were used. To evaluate the exposures both short-term (hourly and daily) data and long term (yearly) data during 45 years were analysed. For health risk assessment the relationship between exposure and biological effects of pollutants published by the WHO and the US EPA were employed. Results: During the studied period annual average concentrations of PM 10 ranged from 25 to 96 µg/m 3 ; PM 2.5 from 24 to 45 µg/m 3 ; SO 2 from 3.4 to 101.5 µg/m 3 ; NO 2 from 17.76 to 51.17 µg/m 3 ; benzene from

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... 24 to 9.2 µg/m 3 ; benzo[a]pyrene from 2.1 to 14 ng/m 3 ; arsenic from 1.2 to 9.5 ng/m 3 . Since the turn of the 80s and 90s of the 20th century trend of air pollutant concentrations has been decreasing until the turn of millennium, when it stopped, and it has been constant until present time. However, presented results demonstrate that the citizens of Ostrava have been exposed to relatively high concentrations of pollutants in comparison to other similar cities. The most significant pollutants contributing to health risks are airborne dust (PM 10 , PM 2.5 ), benzene and benzo[a]pyrene. The long-term average health risk of PM 10 has increased in case of postneonatal infant mortality up to 30%; prevalence of bronchitis in children up to 61%; and incidence of chronic bronchitis in adults up to 89%. The long-term average health risk of PM 2.5 increased for all-cause mortality in persons aged 30+ years up to 22%; cardiopulmonary related mortality up to 25%; and lung cancer related mortality up to 39%. The highest carcinogenic risk is observed in benzo[a]pyrene, when the range of individual lifetime carcinogenic risk is up to 1.25*10 −3 . This assessment is valid according to the strict carcinogenic risk by the WHO, while the maximum carcinogenic risk according the US EPA is 7.2*10 −5 . Conclusions: A significant reduction of the pollutants' concentrations in Ostrava in the nineties of the last century does not mean a required improvement of outdoor air quality to the desired level. Persisting episodes with a very strong short-term increase of the concentration of PM 10 and PM 2.5 , as well as long-term load of these substances on the population is very high. Health risks from such burdens are likely to lead to a higher mortality and morbidity especially from specific diseases.