• How the air quality bands are calculated (before 1st January 2012)
Band Index Ozone Nitrogen Dioxide Sulphur Dioxide Carbon Monoxide PM10 Particles**
8 hourly or hourly mean* hourly mean 15 minute mean 8 hour mean 24 hour mean
 µg m-3 ppb µg m-3 ppb µg m-3 ppb mg m-3 ppm µg m-3
Low
  1 0-32 0-16 0-95 0-49 0-88 0-32 0-3.8 0.0-3.2 0-19
2 33-66 17-32 96-190 50-99 89-176 33-66 3.9-7.6 3.3-6.6 20-40
3 67-99 33-49 191-286 100-149 177-265 67-99 7.7-11.5 6.7-9.9 41-62
Moderate
  4 100-126 50-62 287-381 150-199 266-354 100-132 11.6-13.4 10.0-11.5 63-72
5 127-152 63-76 382-476 200-249 355-442 133-166 13.5-15.4 11.6-13.2 73-84
6 153-179 77-89 478-572 250-299 443-531 167-199 15.5-17.3 13.3-14.9 85-94
High
  7 180-239 90-119 573-635 300-332 532-708 200-266 17.4-19.2 15.0-16.5 95-105
8 240-299 120-149 363-700 333-366 709-886 267-332 19.3-21.2 16.6-18.2 106-116
9 300-359 150-179 701-763 367-399 887-1063 333-399 21.3-23.1 18.3-19.9 117-127
Very High
  10 360 or more 180 or more 764 or more 400 or more 1064 or more 400 or more 23.2 or more 20 or more 128 or more
* For ozone, the maximum of the 8 hourly and hourly mean is used to calculate the index value.
** Note that from August 2009 the PM10 index uses Reference Equivalent PM10 measurements.
Pollution concentrations recorded by the LAQN analysers have been classified according to Defra's Air Pollution Index system. This classes levels into bands from 'low' to 'very high'. Each band is subdivided into three to produce an Air Pollution Index, from 1 to 10, 1 being 'low', 10 being 'very high'. The concentrations are classified according to the table above. Note that different pollutants have different concentrations and averaging periods, related to the estimated health effects of each.
Read a technical explanation of how the new index bands (1st January 2012 onwards) are calculated here
See the bands for 1st Janurary 2012    Go back to the bulletin page
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