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Ionic composition of rainwater and atmospheric aerosols in Sardinia,southern Mediterranean |
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| Authors: | S Guerzoni A Cristini R Caboi O Le Bolloch I Marras L Rundeddu |
| Institution: | 1. Ist. Geologia Marina/CNR, via Gobetti 101, 40129, Bologna, Italy 2. Dip. Sc. della Terra/Università, via Trentino 51, 09126, Cagliari, Italy 3. International Marine Centre, Torregrande (OR), Italy |
| Abstract: | The ionic composition of 55 aerosol samples and 31 precipitation events collected in a coastal site in southern Sardinia (Capo Carbonara, 39°06 N; 09°31 E) were compared. The samples were collected during one year period (Oct'90/Oct'91) and showed high variability in composition according to meteorological conditions. Rain and soluble part of aerosol showed a strikingly similar ionic composition: most significant anions were chlorine and sulphate, and sodium is the principal cations, followed by magnesium and calcium. The acid events are associated with N-NW trajectories (anthropogenic influxes from N. Europe) with avg. pH=4.65, non sea salt (nss) Ca=60  eq/l and NO3/nssSO4=0.6. Southern precipitations are influenced by Saharan dust alkaline effects, with avg. pH=6.75,nssCa=271 eq/l and NO3/nssSO4=0.4. Na/Cl ratio in rain is similar to sea water (0.87), whilst in aerosols there is a Cl loss (Na/Cl=1.10), probably due to reaction with nitric acid. Total fluxes of Ca, Mg, NO3 and SO4 were 104, 9, 64 and 113 g/cm2, and wet deposition exceeded (65–90%) dry deposition. Scavenging ratios (SR) as defined by the equation:SR=(Ci)rain/(Ci)air]
*d, (d=1200g/m3) were calculated, using geometric means (Ci) of precipitation and aerosols collected concurrently during the period (a total of 23 samples). The SR values are Ca=3400, Cl=2400, Na, K, SO4=1700, Mg=1000 and NO3=750. These numbers could be useful to infer total fluxes by using simply rainwater ionic composition in Mediterranean semi-arid sites like Sardinia. |
| Keywords: | ionic fluxes acidic deposition Saharan influence particulate fluxes scavenging ratio |
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