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Average ranges of particulate matter (PM10 and PM2.5) concentrations and chemical composition in Spain show significant variations across the country, with current PM10 levels at several industrial and traffic hotspots exceeding recommended pollution limits. Such variations and exceedances are linked to patterns of anthropogenic and natural PM emissions, climate, and reactivity/stability of particulate species. PM10 and PM2.5 concentrations reach 14-22 mu g PM10 m(-3) and 8-12 mu g PM2.5 m(-3) at most rural/regional background sites, 25-30 mu g PM 10 m(-3) and 15-20 mu g PM2.5 m(-3) at suburban sites, 30-46 mu g PM10 m(-3) and 20-30 mu g PM2.5 m(-3) at urban background and industrial sites, and 46-50 mu g PM10 m(-3) and 30-35 mu g PM2.5 m(-3) at heavy traffic hotpots. Spatial distributions show sulphate and carbon particle levels reach maxima in industrialised areas and large cities (where traffic emissions are higher), and nitrate levels increase from the Atlantic to the Mediterranean (independent of the regional NO, emissions). African dust outbreaks have an influence on the number of exceedances of the daily limit value, but its additional load on the mean annual PM10 levels is only highly significant in Southern Iberia and Canary and Balearic islands. The marine aerosol contribution is near one order of magnitude higher in the Canaries compared to the other regions. Important temporal influences include PM intrusion events from Africa (more abundant in February-March and spring-summer), regional-scale pollution episodes, and weekday versus weekend activity. Higher summer insolation enhances (NH4)(2)SO4 but depletes particulate NO3- (as a consequence of the thermal instability of ammonium nitrate in summer) and Cl- (due to HCl volatilisation resulting from the interaction of gaseous HNO3 with the marine NaCl), as well as generally increasing dry dust resuspension under a semi-arid climate. Average trace metal concentrations rise with the highest levels at industrial and traffic hotspots sites, in some cases (Ti, Cr, Mn, Cu, Zn, As, Sn, W, and Pb) exceeding rural background levels by over an order of magnitude. (C) 2006 Elsevier Ltd. All rights reserved.