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

Date released: Jul 10 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, April, May and June of this year
  2. between the same time period this year and previous four years (where available)

There is clear evidence that there was 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, especially during the period of ‘full lockdown’. The most significant changes were in the concentrations of NO2 with decreases of up to 50%, compared with previous years. The largest decreases were observed at urban traffic monitoring stations in the National Air Quality Monitoring Network.

Further analysis

Concentrations were observed to decrease from the 12th of March when schools were closed, however it was with the introduction of ‘full lockdown’ that dramatic decreases were observed. Please see Figure 1 and Figure 2 which shows the average NO2 concentrations for the suburban traffic site of Blanchardstown for the weeks 12 and 14 for the years 2016 – 2020. Week 12 being one week before ‘lockdown’ was imposed and week 14 being two weeks after full ‘lockdown’ was imposed. These weeks were chosen as representative for their consistency of meteorological conditions between the years (similar average windspeed and similar wind direction). The graphs also show the average weekly concentration for those particular weeks across the years and also the average weekly concentration for all weeks for those years. The decrease in concentration between weeks 12 and 14 for the year 2020 can thus be attributed to the imposition of restrictions.

Figure 3 and Figure 4 show the average NO2 concentrations for the same weeks (12 and 14) at the Dublin urban traffic site of St. John’s Road West. Again, this shows the impact of the introduction of restrictions levels of NO2. Figure 5 and Figure 6 shows the same difference at the suburban traffic site at South Link Road in Cork, showing similar reductions in traffic pollution.

Figure 7 shows average NO2 concentrations by week for 2020 (year to date) for the Dublin urban traffic sites at Pearse St. and St. John’s Road West with a timeline of introduction of restrictions and subsequent easing of restrictions. This graph shows the fall in traffic pollution along with an emerging trend of increasing levels following easing of restrictions. We will continue to monitor NO2 concentrations over the coming weeks to confirm this emerging trend.

 Fig 1 Air Quality

Figure 1 Average NO2 concentrations for Blanchardstown week 12 (one week before full lockdown) 2020 and previous years 2016 - 2019

 

 Fig 2 NOx air quality

Figure 2 Average NO2 concentrations for Blanchardstown week 14 (second week of full lockdown) 2020 and previous years 2016 - 2019

 Fig 3 NOx Air Quality

 

Figure 3 Average NO2 concentrations for St. John's Road West week 12 (one week before full lockdown) 2020 and previous years 2019

 Fig 4 NOx air quality

 

Figure 4 Average NO2 concentrations for St. John’s Road West week 14 (second week of full lockdown) 2020 and previous years 2019

 Fig 5 NOx air quality

 

Figure 5 Average NO2 concentrations for Cork South Link Road week 12 (one week before full lockdown) 2020 and previous years 2016 - 2019

 Fig 6 NOx air quality

 

Figure 6 Average NO2 concentrations for Cork South Link Road week 14 (second week of full lockdown) 2020 and previous years 2016 - 2019

 Fig 7 NOx air quality

 

Figure 7 Average NO2 concentrations by week for 2020 (ytd) for Pearse St. and St. John's Road West

 

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.

There is now an emerging trend of increasing air pollution at many of our monitoring stations coinciding with the easing of restrictions, however concentrations of NO2 are still below levels for this time of year, compared to previous years.

We will continue to analyse nitrogen dioxide concentrations over the coming weeks to monitor this trend.

Notes:

  • All of our hourly air quality data is on our website (http://www.epa.ie/air/quality/)
  • 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, Climate Action, and Environment, 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.