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Abstract: The work presents a characterisation of aerosol sampled during three campaigns conducted in the Venice Lagoon from 30 June to 21 July 2004, from 15 February to 10 March 2005 and from 8 May to 25 May 2006. The results yield information about the physical–chemical characteristics of fine aerosol, the possible sources and its fate. Sulphate (SO4 2−), nitrate (NO3 −) and ammonium (NH4 +) are identified as the main water soluble components. The sum of these ions in the spring campaign 2006 varies from 51% to nearly 100% of PM2.5 fraction aerosol. NH4 + is found to be significantly correlated to non-sea-salt sulphate (nss-SO4 2−) and NO3 −, thus indicating the prevalent presence of ammonium nitrate and sulphate. The overall lack of a clear diurnal and seasonal cycle of sulphate suggests a transport from the Po Valley, while the diurnal and seasonal profile of nitrate concentrations suggests a prevalence of local generation. Sulphates from sea water through oxidation of dimethylsulfide (DMS) are not negligible (about 10% of the anthropogenic sulphate). The marine aerosol contribution to PM1 and PM2.5 fractions, calculated using Na+ as a tracer of sea-salts, is low (range 1–6%). In some cases chlorine depletion is observed. The content of chlorine in the aerosol particle is mostly higher than expected for marine environments (considered on the basis of Cl−/Na+ ratio). Therefore, specific sources for the element have been suggested. Oxalic acid anion, which accounts for 55% of the organic compounds examined, presents mean values 180 ng m−3 and 161 ng m−3 in the winter and spring campaigns, comparable with reported values in low polluted urban areas. In the winter campaign there is a high correlation between formate and acetate (R 2 =0.93), suggesting that a common source makes a high contribution to the measured concentrations. [Copyright &y& Elsevier]

Abstract: The work presents the results of an experimental campaign performed at a rural site (S. Pietro Capofiume, near Bologna July 2007) concerning measurements of ice nuclei in different size classes of aerosol: PM1, PM2.5, PM10 and total suspended particles (TSP). Simultaneous measurements of particle number concentrations were also performed. Aerosol in the PM1 fraction contributes about 50% of the measured ice nuclei number concentration, and in the PM10 fraction contributes about 70–90%. Consequently, the dominant fraction of aerosol that can be activated as ice nuclei involves particles with aerodynamic diameter less than 10 μm. A positive correlation is observed between higher supersaturation with respect to ice and water (S ice and S w, respectively) values, and ice nuclei number concentration. The variations of S w from 2 to 10% and S ice from 20 to 32% (T air =−15 °C) determine an approximately threefold increase (from 110 to 337 m−3) in the ice nuclei average number concentration. There is no correlation between ice nuclei measured in the different size ranges, either with the particle number concentration measured with the counter spectrometer (d >0.3 μm) or with the condensation nuclei counter. [Copyright &y& Elsevier]