Exposure to particulate matter (PM) in ambient air has been shown to lead to adverse health consequences. Six size fractions of PM with aerodynamic diameter smaller than 10 μm (PM 10) and gas phase were collected at six localities with different major pollution sources. Extracts of samples were assessed for AhR-mediated toxicity, (anti-)estrogenicity, (anti-)androgenicity and genotoxicity. The biological responses were interpreted relative to chemical characterization. Historically, for regulatory purposes, evaluation of air pollution was based mainly on assessment of the sum of PM 10 . In the case of AhR-mediated activity, PM 1 was responsible for more than 75% of the activity of the particulate fraction from all localities. The assessed effects were correlated with concen-trations of polycyclic aromatic hydrocarbons (PAH), organic carbon content and specific surface area of the PM. A significant proportion of biologically active chemicals seems to be present in the gas phase of air. The results sug-gest that an average daily exposure based just on the concentrations of contaminants contained in PM 10 , as reg-ulated in EU legislation so far, is not a sufficient indicator of contaminants in air particulates and adoption of standards more similar to other countries and inclusion of other parameters besides mass should be considered.