a b s t r a c tParticle composition data for PM 10 samples collected at an urban background location in Elche in southeastern Spain from December 2004 to November 2005 were analysed to provide source identification and apportionment. A total of 120 samples were collected and analysed by Particle Induced X-ray Emission (PIXE) and ion chromatography. Positive matrix factorization (PMF) was used to estimate sources profiles and their mass contributions. The PMF modelling identified six sources: PM 10 mass was apportioned to secondary nitrate (26%), secondary sulphate (22%), local soil dust (21%), traffic (13%), seasalt (11%) and African dust (7%). It is worth noting that PMF was able to identify a Saharan dust source even in the presence of a weighty local dust source, and to quantitatively estimate the contributions of these two sources. The African dust contribution varies, depending on the intrusion days, within a range of 5-40% of the total PM 10 concentration. Without the contribution of Saharan dust, 50% of the total exceedances of the PM 10 50 mg m À3 EC limit during the studied period would not have taken place.

PM2.5 and PM10 samples were collected in the urban atmosphere of Elche (southeastern Spain) between December 2004 and November 2005. The samples were analyzed for mass and water-soluble inorganic ions (Na + , NH þ 4 , K + , Ca 2+ , Mg 2+ , Cl − , NO À 3 and SO 2À 4 ) with the aim of investigating the influence of the climatic and geographic features of a coastal semiarid area on the contribution of these species to PM levels. Secondary inorganic ions (SO 2À 4 , NO À 3 , NH þ 4 ) were the major components in the fine fraction (PM2.5), accounting for 40% of the total mass. The relationship between non-marine SO 2À 4 and NH þ 4 indicated that fine sulfate particles were completely neutralized by ammonium. In the coarse fraction (PM10-2.5), nitrate (as NaNO 3 and Ca(NO 3 ) 2 ), together with crustal (CaCO 3 ) and marine species (NaCl) accounted for almost 50% of the total mass. Fine sulfate and coarse nitrate showed summer maximums. In contrast, the concentrations of fine NO À 3 were lowest in the warm period. Ammonium presented both winter and summer maximums. The levels of marine ions, except for coarse Cl − , were highest in summer when the dominant wind flow is from the sea. No significant seasonal variations were observed for coarse Ca 2+ and SO 2À 4 . The concentrations of all inorganic ions increased during Saharan dust events, in particular, fine NH þ 4 and SO 2À 4 and coarse NO À 3 . Coarse calcium was proved not to be a good tracer for this type of episode in our region since the average levels of this cation are elevated and the relative increase in its concentrations during African events was not as high as expected.

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