The air quality index (AQI) is a generic indicator for reporting air quality and its effects on health in a given location. It indicates the existing level of contamination at a location, its potential health effects and the recommendations that must be followed to protect air quality.

At Eltiempo.es we follow the method used by the EPA (American Environmental Protection Agency) to calculate the air quality index. By applying its formulas, we can calculate the air quality index for each pollutant, depending on its concentration. When we have calculated the indices for each pollutant, we select the one with the most unfavorable value. That value is then considered to be the air quality index for that moment.