Air Quality Index Hub

United Kingdom

Daily Air Quality Index (DAQI)

Background

The United Kingdom’s Daily Air Quality Index (DAQI) accounts for five primary pollutants: PM2.5, PM10, O3, NO2 and SO2. The DAQI displays the air quality for the previous day. A forecast AQI also provides information on predicted pollutant levels for the next 5 days.

The United Kingdom Department for Environment Food & Rural Affairs (Defra) developed the Daily Air Quality Index (DAQI). Defra and the Devolved Administrations replaced the older UK Air Quality Index with the Daily Air Quality Index (DAQI) in 2012 1.

Color scale

The composite index uses a four color color scale:

1-3

4-6

7-9

10

  • Low
  • Moderate
  • High
  • Very High
Low1-3
Moderate4-6
High7-9
Very High10

Note: Adapted from “Daily Air Quality Index” (n.d.), https://uk-air.defra.gov.uk/air-pollution/daqi 2. Accessed 12 Aug. 2024.

Sub-indexes have a separate, expanded color scale:

1

2

3

4

5

6

7

8

9

10

  • Low
  • Moderate
  • High
  • Very high
Low1
Low2
Low3
Moderate4
Moderate5
Moderate6
High7
High8
High9
Very high10

Note: Adapted from “Guide to UK Air Pollution Information
Resources” (June 2014), https://uk-air.defra.gov.uk/assets/documents/reports/cat14/1406191156_060618_Guide_to_UK_Air_Pollution_Information_Resources-issue_2-FINAL.pdf 3. Accessed 12 Aug. 2024.

Methods

The sub-index DAQI values range from 1 to 10 and each correspond to a different category 3. The ‘Low’ category corresponds to index values 1 to 3, ‘Moderate’ from 4 to 6, ‘High’ from 7 to 9, and ‘Very high’ equal to 10. The DAQI is determined by the maximum concentration of the pollutants 4.

Recorded pollutant data is assigned a sub-index value 1 through 10 according to the respective pollutant concentration banding.

PollutantAveraging periodLow
1		Low
2		Low
3		Moderate
4		Moderate
5		Moderate
6		High
7		High
8		High
9		Very high
10
O3 μg/m³8 hr.0-3334-6667-100101-120121-140141-160161-187188-213214-240241+
NO2 μg/m³1 hr.0-6768-134135-200201-267268-334335-400401-467468-534535-600601+
SO2 μg/m³15 hr.0-8889-177178-266267-354355-443444-532533-710711-887888-10641065+
PM2.5 μg/m³24 hr.0-1112-2324-3536-4142-4748-5354-5859-6465-7071+
PM10 μg/m³24 hr.0-1617-3334-5051-5859-6667-7576-8384-9192-100101+

Note: Adapted from “Guide to UK Air Pollution Information
Resources” (June 2014), https://uk-air.defra.gov.uk/assets/documents/reports/cat14/1406191156_060618_Guide_to_UK_Air_Pollution_Information_Resources-issue_2-FINAL.pdf 3. Accessed 12 Aug. 2024.

The maximum sub-index is used as the overall DAQI for that station. It is reported as its respective category and corresponding color. All pollutant concentration values are rounded to the nearest whole number integer value before applying it to the concentration breakpoints 1. For the 8-hour and daily mean concentration calculations, unrounded hourly means are used 1.

References

“Daily Air Quality Index.” Department for Environment Food & Rural Affairs, uk-air.defra.gov.uk/air-pollution/daqi.

“Guide to UK Air Pollution Information Resources.” Department for Environment Food & Rural Affairs, Jun. 2024, uk-air.defra.gov.uk/assets/documents/reports/cat14/1406191156_060618_Guide_to_UK_Air_Pollution_Information_Resources-issue_2-FINAL.pdf.

“Pollution forecast.” Department for Environment Food & Rural Affairs, uk-air.defra.gov.uk/forecasting/.

“Update on Implementation of the Daily Air Quality Index. Information for Data Providers and Publishers.” Department for Environment Food & Rural Affairs, Apr. 2013, uk-air.defra.gov.uk/assets/documents/reports/cat14/1304251155_Update_on_Implementation_of_the_DAQI_April_2013_Final.pdf.

“What is the Daily Air Quality Index?” Department for Environment Food & Rural Affairs, uk-air.defra.gov.uk/air-pollution/daqi?view=more-info.

Footnotes

  1. https://uk-air.defra.gov.uk/assets/documents/reports/cat14/1304251155_Update_on_Implementation_of_the_DAQI_April_2013_Final.pdf ↩ ↩2 ↩3

  2. https://uk-air.defra.gov.uk/air-pollution/daqi ↩

  3. https://uk-air.defra.gov.uk/assets/documents/reports/cat14/1406191156_060618_Guide_to_UK_Air_Pollution_Information_Resources-issue_2-FINAL.pdf ↩ ↩2 ↩3

  4. https://uk-air.defra.gov.uk/air-pollution/daqi?view=more-info ↩