A series of 7-week sampling campaigns were conducted in urban background sites in the six European cities as follows: Duisburg 4 October–21 November 2002 (autumn), Prague 29 November 2002–16 January 2003 (winter), Amsterdam 24 January–13 March 2003 (winter), Helsinki 21 March–12 May 2003 (spring), Barcelona 28 March–19 May 2003 (spring) and Athens 2 June–21 July 2003 (summer). The campaigns were scheduled to include seasons of local public health concern due to high PM concentrations or findings in previously conducted epidemiological studies. Aerosol samples were collected in parallel with two identical virtual impactors (VI), which divide air PM into two size fractions, PM_2.5 and PM_2.5-10. The filter samples were analysed with a microbalance, an energy dispersive X-ray fluorescence (ED-XRF), an ion chromatograph (IC) and a thermo-optical carbon analyser (TOA). The PM_2.5 and PM_2.5-10 campaign means ranged 8.3–29.6 µg m^-3 and 5.4–28.7 µg m^-3, respectively. The ''wet and cool'' seasons favoured low coarse PM concentration and high fine PM concentration, whereas the spring and summer led to low fine and high coarse PM concentrations. The contribution of particulate organic matter (POM) to PM_2.5-10 was highest (27%) in Prague and the lowest (10%) in Barcelona, while those to PM_2.5 were generally higher, ranging from 21% in Barcelona to 54% in Prague. The contribution of elemental carbon (EC) to PM_2.5-10 were relatively low (1–6%) in all the six European cities but it contributed somewhat higher (5–9%) to PM_2.5. The differences are most likely due to variable contributions of local emission sources and seasonal factors such as domestic heating, vehicle exhausts and photochemical reactions. Carbonate, which interferes with carbon analysis by evolving stage at 900°C, was detected in the coarse particles of Athens and Barcelona and it could be separated reliably from OC by a simple integrating method. The calcium carbonate in Athens and Barcelona accounted for 56% and 11% of coarse PM masses, respectively. Carbonate was not found in other cities or in PM_2.5. The mean PM_2.5 mass portions of five OC thermal fractions (OC1, OC2, OC3, OC4 and OCP) varied in the range 26–33%, 6–10%, 7–10%, 9–22% and 29–50%, respectively, in six cities. The differences in the mass portion profiles were relatively small between the cities.