Air pollution bands

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Air Pollution Bands

Air pollution indices

Emerging EU regulation and earlier recommendations of the UK Government via Our Common Inheritance emphasised the need for greater transfer of environmental information to the public. The general public, opinion has it, feel uncomfortable with numerical data expressed in ppb, so descriptive bands or as ab air pollution index. The Department of Environment Transport and Regions publishes regular air pollution bulletins which describe pollutant concentrations in terms bands. The naming and use of bands has been a contentious issue, with the original system (which used words such as good) widely attacked by advocates of cleaner air. Mind you the current system came under assault in its openning weeks eg see Mick Hammer's article "Lies, damned lies... " New Scientist 29 November 1997, p5, although their philosophy is briefly discussed in DETR press releases it is no longer available. General DEFRA info is available from the air pollution archive. France has adopted a scale that rates air pollution with an integer in the 1-10. In North America a numerical has been defined.

The use of bands raises some difficult issues. Most immediately it is possible to argue that bands or indices are used as a mechanism for preventing access to the actual air pollution data. Quite opposite to the legislative endeavour. This can be overcome by giving the numerical values of pollutant concentration along side the bands. This can be seen on the CEEFAX air pollution pages created from DETR data.

Objection is often raised to naming air pollution bands "good", when even this good air may be polluted above natural background. The widely adopted system of assigning an index from 1-10 to pollution has the advantage of seeming free of bias. Nevertheless we are replacing one number by another, although all pollutants are normalised to a single scale. The public need to know what the numerical values mean.

We are justified in asking:

Which way does the scale run (is one or ten best)?
How are the numbers are scaled, is this with respect to concentration or the effects the pollutants have?
Do the indices account for the different averaging times required for the health effects of different pollutants?
Does the index allow for synergisms between pollutants?
Are urban particle indices applicable to forest fire particles?

Many indices seem to be based on a linear scale, yet this may not be sensible. Some have argued that the boundaries should be crossed frequently under conditions typically experienced, so that the public are aware of changes and that the air quality does not always remain at a single value. You should look at the data you worked with in the exercise on nitrogen dioxide statistics and see what kind of scale would lead to frequent changes in the index.

The boundaries create a problem in themselves as they are in effect step functions. For example it might be that a pollutant at 99ppb is falls in the class "good", yet the next day at 100ppb it falls into the class "poor". This transition would give the impression that there had been a sharp change in air quality, yet in terms of its public health impact the change would likely have been slight.