Port Talbot has the most polluted air in Wales, according to a new study.
The problems of pollution in Port Talbot have been long known
Scientists found the industrial town had the highest rate of a pollutant linked to breathing difficulties.
They found 31 microgrammes of tiny particles known as PM10 - of soot, dust, smoke, fumes and aerosols - per cubic metre of air.
Across the UK, only Marylebone Road and Camden in London had higher levels, with readings of 43 and 35. The national average was 23.3.
With a reading of 25 microgrammes, Cardiff also figured in the worst areas for PM10 particles, which come mainly from diesel engines.
The research was collated by the Chartered Society of Physiotherapy (CSP), and a spokesman confirmed that Port Talbot was "well above the average".
Pollutant levels (microgrammes per cubic metre)
London Marylebone Road - 43
Camden - 35
Port Talbot - 31
Bury - 30
Bradford - 27
Glasgow - 27
London A3 - 27
London Hillingdon - 27
Stockton-on-Tees - 27
London Bloomsbury - 26
London Harlington - 26
Cardiff - 25
"The information that we have collected measured the amount of pollutant in the atmosphere," he said.
"Port Talbot came out at 31 units, whereas the national average for cities was 23 units."
The CSP is warning of the health risks of the pollution and said councils and governments should take greater heed of the need to reduce emissions.
Gordon James, from Friends of the Earth Cymru, described the problem was "extremely worrying".
"We've known for a long time that Port Talbot is very high to the top of the list of the most polluted areas in the UK," he said.
"We have seen a slight long-term decline in these pollutants over the year, but recent studies show the health impacts are worse than we previously thought."
He said that levels were particularly high in Port Talbot because the town "got a double whammy" because of its heavy industry and the M4 which runs alongside it.
Mr James backed schemes such as congestion charges to reduce the problem.