Aerosol fine fraction in the Venice Lagoon: Particle composition and sources

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 (SO42−), 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-SO42−) 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 (R2 = 0.93), suggesting that a common source makes a high contribution to the measured concentrations.