Pollution levels around Port Talbot revealed in a UK league table have prompted calls for a clean-up.
Air pollution in Port Talbot is causing concern
The Chartered Society of Physiotherapists (CSP) said it had not seen an improvement in air quality since it began surveys in January.
It said it was most worried about levels of the pollutant PM 10, found in diesel fumes, smoke and aerosols.
The CSP is calling for more to be done to encourage people to cut car journeys by walking or cycling to work.
The society is to call on the TUC Congress in Brighton, which is meeting this week, to lobby the government on the issue.
The CSP's call came after monitoring figures, originally published by the government agency DEFRA, showed Port Talbot had 30 microgrammes of PM10 - of soot, dust, smoke, fumes and aerosols - per cubic metre of air.
Spokesman Grahame Pope said: "We have been monitoring them for the last 18 months and been looking at what is happening to air pollution.
"This particular pollutant (PM10) is worrying, mainly because the World Health Organisation class it as a major health risk, their view is very much that there is no safe level."
Port Talbot has 40 miles of the national cycling network
Port Talbot along with Bradford, Leeds, Bury, Stockton on Tees and several parts of London feature in the UK-wide league table. Marylebone Road in London had the highest levels of pollution in the UK.
Mr Pope said he wanted to see pressure on industry to make more use of pollution-free engines.
"Fresh air is a right not a privilege. Struggling to breathe is frightening, especially for children," he said.
"No parent wants to see their children off to school in a face mask, but unless the government, car manufacturers and drivers do their bit to improve air quality, this is a possibility."
The CSP call has been backed by Sustrans Cymru, the national cycle network.
Sustrans' active travel programme manager Dafydd Thomas said Port Talbot had 40 miles of the 377-miles Celtic Trail between Monmouth and Fishguard.
He said: "If people were able to walk and cycle more, there would be fewer cars on the road and people would increase their physical activity.
"Even using public transport you are more physically active, whereas if you are sat in a car you are still exposed to pollutants but you are sitting as well."