Air Quality Index (AQI)

The “Air Quality Index” is an indicator that expresses the state of the ambient air quality at the national level and allows, through classification according to a colour scale, according to its results, to guide the citizen in order to adapt behaviours and actions towards the protection of human health, especially the most sensitive groups of the population.

The air quality index is calculated and made available on a daily basis through the QualAr information system managed by the Portuguese Environment Agency (APA), with the information made available by the Regional Coordination and Development Commissions (CCDRs) in the mainland, and Regional Directorates for the Environment (DRAs) in the autonomous regions of the Azores and Madeira.

This qualitative indicator results from the calculation of the arithmetical averages of the pollutants nitrogen dioxide (NO2), ozone (O3) and PM10 particles (particles with a diameter of 10 μm or less) and, if available, CO and SO2 pollutants are also taken into account. Their results are compared to a colour scale from "Good" to "Poor", with the worst result being the index colour. In this way, the population can adjust their behaviours according to the observed index, allowing them to protect themselves from the health effects that result from exposure to polluted air.

This fact sheet concerns mainland Portugal and the Autonomous Regions of the Azores and Madeira and will be updated on an annual basis.


Objectives and targets: 
  • Ensure compliance with the established European and domestic ambient air quality objectives which aim to avoid, prevent or limit the harmful effects of different air pollutants on human health and the environment;
  • Assess ambient air quality across the country;
  • Increase the number of days that the air quality index is rated "Good" or "Fair" and decrease the number of days it is rated "Moderate", "Poor", or "Very Poor";
  • Promote and improve public access to information on the air quality conditions and its health consequences.
Progress analysis:
Last update: 
Thursday, 23 May, 2019