A4: Rural background concentrations of ozone (O3)

Short Description

This indicator tracks changes in rural background concentration of 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

Data on the measured concentrations of O3 from the ARUN are published annually as National Statistics; Air Quality Statistics.

Indicator components

Figure A4: Rural background concentrations of ozone (O3) in England, 1987 to 2021

Table A4: Rural background concentrations of ozone (O3) in England, 1987 to 2021

Year 95% confidence interval lower bound 95% confidence interval upper bound Annual average maximum daily 8-hour mean O3 concentration (µg/m3)
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 68.63 72.07 70.35

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 25%, from 56.2 micrograms per cubic metre (μg per m3) in 1987 to 70.3 μg per m3 in 2021. 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

Rural background concentrations of O3 showed little or no change over the short and medium-term assessment periods. However, there has been an increase (deterioration) in rural background concentrations of O3 over the long term.

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 4 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 (µg/m3) Short term 2015 to 2020 4.47 Loess Deterioration
A4 Annual average maximum daily 8-hour mean O3 concentration (µg/m3) Medium term 2010 to 2020 5.31 Loess Deterioration
A4 Annual average maximum daily 8-hour mean O3 concentration (µg/m3) Long term 1987 to 2020 14.98 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.

Indicator Metadata