A4: Rural background concentrations of ozone (O3)
Short Description
This indicator tracks changes in rural background concentration of ground-level ozone (O3). Chemical reactions in the air involving nitrogen oxides (NOx) and volatile organic compounds (VOCs) produce the toxic gas O3 which can harm health, damage wild plants, crops, forests, and some materials, and is a greenhouse gas contributing to global warming.
This indicator is an assessment of clean air (reporting the condition of the atmosphere as an asset). Exposure to O3 can also be considered as a pressure on human health and thriving plants and wildlife. The indicator is determined by calculating the annual average of the maximum daily 8-hour mean concentrations of O3 measured at all rural measurement sites on Defra’s Automatic Urban and Rural Network (AURN).
Readiness and links to data
UK data on the measured concentrations of O3 from the AURN, together with an annex containing the summary data for rural background 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 this, please see: Automatic Urban and Rural Network (AURN) - Defra, UK.
Indicator components
Figure A4: Rural background concentrations of ozone (O3) in England, 1987 to 2022
Table A4: Rural background concentrations of ozone (O3) in England, 1987 to 2022
| Year | 95% confidence interval lower bound | 95% confidence interval upper bound | Annual average maximum daily 8-hour mean O3 concentration |
|---|---|---|---|
| 1987 | 37.85 | 74.54 | 56.20 |
| 1988 | 56.14 | 71.21 | 63.67 |
| 1989 | 58.76 | 74.80 | 66.78 |
| 1990 | 62.40 | 75.61 | 69.01 |
| 1991 | 60.06 | 74.96 | 67.51 |
| 1992 | 58.99 | 74.86 | 66.93 |
| 1993 | 55.98 | 72.27 | 64.12 |
| 1994 | 63.92 | 74.52 | 69.22 |
| 1995 | 64.42 | 75.28 | 69.85 |
| 1996 | 61.52 | 70.57 | 66.04 |
| 1997 | 61.50 | 70.35 | 65.93 |
| 1998 | 62.59 | 70.92 | 66.75 |
| 1999 | 67.73 | 75.07 | 71.40 |
| 2000 | 63.30 | 70.43 | 66.87 |
| 2001 | 62.37 | 70.00 | 66.18 |
| 2002 | 63.61 | 70.31 | 66.96 |
| 2003 | 69.57 | 77.12 | 73.34 |
| 2004 | 69.03 | 74.25 | 71.64 |
| 2005 | 66.15 | 73.27 | 69.71 |
| 2006 | 69.79 | 77.63 | 73.71 |
| 2007 | 64.19 | 70.06 | 67.12 |
| 2008 | 65.40 | 71.02 | 68.21 |
| 2009 | 63.07 | 70.03 | 66.55 |
| 2010 | 62.58 | 70.48 | 66.53 |
| 2011 | 63.59 | 70.15 | 66.87 |
| 2012 | 61.41 | 67.39 | 64.40 |
| 2013 | 64.78 | 70.10 | 67.44 |
| 2014 | 65.58 | 71.96 | 68.77 |
| 2015 | 67.80 | 72.90 | 70.35 |
| 2016 | 64.00 | 68.35 | 66.18 |
| 2017 | 65.66 | 71.09 | 68.37 |
| 2018 | 69.94 | 74.88 | 72.41 |
| 2019 | 69.07 | 74.56 | 71.82 |
| 2020 | 70.18 | 75.16 | 72.67 |
| 2021 | 68.61 | 72.05 | 70.33 |
| 2022 | 71.43 | 76.28 | 73.85 |
Trend description for A4
The average daily maximum 8 hour mean concentration of O3 has fluctuated considerably since the time series began, but overall it has increased by 31.4%, from 56.2 micrograms per cubic metre (μg per m3) in 1987 to 73.9 μg per m3 in 2022. Some variance from year to year is expected due to fluctuations in the occurrence of hot summer weather conditions which are associated with high O3 concentrations.
Assessment of change
There has been an increase (deterioration) in rural background concentrations of O3 over the short, medium and long-term assessment periods.
Change since 2018 has also been assessed. Little or no change was observed for rural background concentrations of O3 since 2018. However, this is based on only 5 data points so 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 A4: Assessment of change
| Component | Subcomponent | Period | Date range | Percentage change | Smoothing function | Assessment of change |
|---|---|---|---|---|---|---|
| A4 | Annual average maximum daily 8-hour mean O3 concentration | Short term | 2016 to 2021 | 5.34 | Loess | Deterioration |
| A4 | Annual average maximum daily 8-hour mean O3 concentration | Medium term | 2011 to 2021 | 7.05 | Loess | Deterioration |
| A4 | Annual average maximum daily 8-hour mean O3 concentration | Long term | 1987 to 2021 | 16.61 | Loess | Deterioration |
Note that assessment categories for short, medium and long term were assigned based on smoothed data, so percentage change figures in Table A4 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.