Air pollution caused by nitrogen dioxide mainly results from road traffic. In a statement the EC said “Portugal has recorded continuous and persistent exceedance of the yearly limit value for nitrogen dioxide in three air quality zones: North Lisbon, Coastal Porto, and between the Douro and Minho”.

Pollution caused the early deaths of 4,900 people in Portugal in 2019. The European Environment Agency (EEA) estimates that in 2019, air pollution caused the premature death of 364,200 people across the European Union, despite indicating that over recent years early deaths due to air pollution have been dropping.