Up to a third of new childhood asthma cases in Europe could be caused by air pollution, a study found.
Hundreds of thousands of children aged between one and 14 are believed to fall ill by breathing in pollutants each year, researchers estimate.
Around 1.1million children are believed to suffer from asthma in the UK.
It is thought traffic pollution can damage airways, leading to inflammation and the development of asthma in children who are genetically predisposed to the condition.
The Barcelona Institute for Global Health (ISGlobal), which led the study, looked at the burden of asthma on 63,442,419 children across 18 European countries, including the UK, in 2016.
They compared asthma incidence rates with estimations of levels of exposure to pollutants in more than 579 sq/m (1.5m sq/km) areas in 2010, which are often traffic-related in urban areas.
Finally they estimated how rates could be affected if levels were reduced in two different scenarios.
They found that, each year, 11.4% of the total cases of asthma (66,567) could be prevented if countries adhered to maximum air pollution levels of PM2.5 recommended by the World Health Organisation.
This equates to more than 10,000 cases in the UK being prevented annually.
But only 0.4% (2,434 cases) across the countries would be prevented with the reduction of another pollutant, nitrogen dioxide (NO2), which is a better marker of traffic sources.
Researchers believe these guidelines are outdated and need to be lowered.
Tens of thousands more cases of childhood asthma could be avoided if countries went further, researchers predict.
In the UK, 44,895 cases (29% of the UK total) could be avoided if the country reduced air pollution to the lowest levels recorded in 41 previous studies.
And 191,883 cases (33%) could be avoided each year across the 18 European countries in the study.
For the N02 pollutant, 135,257 (23%) could be stopped if the countries adhered to the lowest levels – 40,000 of which were in the UK (26% of the UK total).
If black carbon, a third pollutant, was reduced to the lowest levels it would mean 19,139 UK cases and 89,191 cases across the 18 countries could be avoided annually.
Professor Mark Nieuwenhuijsen, an author of the study from the Barcelona Institute for Global Health, said “major lifestyle changes” in the UK would be needed to reach the lowest levels, recorded in Scandinavian countries.
He said: “A lot of the air pollution we have comes from cars, residential cooking and heating, industry and ports, so what you need to get rid of is the fossil fuels that produce all this pollution.
“And besides that what you also might want to look at is a reduction of cars in cities because even if you get electric cars, if they run on renewable energy, you still have particulate matter coming from the brakes, tyres and the wear and tear of the car – it will reduce NO2 levels, but only 50% or so of the PM2.5 levels.
“So you are also looking towards a reduction of cars and a move towards public transportation, cycling or walking.”
The study, published in the European Respiratory Journal, concluded: “Our estimates are larger than previous documentation and underline the urgent need to reduce children’s air pollution exposure across Europe.”
A previous study in The Lancet Planetary Health suggested that just under a fifth of new childhood asthma cases in the UK could be linked to NO2 traffic pollution.
Ella Kissi-Debrah, who lived near the South Circular Road in Lewisham, southeast London, died in 2013 after having an asthma attack.
The nine-year-old’s death will be re-examined at an inquest, to determine whether it was linked to air pollution.
Rosamund Adoo-Kissi-Debrah, her mother, said in response to the latest findings: “(This is) another reminder that the government are not taking the health impacts of air pollution seriously enough.”
She added: “Our new prime minister can show the nation he is serious about the public health crisis by putting money into a health campaign.
“I believe the nation would rather have an informative campaign (about) how to protect their health against air pollution rather than a no-Brexit campaign, especially when it is a matter of life and death.”
Dr Samantha Walker, director of policy and research at Asthma UK, said: “This research is yet another reminder that the government needs to tackle air pollution as an urgent priority and commit to meeting air quality standards from the World Health Organisation in its upcoming environment bill.
“No child should face the risk of getting asthma or having a life-threatening asthma attack because of filthy air.”
A government spokeswoman said: “Air quality has improved significantly in recent years, but air pollution continues to shorten lives which is why we are taking concerted action to tackle it.
“We are working hard to reduce transport emissions and are already investing £3.5billion to clean up our air, while our clean air strategy has been commended by the World Health Organisation as an ‘example for the rest of the world to follow’.
“Our environment bill will give legal force to that strategy and put environmental accountability at the heart of government.”