A5: Roadside nitrogen dioxide (NO2) concentrations
Short Description
This indicator tracks changes in average roadside concentration of nitrogen dioxide (NO2). NO2 arises predominantly from combustion sources such as traditionally fuelled vehicles and therefore the highest concentrations are often found at roadside locations.
This indicator is an assessment of clean air (reporting the condition of the atmosphere as an asset). Exposure to NO2 can also be considered as a pressure on human health. The indicator is determined by calculating the average value of the annual mean concentrations measured across Defra’s Automatic Urban and Rural Network (AURN) at all roadside locations (with greater than 75% data capture in any one year).
Readiness and links to data
UK data on the measured concentrations of NO2 from the AURN, together with an annex containing the summary data for roadside monitoring sites in England, are published annually as National Statistics; Air Quality Statistics. Depending on when these data are accessed, they may differ from the data appearing in this indicator because of differences in the timing of annual updates and because there can be minor changes to the time series following further data ratification and quality assurance checks. For more information on these please see: Automatic Urban and Rural Network (AURN) - Defra, UK.
Indicator components
Figure A5: Roadside nitrogen dioxide (NO2) concentrations in England, 1997 to 2022
Table A5: Roadside nitrogen dioxide (NO2) concentrations in England, 1997 to 2022
| Year | 95% confidence interval lower bound | 95% confidence interval upper bound | Annual mean NO2 concentration |
|---|---|---|---|
| 1997 | 50.60 | 68.83 | 59.72 |
| 1998 | 48.47 | 68.02 | 58.24 |
| 1999 | 52.69 | 70.01 | 61.35 |
| 2000 | 48.04 | 64.79 | 56.42 |
| 2001 | 47.10 | 61.47 | 54.29 |
| 2002 | 44.29 | 59.21 | 51.75 |
| 2003 | 47.94 | 68.97 | 58.45 |
| 2004 | 46.04 | 65.02 | 55.53 |
| 2005 | 48.41 | 67.30 | 57.86 |
| 2006 | 47.72 | 68.78 | 58.25 |
| 2007 | 47.68 | 70.44 | 59.06 |
| 2008 | 42.45 | 64.51 | 53.48 |
| 2009 | 38.98 | 57.17 | 48.07 |
| 2010 | 39.35 | 56.57 | 47.96 |
| 2011 | 35.03 | 52.72 | 43.88 |
| 2012 | 34.55 | 50.55 | 42.55 |
| 2013 | 33.26 | 48.80 | 41.03 |
| 2014 | 31.16 | 48.88 | 40.02 |
| 2015 | 29.71 | 42.10 | 35.90 |
| 2016 | 32.85 | 42.81 | 37.83 |
| 2017 | 29.57 | 36.96 | 33.26 |
| 2018 | 28.66 | 35.92 | 32.29 |
| 2019 | 27.66 | 33.13 | 30.40 |
| 2020 | 20.96 | 25.05 | 23.00 |
| 2021 | 22.54 | 26.76 | 24.65 |
| 2022 | 21.61 | 25.98 | 23.79 |
Trend description for A5
Average roadside NO2 concentrations in England have fallen considerably from 59.7 micrograms per cubic metre (μg per m3) in 1997 to 23.8 μg per m3 in 2022, a drop of 60.2% over the latest 25 years for which data are available. The general trend in measured NO2 concentrations is decreasing and the average value falls below the NO2 limit of 40 μg per m3 in recent years. However, there was a slight increase in 2021 following the lifting of COVID-19 lockdown restrictions as the time series reached its lowest point in 2020 because of an unusually low level of road traffic. There are also hotspots of NO2 exceedances across England, which are being addressed through the NO2 plans.
Assessment of change
Average roadside NO2 concentrations have decreased (shown an improvement) over the short, medium and long-term assessment periods. Compliance with legal NO2 limits is assessed at individual locations rather than using the England average recorded by this indicator, so it would not be appropriate to use results from this indicator to establish whether targets have been met.
More information on trends and monitoring at a regional level can be found in the Air Pollution in the UK report.
Change since 2018 has also been assessed. A decrease (improvement) in roadside NO2 concentrations was observed since 2018. However, this is based on only 5 data points and 2 of these (2020 and 2021) have been heavily influenced by COVID-19, so this result should be considered as indicative and not evidence of a clear trend.
Further information on this assessment, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results pages.
Table A5: Assessment of change
| Component | Subcomponent | Period | Date range | Percentage change | Smoothing function | Assessment of change |
|---|---|---|---|---|---|---|
| A5 | Annual mean NO2 concentration | Short term | 2016 to 2021 | -29.37 | Loess | Improvement |
| A5 | Annual mean NO2 concentration | Medium term | 2011 to 2021 | -45.39 | Loess | Improvement |
| A5 | Annual mean NO2 concentration | Long term | 1997 to 2021 | -57.45 | Loess | Improvement |
Note that assessment categories for short, medium and long term were assigned based on smoothed data, so percentage change figures in Table A5 may differ from unsmoothed values quoted elsewhere. Percentage change refers to the difference seen from the first to last year in the specified date range.