Recent trends in nitrogen dioxide (NO2) levels in air (Ireland)

Date released: May 26 2020

The dominant source of the pollutant nitrogen dioxide in our air is traffic. The EPA has carried out an analysis of ambient nitrogen dioxide at its national monitoring stations over recent weeks:

  1. between January, February, March and April of this year
  2. between the same time period this year and last

There is clear evidence that there has been a decrease in air pollution particularly towards the end of March and beginning of April coinciding with the introduction of the restrictions on movement relating to Covid-19. The most significant changes were in the concentrations of NO2 with decreases of up to 50%, as compared to the January average (mean) value. The largest decreases were observed at urban traffic stations in the National Air Quality Monitoring Network.

Statistical analysis

The data reviewed were from 12th March onwards.  This is the date when schools closed, and commuter traffic levels were expected to have started to decrease.

Concentrations of air pollution are highly variable and can change quite substantially from day to day because of the variations in emissions (for example the impacts of commuter traffic, weekdays and weekend days) as well as changes in the weather conditions. This means that it is necessary to assess data for a substantial period-of-time. International guidance recommends using data averaged over a period of about a month to be able to accurately assess if there is a real change from typical levels.

We are currently analysing nitrogen dioxide concentrations from multiple previous years and performing more detailed evaluations of the actual decrease from the mean (average) monthly values. Once complete this will be provided on


  • All of our hourly air quality data is on our website
  • Nitrogen dioxide is a pollutant that is emitted in ambient air when petrol or diesel is burned in internal combustion engines
  • Day to day variations in air pollution levels due to meteorological conditions can typically be up to 25% - 30%.
  • The European Environment Agency has developed a viewer that tracks the weekly average concentrations of nitrogen dioxide and particulate matter for member states. Users can select different pollutants, countries and cities. The viewer shows weekly averages for each city.
  • The National Ambient Air Quality Network includes roadside stations (“traffic stations”) as well as “background stations” that may be located in urban, suburban or rural areas.

With regard to Air Quality Policy, which is led by the Department of Communications and Climate Action, the EPA also notes:

  • In relation to improving air quality in Ireland, work is continuing on the National Clean Air Strategy, which will be the first all of government response reducing air pollution and promoting cleaner air. Emissions from the transport sector, including idling, will be considered in the context of the Strategy. Restrictions on car idling, including outside of schools, will be considered as part of this strategy.
  • In tandem with this, the Climate Action Plan includes a number of actions which will also have a significant impact on reducing emissions and improving air quality, including:
    • Putting 180,000 electric vehicles on our roads by 2025 and almost 1m by 2030
    • Ensuring the EV charging network underpins public confidence
    • Decarbonising the public transport fleet
    • Develop a 5 year cycling strategy and roll out 200km of new cycle lanes through bus connects
    • Developing a new Park and Ride Strategy, to reduce congestion and lower journey times
    • Developing a regulatory framework on low emission zones and parking pricing policies, and provide local authorities with the power to restrict access to certain parts of a city or a town to zero emission vehicles only
    • Legislating for no new fossil fuel vehicles to be sold from 2030 onwards.