Daily mass concentrations of PM1, PM2.5, and PM10 were measured along with meteorological parameters from October 2008 to October 2009 in the city of Elche, close to the southeastern Spanish Mediterranean coast. Annual mean levels of 9.2, 13.2, and 26.2 μg m −3 were obtained for PM1, PM2.5, and PM10, respectively. PM2.5 and PM10 concentrations were lower than those previously measured at the same location due to unusual weather conditions that occurred during winter 2009, specially the decrease in the number of high atmospheric stability episodes. The contribution of road traffic to the levels of submicron (PM1), fine (PM2.5-1), and coarse (PM10-2.5) particles was studied by correlating PM concentrations with NO 2 . The results showed a higher relative contribution in winter (0.45

The performance and the uncertainty of receptor models (RMs) were assessed in intercomparison exercises\ud employing real-world and synthetic input datasets. To that end, the results obtained by different\ud practitioners using ten different RMs were compared with a reference. In order to explain the differences\ud in the performances and uncertainties of the different approaches, the apportioned mass, the number of\ud sources, the chemical profiles, the contribution-to-species and the time trends of the sources were all\ud evaluated using the methodology described in Belis et al. (2015).\ud In this study, 87% of the 344 source contribution estimates (SCEs) reported by participants in 47\ud different source apportionment model results met the 50% standard uncertainty quality objective\ud established for the performance test. In addition, 68% of the SCE uncertainties reported in the results\ud were coherent with the analytical uncertainties in the input data.\ud The most used models, EPA-PMF v.3, PMF2 and EPA-CMB 8.2, presented quite satisfactory performances\ud in the estimation of SCEs while unconstrained models, that do not account for the uncertainty in\ud the input data (e.g. APCS and FA-MLRA), showed below average performance. Sources with well-defined\ud chemical profiles and seasonal time trends, that make appreciable contributions (>10%), were those\ud better quantified by the models while those with contributions to the PM mass close to 1% represented a\ud challenge.\ud The results of the assessment indicate that RMs are capable of estimating the contribution of the major\ud pollution source categories over a given time window with a level of accuracy that is in line with the\ud needs of air quality management

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.

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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.