Ionic composition of rainwater and atmospheric aerosols in Sardinia, southern Mediterranean

Abstract

The ionic composition of 55 aerosol samples and 31 precipitation events collected in a coastal site in southem Sardinia (Capo Carbonara, 39~ ' 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 tazq/1 and NO3/nssSO4=0.6. Southem precipitations are influenced by Saharan dust alkaline effects, with avg. pH=6.75, nssCa=271 p.eq/t and NO3/nssSO4--0.4. Na/CI ratio in rain is similar to sea water (0.87), whilst in aerosols there is a CI loss (Na/CI=I.10), probably due to reaction with nitric acid. Total fluxes of Ca, Mg, NO 3 and SO 4 were 104, 9, 64 and 113 ~tg/cm z, and wet deposition exceeded (65-90%) dry deposition. Scavenging ratios (SR) as defined by the equation: SR=((Ci)rain/(Ci)air)*d, (d= 1200g/m 3) 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, C1=2400, Na, K, SO4= 1700, Mg=1000 and NO 3 =750. These numbers could be useful to infer total fluxes by