Quantification of Saharan and local dust impact in an arid Mediterranean area by the positive matrix factorization (PMF) technique

Particle 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%), sea-salt (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 mu g m(-3) EC limit during the studied period would not have taken place.