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• The finest urban air PM was distributed evenly throughout the town. • Urban air particulate matter induced DNA damage in bacteria, plant and human cells. • Mutagenicity was associated with the finest fraction of PM (PM 0.5 and PM 0.5-3). • PM 0.5 exhibited the highest concentration of PAHs and genotoxic potential. • Metals and semi-metals in PM 10 originate from traffic and steel plants. Air pollution has well-known harmful effects on human beings, causing both acute and chronic diseases. Some data suggest that genetic damage occurring early in life may influence the risk of having cancer and other chronic diseases in adulthood. Therefore, there is a growing interest in studying the genotoxic activity of air pollution, and especially particulate matter. The aim of this study was to analyze airborne particulate matter (PM 10) collected in an industrialized town of Northern Italy. PM 10 was sampled in six areas of the town, divided in three distinct dimensional classes (<0.5 μm; 0.5–3 μm and 3–10 μm), and analyzed for the quantification of polynuclear aromatic hydrocarbons and metals contents. A model-based approach using diagnostic ratios and toxic equivalency factor was also followed. Concurrently, biological assays were performed for the assessment of mutagenicity and genotoxicity in bacteria, human and plant cells. Mutagenicity was observed in bacteria and human cells, with a clear dose-response relationship, induced above all by the finest PM samples (PM 0.5 and PM 0.5-3), which contained the largest number of polycyclic aromatic hydrocarbons. DNA damage, such as chromosomal aberrations and micronuclei, was also found in Allium cepa root cells, but without a clear relationship with the tested doses. The in-vitro models utilized showed to be good indicators of air quality for mutagenicity. Chemical analyses evidenced high content of polycyclic aromatic hydrocarbons, metals and semi-metals in PM extracts. Polycyclic aromatic hydrocarbons, metals and mutagenicity can be ascribed mainly to vehicular traffic (in terms of both exhausted gases emission and mechanical losses), which represents a constant and ubiquitous source of human exposure, and to steel working, carried out within the urban area. [ABSTRACT FROM AUTHOR]