A4: Rural background concentrations of ozone (O3)

Final Final

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). It can also be considered as a pressure on human health and thriving plants and wildlife. It 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).

Data are already published annually as National Statistics, Air Quality Statistics.

Trend description

The average daily maximum 8 hour mean concentration of ozone has fluctuated since the beginning of the time series in 1987. It was 72 μg/m3 in 2019; a 28% increase in concentration compared to 1987 but a slight decrease in concentration compared to 2018 (74 μg/m3). Some variance from year to year is expected due to fluctuations in the occurrence of hot summer weather conditions which are associated with high ozone concentrations.


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This table provides metadata for the interim or final indicator presented above.

Indicator name

Rural background concentrations of ozone (O3)

Indicator reference


Outcome Indicator Framework theme


Headline indicator status

Not applicable

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
Geographic scope


Status of indicator development


Date last updated

11 June 2021