On-train concentrations of nitrogen dioxide can peak at levels ranging from one to 13 times higher than identified next to major central London roads, according to new research.
The research, funded by the Department for Transport (DfT) and conducted by RSSB, looked at six types of train and found that the peaks most frequently occur when trains are in tunnels or idling in stations.
RSSB concluded that the quality of air on services remains within the legal workplace limit. However, the DfT acknowledged that air quality levels on some trains, while operating under diesel power, is “poorer than desired”.
In response it has commissioned a review of all the regulations and standards that currently control air pollution and people’s exposure to it on the rail network. This will include on-board services as well as in stations.
Rail Minister Chris Heaton-Harris said: "The safety of staff and passengers is our absolute priority. While these findings are within limits, I do not believe people should have to accept anything less than the highest levels of air quality.
"I have asked the industry to immediately conduct further research and explore all engineering modifications and options to rapidly improve air quality on trains and in stations.
"I have also launched a comprehensive review of the current standards and guidance related to air quality on the rail network. If required, we will not hesitate to strengthen legislation to ensure the highest standards of air quality are met and maintained."
George Davies, director of sustainable development at RSSB, said: "Collectively the rail industry and Government have been working with us through the Air Quality Strategic Framework to identify the right monitoring, modelling and mitigation.
"Our important research is helping us understand the issue in much greater depth enabling the rail industry, Government and regulator to take the necessary steps.
"We look forward to continuing this work and ensuring the rail network plays its part in addressing poor air quality."
This new review forms part of broader work by the Government to ensure passengers and staff can have confidence in air quality on their services, which includes working with stakeholders such as the Rail Delivery Group and the RSSB to trial the use of upgraded air filtration devices on passenger services.
The Government also announced in its transport decarbonisation plan that it intends to create a net zero rail network by 2050.