Rn as a tracer of continental air. CN concentrations increased considerably during the periods of atmospheric transport from industrial regions, being the most sensitive indicator of anthropogenic pollution. The same is typical for excess sulfate while for SO2 an anthropogenic input is relatively small. Particulate matter of polluted air is presented mainly by excess sulfate and ammonium ion with 30–40% lack of chlorine as compared with the sea salt composition. Ozone concentrations up to 76.2 ppbv were registered over the Mediterranean sea in the air masses transported from Northern Italy and Southern France while the background level of O3 for the North Atlantic is estimated by the value 27 ppbv with standard deviation of 2 ppbv. The contribution of anthropogenic ozone into its concentration measured in the remote North Atlantic atmosphere was from 14 to 26 ppbv with maximum reaching 42 ppbv. Rapid variations and high correlation between O3, CN and 222Rn values were observed in the vicinity of atmospheric fronts.