The air quality index, ICA (from "Índice de Calidad de Aire" in spanish) is used as a reference to define the level of pollution in air. It is necessary to measure the following pollutants to get this value: carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM10), sulphur dioxide (SO2). A higher ICA means a worse air quality.

Those elements were selected to watch pollution of the atmosphere. The European Community had set the levels that can not be passed to take care of population health.