Tropospheric aerosol ionic composition in the Eastern Mediterranean region

Concentrations of the major soluble ions: sulfate (SO 4 = ), nitrate (NO 3 − ), chloride (Cl − ), methanesulfonate (MSA), sodium (Na + ), ammonium (NH 4 + )), potassium (K + ), calcium (Ca ++ ) and magnesium (Mg ++ ), have been measured in 49 aerosol samples collected over a year period at a coastal site of the island of Crete in the Eastern Mediterranean. Significant correlations have been observed between nss‐SO 4 = (nonsea salt sulfate) and NH 4 + and Cl – and NO 3 – . The NH 4 + /SO 4 = equivalent ratio was 0.32. Comparison between total measured concentrations of anions and cations shows a clear deficit of cations. Correlation observed between the cation deficit and the nss‐SO 4 = concentrations suggests that H + is probably the missing cation. Taking into consideration MSA/nss‐SO 4 = ratios, the contribution of biogenic sulfur in the Eastern Mediterranean was evaluated between 0.6 and 28.3%. The variations in the ion concentrations are discussed conjointly with meteorological data and 5‐day back trajectories of air masses.