When the smog hangs heavy in the city it is poisoning the population that breathes it. The first report to measure the effects of air pollution in Britain concludes that its immediate effect is to hasten the deaths of between 12,000 and 24,000 vulnerable people and to trigger up to 24,000 hospital admissions each year.
This is certain to be an underestimate, because the report does not take account of the long-term effects of living in polluted cities. That is to be the subject of a further study.
The findings, by the Committee on Medical Effects of Air Pollutants, a government advisory body, indicate a more serious problem than expected. Launching the document yesterday, Frank Dobson, the Secretary of State for Health, flanked by Michael Meacher, the Environment Minister, and Sir Kenneth Calman, the Chief Medical Officer, said: "This report clearly confirms that air pollution damages health."
The findings triggered immediate demands for a cut in road traffic. The British Medical Association warned: "The grim reaper comes early on days of heavy air pollution." Friends of the Earth said the deaths figure was "extremely alarming" and the British Lung Foundation described it as "very serious".
Professor Stephen Holgate, chairman of the committee, said he had been surprised by the size of the effect. He said that although the worst effects of pollution were on those who were frail, elderly or sick, there was growing evidence that healthy individuals were affected too.
"Respiratory infections are getting worse. Air pollution reduces the capacity of the lung to combat viruses and possibly bacteria. Whether this is because of air pollution outside or inside the home needs to be sorted out," he said.
Sir Kenneth Calman sought to reduce alarm by emphasising that it was people who were already seriously ill with chronic respiratory disease who were most at risk. "They are not dying because of air pollution, they are dying because the contribution of air pollution to their ill health tips the balance."
He said they were not necessarily extra deaths or hospital admissions but ones that had been "brought forward", in some cases by a few days, but in other cases by a "somewhat longer period". He compared the effect with that of the cold in winter, which is linked with 30,000 extra deaths.
Mr Meacher said the findings contained a "major lesson" for transport. A White Paper will set out proposals to reduce car use and technical measures to cut pollution. The AA, the motoring organisation, said drivers should not be made scapegoats for poor air quality and claimed that toxic exhaust gases were down 22 per cent compared with 1992.
The report, Quantification of the Effects of Air Pollution on Health in the UK, says pollution has three effects: many chemicals, such as sulphur dioxide and ozone, act as irritants to the bronchial tubes of the lung. Some, such as nitrogen dioxide and ozone, release substances that damage the lung lining. Together these cause inflammation, irritation and make the lung less efficient at fighting infection.
Particulates, the tiny particles produced mainly by the burning of diesel fuel, are the most dangerous.
Professor Jon Ayres, a committee member, said it was likely that pollution had long-term effects on health but these remained to be proved. "What we would like to know is if you live in a town like London all your life, is it significantly shortened compared with living in a rural area. That is the big question."