Appliance of science to smog alerts

The Government is moving the goal posts for a key air pollutant; levels which were described as 'poor' will now be classified as 'low pollution'. It's not as daft as it sounds, says Nicholas Schoon, Environment Correspondent .

The new system for warning people about levels of air pollution launched yesterday will give Britain a world lead, according to Michael Meacher, Minister for the Environment.

Instead of air quality being classed as either ''very good, good, poor or very poor'' based on concentrations of three gases at any one time, pollution levels will be said to be either ''low, moderate, high or very high'', based on five different gases.

Will that make any difference to wheezing asthmatics, or the drivers whose vehicles cause the bulk of the smog? Mr Meacher said the new classification is based rigorously on effects on and risks to people's health, established by extensive recent research. ''Science is driving this, not politics.''

Once pollution reaches 'moderate' levels, the Government says, ''mild effects unlikely to require action may be noticed among sensitive individuals'', which means some asthmatics, and people with other chest diseases like chronic bronchitis.

When pollution is 'high', people sensitive to pollution may suffer ''significant'' effects, and need to take action to reduce exposure by staying in. Asthmatics will need to use their inhalers more.

When levels are 'very high', people not normally sensitive to pollution may suffer eye irritation, coughing and pain on breathing deeply.

Under the old system, nitrogen dioxide levels above 100 were described as ''poor''. But now the level at which nitrogen dioxide levels shift from 'low' to 'moderate' is 150 parts per billion (ppb) and 'high' is above 300 ppb.

That means that at nitrogen oxide levels of 200 ppb - when Paris declares a major alert, bans half of all cars from the streets and makes public transport free - in London the pollution would be described as only moderate.

''What happened in Paris is not necessarily the best model for us,'' said Mr Meacher, adding that the new nitrogen oxide bands reflect the latest medical thinking.

When 'very high' levels were forecast the Government would issue an alert and ask motorists to cut unnecessary car journeys. Under the new system there would have been a total of 43 days over the past two winters when these levels were reached somewhere in Britain.

Information is available on Ceefax, Teletext, freephone (0800 556677) and at www.environment.detr.gov.uk/airq.