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

Source: Department for Environment, Food & Rural Affairs, ENV02 - Air quality statistics
Unit of Measurement: Annual average maximum daily 8-hour mean (µg/m3)
Footnotes: The shaded area in the graph represents the 95% confidence interval (measure of uncertainty) for the annual mean concentration of O3 measured at rural background sites. The interval narrows over time because of an increase in the number of monitoring sites and a reduction in the variation between annual means for O3.

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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

Source: Department for Environment, Food & Rural Affairs, ENV02 - Air quality statistics
Unit of Measurement: Annual average maximum daily 8-hour mean (µg/m3)
Footnotes: The shaded area in the graph represents the 95% confidence interval (measure of uncertainty) for the annual mean concentration of O3 measured at rural background sites. The interval narrows over time because of an increase in the number of monitoring sites and a reduction in the variation between annual means for O3.

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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

Headline indicator status: Not applicable
Primary goal in the 25 Year Environment Plan: Clean air
Relevant goal(s) in the 25 Year Environment Plan: Clean air; Thriving plants and wildlife
Relevant target(s) in the 25 Year Environment Plan: Meeting legally binding targets to reduce emissions of five damaging air pollutants; Restoring 75% of our one million hectares of terrestrial and freshwater protected sites to favourable condition, securing their wildlife value for the long term
Position in the natural capital framework: Condition of assets - atmosphere
Related reporting commitments: Air Quality Standards Regulations 2010. Measurements from the UK AURN form part of the annual assessment of air quality against the limit and target values specified by this legislation
Geographical Scope: England
Status of indicator development: Final
First Reported: 2019
Last Updated: 2023
Latest Data: 2021