By David Shukman
Environment correspondent, BBC News
Pollution 'higher risk' to children
Children may be at greater risk from the microscopic particles in traffic pollution than was previously thought.
Early findings from a major study in London seen by the BBC show that the lung capacity of 8- and 9-year-olds is 5% lower than the national average.
And 7% of the children - surveyed in the Tower Hamlets area - have lung function reduced to a level internationally regarded as hazardous.
The London study is being led by Professor Jonathan Grigg.
He works out of the Centre for Paediatrics at Barts and the London School of Medicine and Dentistry.
The particles - so-called "particulates" - are produced in vehicle exhaust and are far smaller than the width of a human hair.
Less than 10 microns across, they are often referred to as PM10.
The results come as researchers at Lancaster University warn that levels of particulates are often higher than shown by official monitoring devices.
Analysing the particulates collected on roadside leaves, the research shows that the pollution can be most intense at the height of many children.
Britain already faces penalties from the European Union for multiple breaches of standards for particulate pollution.
Professor Grigg told BBC News: "Our findings in the East End of London are that children living here have slightly lower lung function than what we'd expect from the national average.
"Now, if that's due to air pollution, as we suspect, they're going to be at increased risk from a range of respiratory disorders such as asthma and infection, and may be at risk in adulthood."
A total of 203 children at 10 different schools are taking part in regular tests over several years.
Interim findings from 149 children show that 11 of them have lung capacity that is 80% or lower than the national average - a threshold regarded by researchers as vulnerable to a range of breathing conditions.
One test involves encouraging the children to cough - so the carbon content of their sputum can be analysed.
Microscope analysis shows how particulates are reaching deep into the lungs.
These results will add pressure on the government over Britain's failure to meet European Union air quality standards.
The EU requirement is for average PM10 concentrations to stay below 40 micrograms per cubic metre of air - but most of the country's major conurbations record higher levels.
And the new research by Lancaster University shows that the particulate levels may be even worse than official figures show.
The official data is gathered at automatic monitoring stations which typically sample air at a height of three metres - mainly to avoid the risk of vandalism.
But Professor Barbara Maher and her team have devised a new technique for measuring the magnetic response of particulates on roadside leaves - many of the particles contain fragments of metal.
Barbara Maher from Lancaster University offers her tips on avoiding traffic pollution
And the readings show higher concentrations of particulates at lower levels.
Interviewed beside a busy road in Lancaster, Professor Maher said: "We're surrounded by this invisible mist of these millions of toxic particles - you can't see them but we know, we've measured them, they're here.
"When we do our leaf magnetic measurements, our research shows that down at small child height the concentrations - the number - of these very fine particles is sometimes twice the current EU regulation standard."
One set of measurements, outside the Cathedral School in Lancaster, revealed particulate levels that were above the EU standard.
The school's head, Anne Goddard, said the findings were "quite worrying".
"It's the only playground we have at the school and it's right next to the road. The levels are high so obviously the effect on the children, especially those with asthma, is a concern."
The Environment Secretary Hilary Benn admits there is a problem but says 24 out of 27 members of the European Union are in breach of the standards and that most of the landmass of Britain does meet the requirements.
He also said that "huge progress" had been made in the last few decades with the Clean Air Act and changes in vehicles standards.
"But we need to do more and principally that will be about cars and lorries and buses," he said.
"And we've been working with other countries in Europe to improve the standards to get these PM10 particles down because we know it has an effect on our health."
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