Abstract In order to be able to detect annual and diurnal variation the nucleation, Aitken and accumulation mode aerosol number concentrations were investigated. In this study particulate matter and aerosol number concentrations based on three years (1999–2001) measurements in four different places, Helsinki, Hyytiälä, Pallas and Värriö in Finland were utilized. Mean PM 10 concentration was found to be in urban, urban background, disturbed rural and rural conditions 18.7, 15.3, 10.2 and 6.9 μg m −3 . PM 2.5 concentrations in urban, urban background and rural conditions were 9.6, 8.2 and 5.8 μg m −3 . PM 1 concentration in rural area were 4.1 μg m −3 . Total number concentrations between 10 and 500 nm in urban, rural and arctic background were 16660, 2110 and about 920 cm −3 , respectively. Annual cycle of different particle sizes was also investigated. Particle mass was found to have maximum during the spring and autumn. Nucleation mode particle concentrations had their maximum both in urban and rural conditions in spring and autumn. For Aitken mode a similar variation was found. Accumulation mode particles were found to have the highest concentrations during summer and the lowest concentrations during winter. In urban conditions local sources drive over natural variability, but a natural cycle can still be seen. Diurnal variation was found to be associated with traffic in urban conditions. In rural conditions, diurnal variation of nucleation mode particles were connected to new particle formation. It was also found, that there is no correlation between ultrafine (<90 nm) and larger (>90 nm) particles.