By Alex Kirby BBC News Online environment correspondent

The air in many European cities is still so polluted that thousands of people are dying premature deaths, scientists say.

They describe the damage done by poor air quality as "a significant threat to public health".

Air pollution continues to pose a significant threat to public health in urban environments in Europe

Apheis report

They found that even very small cuts in pollution can benefit health. But they recognise this is one risk individuals can do little to control.

The researchers are from a group called Apheis - Air Pollution and Health: A European Information System.

It says its mission is "to provide European decision-makers, environmental health professionals, the public and the media with an up-to-date, easy-to-use information resource... concerning air pollution and public health".

Its report, entitled A Health Impact Assessment of Air Pollution in 26 European Cities, says: "Air pollution continues to pose a significant threat to public health in urban environments in Europe, despite tighter emission standards, closer monitoring of air pollution, and decreasing levels... of certain types of air pollutants."

Life-saving reduction

Most European cities take daily measurements of particulate air pollution - caused by very small particles - with one of two techniques.

The first measures PM10 particles (those smaller than 10 micrometres), the second black smoke (with particles less than about four micrometres).

Levels are then expressed as micrograms of pollution per cubic metre (mg/m3).

Athens is one of the cities mentioned in the study

Pollution levels vary widely across Europe, with the annual average levels in the Apheis cities ranging from 14 to 73 mg/m3 for PM10, and from 8 to 66 mg/m3 for black smoke.

Levels as high as these have been shown to be a health risk.

The report says 2,653 premature deaths could be prevented every year if long-term exposure to annual average PM10 levels were cut to 40 mg/m3 in the 19 cities that measured these larger particles.

The European Commission has set 40 mg/m3 as the limit value for all member states by 2005.

The report says achieving the 20 mg/m3 limit set for 2010 would prevent 11,855 premature deaths annually.

And even a modest reduction of 5 mg/m3 in long-term exposure to outdoor concentrations of PM10 would avoid an annual 5,547 early deaths.

That saving would mean the elimination of 19 premature deaths for every 100,000 inhabitants.

Bigger than Aids

For comparison, that is almost four times the annual death rate from Aids in the countries Apheis investigated, 2.6 times the leukaemia rate, and 1.5 times the annual rate of traffic fatalities.

The authors say at least 832 of those 5,547 deaths could be prevented by cutting short-term PM10 exposure by 5 mg/m3.

They say a recently published Dutch study suggests the effects on mortality rates of long-term exposure to black smoke should be similar.

But they were obliged to look only at the acute, short-term effects.

They conclude that a cut of 5 mg/m3 in short-term exposure to outdoor black smoke concentrations could prevent almost 577 premature deaths annually in the 15 cities that measured the pollutant.

Dr Sylvia Medina of Apheis said: "Even very small and achievable reductions in air pollution levels have a beneficial impact on public health, and thus justify taking preventive action in all cities, no matter how low their levels of air pollution.

"Our findings are consistent with those of other organisations, and add one more brick in the wall of evidence that air pollution continues to have an impact on public health."

The report says individuals have little control over their exposure to pollution of this sort, but have more with other risk factors like diet and cigarette smoking.

The 26 cities examined in the Apheis report are: Athens, Barcelona, Bilbao, Bordeaux, Bucharest, Budapest, Celje, Cracow, Dublin, Gothenburg, Le Havre, Lille, Ljubljana, London, Lyon, Madrid, Marseille, Paris, Rome, Rouen, Seville, Stockholm, Strasbourg, Tel Aviv, Toulouse and Valencia.