Tube air quality ‘up to 30 times worse’ than above ground

Whilst most of Mayor Khan’s air pollution strategy has focused above ground, a report commisioned by Transport for London (TfL) has revealed that levels of pollution on the London Underground are up to 30 times worse than the streets above.

In the first study of its kind since 1998, the Committee on the Medical Effects of Air Pollutants (Comeap) studied air quality on the network, which carries 4.8m journeys every day.

Particulate matter (PM) emission sources in the London Underground are different from those contributing PM to ambient air and the physical and chemical properties of the emitted particles are also different.

However, the report states that they ‘cannot rule out the possibility that there is a health risk from exposure to underground PM.’

‘Given that 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,’ it added.

Their research revealed that the Northern Line had the largest concentration of PM2.5 with the air on platforms at Hampstead station — the furthest station beneath ground level — recording an average 492 micrograms per cubic metre (μg/m3) of air, compared with an annual average of 16 μg/m3 from a roadside monitoring site in London.

Mass concentrations of PM at the platforms on London Underground lines are typically much higher than in ambient air, according to the report. Researchers put this down to the system’s age (it is the world’s oldest subway system) and the fact that large parts of the network are in deep, poorly ventilated tunnels.

Comeap’s recommendations to TfL include enabling London Underground PM to be included in wider toxicity studies, conducting additional measurements of metal concentrations and to continue PM monitoring to allow better understanding of concentrations as well as factors affecting PM concentrations and exposure, including passenger numbers, ventilation, train piston effect and station design.

Peter McNaught, director of asset operations at TfL, said: ‘It is vital that we operate with the very latest understanding of the risks arising from particles in the air, which is why we commissioned Comeap to undertake this research.

‘Although the report emphasises further monitoring and research is needed, it is an important contribution to the study of health effects associated with dust exposure. We are committed to maintaining the cleanest air possible for our staff and customers when using the Tube.’

Read the report here

A report published last year argued that using overground transport routes, instead of London’s Underground network, could cut exposure to air pollution for commuters travelling into and out of the capital, research has suggested.

This was among the recommendations in a study carried out by King’s College London’s Environmental Research Group on behalf of the Northbank Business Improvement District, looking at the particulate air pollution exposure characteristics of workers commuting into the area on a daily basis.