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Daily Air Quality Index

Index and Bands

In the UK most air pollution information services use the index and banding system approved by the Committee on Medical Effects of Air Pollution Episodes (COMEAP). The system uses 1-10 index divided into four bands to provide more detail about air pollution levels in a simple way, similar to the sun index or pollen index.

Low 1 2 3

Moderate 4 5 6

High 7 8 9

Very High 10

The overall air pollution index for a site or region is calculated from the highest concentration of five pollutants:

  • Nitrogen Dioxide
  • Sulphur Dioxide
  • Ozone
  • Particles < 2.5µm (PM2.5)
  • Particles < 10µm (PM10)

Air Pollution Forecasts

Air Quality Forecasts are issued on a regional basis for three different area types:

  • In towns and cities near busy roads
  • Elsewhere in towns and cities
  • In rural areas

Forecasts are based on the prediction of air pollution index for the worst-case of the five pollutants listed above, for each region.

How to use the Daily Air Quality Index

Step 1: Determine whether you (or your children) are likely to be at-risk from air pollution. Information on groups who may be affected is provided on the Additional information on the short-term effects of air pollution page. Your doctor may also be able to give you advice.

Step 2: If you may be at-risk, and are planning strenuous activity outdoors, check the air pollution forecast.

Step 3: Use the health messages corresponding to the highest forecast level of pollution as a guide.

Air pollution banding Value Accompanying health messages for at-risk individuals* Accompanying health messages for the general Population
Low 1-3 Enjoy your usual outdoor activities. Enjoy your usual outdoor activities.
Moderate 4-6 Adults and children with lung problems, and adults with heart problems, who experience symptoms, should consider reducing strenuous physical activity, particularly outdoors. Enjoy your usual outdoor activities.
High 7-9 Adults and children with lung problems, and adults with heart problems, should reduce strenuous physical exertion, particularly outdoors, and particularly if they experience symptoms. People with asthma may find they need to use their reliever inhaler more often. Older people should also reduce physical exertion. Anyone experiencing discomfort such as sore eyes, cough or sore throat should consider reducing activity, particularly outdoors.
Very High 10 Adults and children with lung problems, adults with heart problems, and older people, should avoid strenuous physical activity. People with asthma may find they need to use their reliever inhaler more often. Reduce physical exertion, particularly outdoors, especially if you experience symptoms such as cough or sore throat.

* Adults and children with heart or lung problems are at greater risk of symptoms. Follow your doctor's usual advice about exercising and managing your condition. It is possible that very sensitive individuals may experience health effects even on Low air pollution days. Anyone experiencing symptoms should follow the guidance provided on Additional Information on the Short-Term Effects of Air Pollution page.

Boundaries Between Index Points for Each Pollutant

Ozone

Based on the running 8-hourly mean. For ozone, the maximum of the 8-hourly and hourly mean is used to calculate the index value.

Index 1 2 3 4 5 6 7 8 9 10
Band Low Low Low Moderate Moderate Moderate High High High Very High
µg/m 3 0-33 34-66 67-100 101-120 121-140 141-160 161-187 188-213 214-240 241+

Nitrogen Dioxide

Based on the hourly mean concentration.

Index 1 2 3 4 5 6 7 8 9 10
Band Low Low Low Moderate Moderate Moderate High High High Very High
µg/m 3 0-67 68-134 135-200 201-267 268-334 335-400 401-467 468-534 535-600 601+

Sulphur Dioxide

Based on the 15-minute mean concentration.

Index 1 2 3 4 5 6 7 8 9 10
Band Low Low Low Moderate Moderate Moderate High High High Very High
µg/m 3 0-88 89-177 178-266 267-354 355-443 444-532 533-710 711-887 888-1064 1065+

PM2.5 Particles

Based on the daily mean concentration for historical data, latest 24 hour running mean for the current day.

Index 1 2 3 4 5 6 7 8 9 10
Band Low Low Low Moderate Moderate Moderate High High High Very High
µg/m 3 0-11 12-23 24-35 36-41 42-47 48-53 54-58 59-64 65-70 71+

PM10 Particles

Based on the daily mean concentration for historical data, latest 24 hour running mean for the current day.

Index 1 2 3 4 5 6 7 8 9 10
Band Low Low Low Moderate Moderate Moderate High High High Very High
µg/m 3 0-16 17-33 34-50 51-58 59-66 67-75 76-83 84-91 92-100 101+

Additional information for Data Providers

A report from Defra describes how the index has been implemented, including details on use of the running 24-hour mean for the latest monitoring data on UK-AIR and the use of triggers to predict air pollution episodes. This report describes updates to the thresholds used and may be of interest to air quality data providers.