Tropospheric aerosol ionic composition in the Eastern Mediterranean region

Abstract

Concentrations of the major soluble ions: sulfate (SO4=), nitrate (NO3-), chloride (Cl-), methanesulfonate (MSA), sodium (Na+), ammonium (NH4+), 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-SO4= (non-sea salt sulfate) and NH4+ and Cl- and NO3=. The NH4+/SO4= 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-SO4= concentrations suggests that H+ is probably the missing cation. Taking into consideration MSA/nss- SO4= 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.