PM characteristics of seven selected regions within the European Union (EU) were analysed and compared. Results of levels and speciation studies of PM10 and PM2.5 (with at least one year of data coverage from 1998 to 2002) at regional, urban background and kerbside sites were assessed. Based on the examples selected, PM10 levels (annual mean) ranged from 19 to 24 mug m(-3) at regional background sites, from 28 to 42 mug m(-3) at urban background, and from 37 to 53 mug m(-3) at kerbside sites. PM2.5 levels varied from 8 to 20 mug m(-3) at regional background sites, 20 to 30 mug m(-3) at urban background and 25 to 40 mug m(-3) at kerbside sites. The ratio PM2.5/PM10 is highly dependent on the type of site and varied widely between different EU regions. Source apportionment results showed that, on an annual average, the natural contribution (mineral and marine) at EU regional sites was in the range of 4-8 mug m(-3) in PM10 decreasing in PM2.5, but contributions up to 19 mug m(-3) were reported for specific locations. At urban sites, carbonaceous aerosols and secondary inorganic compounds accounted for a major fraction of PM10, and especially of the PM2.5 mass. Quantitative data on the contributions of the regional background, city background and local traffic to the mean annual levels of PM10, PM2.5 and major components were supplied. Climatic differences, long-range transport processes and winter traffic peculiarities (the latter in northern countries) contributed to the increase of PM10 and PM2.5 masses. At kerbside sites, an important dust contribution to PM2.5 is highlighted. (C) 2004 Elsevier Ltd. All rights reserved.