To improve the regional system for assessment and management of the ambient air quality in the North-East Estonian region of oil shale mining and processing, as well as natural areas, the corresponding Air Quality Complex Index (AQI) has been elaborated. This method enables to generalize a large number of measured numerical values of concentrations of pollutants in case of multicomponential pollution fields and makes the results more easily understandable. The AQI is suitable for the real-time monitoring as well as for prediction of air quality values and pollution situations by calculated data.