The application xEco Air ("eXtreme ECOlogy" - Extreme Ecology) presents the European Air Quality Index in the Serbia, North Macedonia, Montenegro, Bosnia and Herzegovina, Croatia and Slovenia using data on concentrations of five pollutants: Suspended particles up to 10 and 2.5 microns in diameter (PM10 and PM2.5), sulfur dioxide (SO2), nitrogen dioxide (NO2) and ground-level ozone (O3). Measurements aggregated at the hourly and 24-hour level from automatic air quality monitoring networks (sourc