City air pollution 'will get worse'

CATALYTIC converters on cars are likely to cause higher levels of one type of air pollution in cities, a Government committee will report this week.

The Quality of Urban Air Review Group's first report, of which the Independent on Sunday has obtained a summary, says that although the introduction of 'cats' should improve air quality by removing some pollutants, they will increase concentrations of ozone in urban areas. Although ozone gas shields the earth from ultraviolet light high in the stratosphere, at ground level it is a pollutant that irritates the eyes and the lining of the lungs.

Ministers have been hoping that air quality will be improved by fitting catalytic converters on car exhausts. Under EC rules they were to have been compulsory on all new cars from the end of this year. However, the Government has granted a one-year extension because of large stocks of unsold cars without converters.

Catalytic converters remove carbon monoxide, hydrocarbons (including benzene) and nitric oxide from exhaust fumes. But the forecast growth in traffic - a doubling by 2025 - is likely to overwhelm even these the gains, the report predicts.

However, though nitric oxide is undesirable in the atmosphere because it goes through a series of reactions in air to become nitrogen dioxide (NO2 ), a pollutant known to cause breathing difficulties, this does have one desirable side effect. The chemical reactions help remove ozone from the air.

Health guideline levels for ozone are regularly breached in Britain during summer, although the concentrations tend to be highest in the countryside because nitric oxide produced by traffic lowers urban levels.

The review group, made up of civil servants and scientists, was set up after the 1990 White Paper on the Environment. Its report will be published on the 40th anniversary of the London 'peasouper' that caused the death of 4,000 people. The notorious smogs before the Clean Air Acts were caused by a combination of coal burning and temperature inversion - a common winter phenomenon in which still, cold air is trapped for days. High levels of lung-damaging sulphur dioxide and dust built up. The review group's report says that invisible smogs caused by traffic are now returning to Britain's cities.

The worst, which occurred exactly a year ago, was also associated with a temperature inversion and lasted four days. On 13 December 1991, London experienced the most severe nitrogen dioxide and benzene pollution since regular monitoring began in 1971. Benzene is a carcinogen, although it is not proven that it causes cancer at the levels found in smogs.

The report says that levels of NO2 , carbon monoxide and occasionally sulphur dioxide, exceed international health guidelines in urban areas. If Britain was not a windy country the pollution would be worse.

The group's chairman, the atmospheric chemist Professor Roy Harrison of Birmingham University, said: 'We need an integrated transport policy with improved public transport. It's a view which I think is slowly getting through to government.'

Professor Harrison said it was not known whether the smog a year ago caused a wave of illness. A preliminary survey found no jump in hospital admissions. However many asthmatics may have coped by using their inhalers more.

Tomorrow the Government will also issue a discussion document on how to meet emissions targets agreed at the Rio conference in June. A carbon tax will be one option.