Air is a mixture of various types of gases in a constant and variable ratio. The constant air components are: nitrogen (N2), oxygen (O2), hydrogen (H2) and noble gases, and the variable components are CO2 and H2O. How much air is needed for humans, it is best to say that one can live without food for about 40 days, without water for 5 days and without air for only 5 minutes. From the above data, it can be concluded that the whole human being, all its vital organs, depends directly or indirectly on air quality. Urbanization and industrialization have made significant changes in the composition of the air. Air in Croatia is mostly clean or slightly polluted, and in some urban and industrial areas it is moderately or excessively polluted. Slavonski Brod is, due to the refinery in the neighboring Bosanski Brod, which operates beyond all environmental standards, a city whose air is one of the most polluted in Europe. According to the original data from the state network for the continuous monitoring of air quality in Slavonski Brod it is concluded that air is in the second category for PM10, PM2.5 and H2S, which means that air is polluted. Air quality categories are defined for each pollutant substance specifically and refers to the protection of human health, the quality of life, the protection of vegetation and the ecosystem. This is why refinery needs to be reconstructed, and the exhaust valves should be installed with cleaners to prevent further air pollution in Slavonski Brod and its surroundings. This problem should be taken very seriously because every day there is a growing number of people suffering from various illnesses related to air pollution