Individual aerosol particles collected in the Negev desert in Israel during a summer and winter campaign in 1996-1997 were analysed by scanning electron microscopy and transmission electron microscopy with energy-dispersive X-ray analysis. Hierarchical cluster analysis was performed to interpret the data on the basis of particle diameter and composition. Eleven particle classes (groups) provided clues on sources and/or particle formation. The summer samples were enriched in sulphates and mineral dusts; the winter samples contained more sea salts, aged sea salts and industrial particles. Mineral dust and sea-salt particles became more abundant with increasing particle size, while sulphates and other sulphur containing particles increased with decreasing particle size. The fine size fraction below 1 m diameter was enriched in secondary particles and showed evidence of atmospheric processing. The secondary sulphate particles were mainly attributed to long-range transport. A regional conversion from calcite to sulphate occurred during summer. Industrial particles originating from local pollution appeared during winter.