Travelling on the London underground for just one hour could expose you to as much air pollution as spending an entire day by a busy road, a new report suggests.

Research by the Committee on the Medical Effects of Air Pollutants looked primarily at the presence of particulate matter (PM) on the tube. It’s the first study of its kind since 1998.

The researchers found the Northern line was the most polluted, with the highest concentration of PM2.5 – particulate matter less than 2.5 micrometers in size  which is small enough to penetrate deeply into the lungs.

Platforms at Hampstead tube station, one of the deepest stations at 60m below ground level, reported levels of pollution 30 times higher than the roadside. 

An average of 4.8 million journeys are made on the London Underground every day.

In 2003, the Institute of Occupational Medicine (IOM) made several recommendations on the need for studies on the health effects of pollution in underground subway systems.

Yet there has been little progress in this area over the last 15 years. Few studies have examined the potential effects of inhalation exposure to underground PM on human health, and those that did reported inconsistent results.

Researchers have called for a reassessment on how dangerous particulate matter is to human health. Due to the lack of available studies in the area, the report’s authors said it was hard to determine the extent of risk to health.

They did say, however, that given there is “strong evidence that both long- and short-term exposure to particle pollutants in ambient air are harmful to health, it is likely that there is some health risk associated with exposure to underground PM”.

In response to the report, Peter McNaught, Transport for London’s (TfL) Director of Asset Operations, said: “It is vital that we operate with the very latest understanding of the risks arising from particles in the air.”

He said TfL is committed to maintaining the cleanest air possible for staff and customers when using the Tube.

“We closely monitor dust levels on the Tube and, through a wide range of measures, ensure that particle levels are well within Health & Safety Executive guidelines,” he said.

“We have already enhanced our sampling regime by including tests for additional metals and we will continue to investigate ways we can keep dust and particles to an absolute minimum.”

The next round of dust sampling on the underground will take place in early 2019, which will include tests for additional metal concentrations.