Pollution from trains at London's Paddington Station means the transport hub has worse air quality than nearby major roads, a study has shown.
While UK stations are not required to comply with air quality standards, emissions from diesel engines at peak times exceeded European limits in the semi-enclosed station, the report in the journal Environmental Research Letters found.
Levels of particulates, nitrogen dioxide and sulphur dioxide - pollutants linked to health problems including lung diseases, heart conditions and premature deaths - were higher than roadside conditions at nearby Marylebone Road, the study showed.
Adam Boies, lead author of the study by researchers at the University of Cambridge and in the US, said: "We've looked at several measures of air quality.
"And we've shown that there are a number of times where the nitrogen dioxide concentrations exceed the EU hourly mean limits for outdoor air quality."
He said a relatively cheap solution may exist, adding: "Many of the trains at Paddington do not have a simple diesel particulate filter - much like you might have on your car - and these would reduce the emissions significantly."
And diesel trains are due to be replaced with electric trains as the Great Western line is electrified.
Patrick Hallgate, Network Rail's managing director for the Western route, said: "These trains will not only provide passengers with faster journeys, more seats and a more comfortable travelling experience, but they are also quieter and greener - significantly reducing noise and air pollution for passengers and our thousands of line-side neighbours."