The Índice Metropolitano de la Calidad del Aire or IMECA, in English meaning the Metropolitan Index of Air Quality, is the reference value system for the levels of air pollution in the Mexico City Metropolitan Area, within the Valley of Mexico.
It is a real-time monitoring of the concentrations of several pollutants in the atmosphere of the Mexico City Metropolitan Area.
The IMECA is used to show the level of pollution and the level of risk that represents to the human health in the greater Mexico City and also the time of the measurements or the actions recommended for protection.
The IMECA is calculated using the measurements of average times of the chemicals ozone (O3), sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and particles lower than 10 micrometers (PM10).
To report the quality of the air, the IMECA uses 5 index categories: