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London Tube: Does Its Air Harm Your Health?

BBC Science Focus

March 2022

The Mayor of London hopes that 80 per cent of trips in the city will be made on foot, bike or public transport by 2041. But how polluted is the Underground's air?

- By Amy Barrett. Photographs by NASA, ESA and Shutterstock

London Tube: Does Its Air Harm Your Health?

On any given weekday, the London Underground can see up to five million passengers hopping on and off. Its 11 lines serve 272 stations, and at peak times there can be more than 500 trains hurtling around beneath the streets of London. As it's been in constant use since the 19th Century, the London Underground has remained largely the same, and hasn't been updated or researched as much as other forms of transport.

The pandemic did provide Transport for London (TFL), which manages the London Underground, the opportunity to make some improvements. Ventilation systems were assessed and, according to the Mayor's Transport Strategy Update in 2021, the London Underground ventilation infrastructure is typically designed in excess of statutory minimum requirements with an adequate provision of fresh air. But how fresh is the air you're breathing on the Tube?

The air, even before it gets to the Underground, isn't perfectly clean,” explains Dr David Green, who leads the aerosol science team at Imperial College London and is a member of the UK's Committee on the Medical Effects of Air Pollution (COMEAP). Green is also part of a group commissioned by TfL to regularly assess the COVID-19 risk on the Underground.

The urban background air already has a low level a of particulate matter, but on top of that you have all these extra emissions [coming from the Tube),” he adds.

These include particles that come from the carriage moving along the rails, the brake blocks rubbing on the wheels, and the electrical connection between the collector plate and the live rail. There are also particles that come from Tube passengers, human and otherwise. Hair and skin cells, plastic fibres from clothing, and debris from the creatures that call the Underground their home all contribute to the air quality.