In southern European cities, accumulation and resuspension of road dust are favored by the scarce rainfall as compared to central and northern countries. Indeed, a comparison of several European studies shows that PM in Mediterranean countries is considerably enriched in mineral dust: soil fraction accounts for 22% in Amsterdam whilst 65% in Athens (Sillanpa¨a¨ et al., 2006), mineral dust achieves 10 mg m3 in Spain while 2–5 in central Europe and 7–9 in Sweden (Querol et al., 2004). Viana et al. (2007) registered 23–33% of mineral matter in PM10 in Barcelona (Spain),
while only 9% in Ghent (Belgium). Moreover, even in areas with high background mineral load, Querol et al. (2004) found that the highest mineral dust concentrations were recorded at urban background sites rather than at rural or suburban background sites.