Nitrogen Dioxide Air Pollution

The "Nitrogen Dioxide Air Pollution" fact sheet analyses the progress towards the objectives imposed for this pollutant across the country, in order to safeguard the protection of human health.

Nitrogen dioxide (NO2) is mainly produced by industrial and automotive combustion and the oxidation of nitrogen fertilizers, with potential health effects, which can result in increased susceptibility to respiratory diseases, especially in children, and in lung function, especially in asthmatics.

The determination of the NO2 annual average, resulting from the concentrations recorded in the monitoring stations in each zone, allows the respective comparison with the limit value (LV) stipulated in the legislation for the protection of human health.

The measured NO2 levels differ according to the type of station, whether by the surroundings (rural, suburban or urban) or by the influence of the pollution source (traffic, industrial or background). The analysis of the aggregated hourly average values according to this typology, allows the identification of the evolution trend according to the nature of the emission source, enabling a more optimized targeting of action for its reduction.

For this assessment, all stations with a measuring efficiency greater than 75% are used. For stations covered by the indicative measurement assessment strategy, measurements with an efficiency greater than 14% are also used.

This fact sheet concerns mainland Portugal, the Autonomous Regions of Madeira and the Azores and will be updated annually.


Objectives and targets: 
  • Ensure compliance with the EU-wide targets for ambient air quality, which aim to avoid, prevent or limit the harmful effects of air pollutants on human health and the environment;
  • Measure ambient air quality across the country, with a special focus on urban centres;
  • Preserve air quality where it is good and improve it in other cases;
  • As targets, the limit values set forth in the legislation are not to be exceeded  (Decree-Law no. 102/2010):
    • limit value for the average hourly concentration of 200 μg/m3 of NO2, not to be exceeded more than 18 times per calendar year;
    • Limit value for the average annual NO2 concentration of 40 μg/m3.
Progress analysis:
Last update: 
Monday, 29 October, 2018