MILLIONS of visits to A&Es for asthma every year across the globe may have been triggered by polluted air, according to a study.

The research, from George Washington University in Washington DC, estimates that up to 33 million visits to emergency departments for asthma could have been caused by pollutants entering the lungs.

It is the first study to estimate the impact of air pollution on asthma cases across the globe.

The study comes in the wake of a Government report which revealed that Bolton has some of the most polluted roads in Greater Manchester.

Sections of St Peter's Way, together with parts of Deane Road, Trinity Street, St George's Road and Bradford Street will breach legal limits for harmful nitrogen oxide by 2020 unless action is taken, the report says.

Susan Anenberg, lead author and associate professor at the George Washington University's Milken Institute School of Public Health, said policies to clean up the air could reduce the burden of asthma and improve respiratory health.

In particular, Dr Anenberg said targeting emissions from cars in big cities would not only aid people with asthma and other respiratory diseases but would help everyone breathe a little easier.

She added: "Millions of people worldwide have to go to emergency rooms for asthma attacks every year because they are breathing dirty air.

"Our findings suggest that policies aimed at cleaning up the air can reduce the global burden of asthma and improve respiratory health around the world."

Greater Manchester's lead of public health for air quality, Eleanor Roaf, said: "Air pollution is the number one environmental public health issue in Greater Manchester.

"And it's children, older people and those in poor health who are hit the hardest by polluted air."