By Paul Rincon
BBC News Online science staff, at the BA festival
The UK will fail to meet key objectives on reducing air pollution, resulting in further damage to human health, a leading expert has said.
Road traffic is a major contributor to air pollution
Professor Mike Pilling said levels of nitrogen dioxide, small particles and ozone were too high for official targets for 2005 and 2010.
Air pollution causes several thousand deaths and hospital admissions each year, mainly in the elderly.
Research results are being presented at the BA Festival of Science in Exeter.
The targets set by the government are closely linked to similar limits set by the European Union (EU). Most big EU cities are also likely to fail to make their targets.
Professor Pilling, of the Air Quality Strategy group, said London was a particular problem.
"London in particular is going to show [excess levels of] nitrogen dioxide and particulate matter," he explained at the British Association's annual meeting.
A key pollutant, nitrogen dioxide, is formed by the action of sunlight on compounds such as nitric oxide, which is emitted directly from petrol and diesel vehicles.
Professor Pilling said that, clearly, a significant contributor to this failure to meet objectives was traffic - but this was not the only contributor.
Particulate matter is the term given to a range of dusty matter - produced by a variety of different processes, both human-produced and natural - which is thought to be harmful to human health.
"We're used to thinking of air quality as a local issue or a regional issue, but it's becoming increasingly clear that it's a global issue," he said.
Professor Pilling explained that pollutants and their precursor molecules are drifting over to the UK from America.
These global-scale processes are probably contributing to the steadily rising background concentrations of ozone.
These are even rising in clean areas such as western Ireland.
One of the reasons for this was the inter-continental transfer of pollutants, Professor Pilling explained.
The highest concentrations of ozone occur in summer. August 2003 saw a particularly severe ozone episode which caused a photochemical smog.
About 2,000 deaths in England have been attributed to the heatwave and it is estimated that 25-40% of these resulted from poor air quality.
Projections suggest the frequency of these heatwaves may increase 10-fold by 2070.
"The way we tackle air quality at the moment is through a series of independent objectives," said Professor Pilling.
"We try to reduce the concentrations of particulate matter. We try to reduce concentrations of nitrogen dioxide.
"It's becoming clear we need to treat it from a perspective of how these different pollutants interact with each other. Some increases in nitrogen dioxide may lead to increases in ozone."