Daily bulk aerosol filter samples were collected at Erdemli (36.6degreesN, 34.3degreesE) on the Mediterranean coast of Turkey for a 4-year period between 1996 and 1999. Concentrations of the water-soluble ions (Cl-, Br-, NO3-, SO42-, C2O42- MSA(-), Na+; NH4+, K+, Mg2+ and Ca2+) were measured in a total of 610 samples. In addition, three-dimensional (3-D), 3-day back trajectories of air masses arriving daily at Erdemli were calculated to determine potential aerosol source regions. The results indicated that the seasonal variability of atmospheric concentrations for ionic species at Erdemli were related to precipitation events. The atmospheric concentration of measured species (except those of a marine origin) decreased to minimum values during winter, whereas, during dry summer months the lack of precipitation resulted in their accumulation in the atmosphere. During the transition periods, although there was still precipitation, crustal ions (mainly nss-Ca2+ and in lesser extent nss-K+ and nss-Mg2+) exhibited sporadic but intense concentration peaks due to the intrusion of dust from the Sahara and the Arabian Peninsula. The results obtained from factor analysis and inter-species correlation suggested the presence of three main sources influencing concentrations: crustal, marine and anthropogenic sources. Multiple regression analysis indicated that the main non-sea-salt ions were associated with the formation of NH4HSO4, (NH4)(2)SO4, Ca(NO3)(2), CaSO4 and CaCO3. Formation of NH4NO3 and partial neutralization of H2SO4 by NH4+ and Ca2+ was found to occur mainly in summer. (C) 2004 Elsevier Ltd. All rights reserved.