About this data

Source: Defra, Air quality statistics in the UK, 1987 to 2025

• The Daily Air Quality Index runs from 1 (low) to 10 (very high). 'Moderate' is band 4 or above, the level at which people with heart or lung conditions may notice effects.
• A day counts towards 'Any pollutant' if at least one pollutant reached 'Moderate' or higher. Each line is an average over the stations that measure it: ozone is measured at fewer urban stations (57 in 2025), often where ozone is high, while 'Any pollutant' averages over all urban stations, so it can be lower than ozone alone. Sulphur dioxide is included in 'Any pollutant' but is not shown separately, as it almost never reaches 'Moderate' at urban stations.
• Ozone peaks on hot, sunny days, so its count varies a lot with the summer weather.
• Measurements come from the Automatic Urban and Rural Network (AURN), the UK's highest-quality network of air quality monitoring stations. Each line is the average across all stations of that type that met the data capture threshold that year.

This chart appears in Air pollution.