Purpose: The concentrations of PM10 mass, PM2.5 mass and particle number were continuously measured for 18 months in urban background locations across Europe to determine the spatial and temporal variability of particulate matter. Methods: Daily PM10 and PM2.5 samples were continuously collected from October 2002 to April 2004 in background areas in Helsinki, Athens, Amsterdam and Birmingham. Particle mass was determined using analytical microbalances with precision of 1 μg. Pre- and post-reflectance measurements were taken using smoke-stain reflectometers. One-minute measurements of particle number were obtained using condensation particle counters. Results: The 18-month mean PM10 and PM2.5 mass concentrations ranged from 15.4 μg/m3 in Helsinki to 56.7 μg/m3 in Athens and from 9.0 μg/m3 in Helsinki to 25.0 μg/m3 in Athens, respectively. Particle number concentrations ranged from 10,091 part/cm3 in Helsinki to 24,180 part/cm3 in Athens with highest levels being measured in winter. Fine particles accounted for more than 60% of PM10 with the exception of Athens where PM2.5 comprised 43% of PM10. Higher PM mass and number concentrations were measured in winter as compared to summer in all urban areas at a significance level p < 0.05. Conclusions: Significant quantitative and qualitative differences for particle mass across the four urban areas in Europe were observed. These were due to strong local and regional characteristics of particulate pollution sources which contribute to the heterogeneity of health responses. In addition, these findings also bear on the ability of different countries to comply with existing directives and the effectiveness of mitigation policies. © 2011 Springer-Verlag.