Ministers hope to drastically raise the acceptable threshold for nitrogen oxides (NOx), one of the most important types of pollutant gas. At present, NOx levels of lower than 50 parts per billion in air are classed as ``very good.'' The proposal is to set this threshold three times as high, at 150 parts per billion.
At the other end of the scale, when NOx levels rise above 125 ppb, air quality is presently described as ``poor''. But the Department of the Environment proposes this threshold should more than double to 300 ppb. The pollutant comes mainly from traffic exhaust and power stations and can cause severe problems for asthmatics.
A spokesman said: "The suggested new thresholds are strongly health- based, using advice from two independent expert panels."
The current banding system covers three different air pollutants - NOx, sulphur dioxide and ozone - and classifies air quality for each of them as "very good", "good'', "poor" and "very poor". The proposed new system will add two more pollutants, carbon monoxide and particulates, and the bands will become "very good", ``moderate or generally satisfactory'', "poor" and "very poor".
The Government says that low pollution levels in the ``very good'' band are unlikely to have harmful effects, even on people who are sensitive to dirty air such as those withrespiratory diseases. The lowest thresholds are the same as those set out in the Government's air quality strategy. They are levels which are frequently exceeded now but which hopefully will not be by 2005.
For pollution levels classed as "moderate" or "generally satisfactory'' under the proposals "there could be a small risk of effects in sensitive individuals", said the department.
But Dr Malcolm Eames of the National Society for Clean Air rejected this new band. He said classifying air quality as "generally satisfactory'' when it fell below the Government's own health-based standard ``would cause considerable public confusion'.'
The inclusion of microscopic particulates, now thought of as the most dangerous type of pollution, in the information service will mean that big cities are all likely to have at least one or two days with ``very poor'' air quality each year. Belfast, which has UK's dirtiest air, would have had 20 such days using the new categories, in 1995.
t Exhaust-cleaning catalytic converters are to be fitted to 250 of London's Routemaster buses - the oldest and most polluting type used in the capital, it was announced yesterday. The change will bring the veteran vehicles up to modern exhaust fume standards.Reuse content