According to a report from the European Environment Agency, from 2014 to 2020, almost two thirds of all cases in which air quality thresholds were exceeded were linked to heavy traffic in cities and the proximity of main roads and were linked to nitrogen oxide.

Six countries, including Portugal, reported road traffic as the only source of limit violations. The other countries mentioned were Austria, Denmark, Finland, the Netherlands and the United Kingdom (which was still part of the European Union).

In addition to road traffic, the other source that gave rise to infringements was domestic heating, in this case essentially emission of particles and in countries such as Croatia, Italy, Poland and Slovenia, among others.

The data released refer to the evaluation by the European Environment Agency (EEA) of air quality plans for countries.

According to the EEA report "Air Quality in Europe 2021", exposure to air pollution caused a significant amount of premature deaths and illness in the 27 EU Member States in 2019, with 307,000 premature deaths attributed to fine particles and 40,400 to nitrogen dioxide.

The European Commission has set a target of reducing premature deaths caused by fine particulates by 55% by 2030, compared to 2005 levels. The Commission is also reviewing the air quality guidelines to bring them in line with the Organization's new guidelines.