Improving air quality on the Tube

The Tube is the oldest metro system in the world. Similar to other underground railways, the bustling journeys of millions of passengers, the movement of trains braking and accelerating along its 250 miles of track, and continuous engineering works to keep the system running can all produce dust that accumulates in tunnels and stations. All underground networks around the world face issues with dust, and parts of London’s network are 160 years old.

Dust on the Tube is different to pollution above ground, and is made up of a mix of:

• Metal particles - most of which are iron oxide, caused by track and wheel wear and braking
• Organic matter like skin and hair
• Mineral dusts

Our monitoring shows that dust levels on the Tube remain below occupational limits set by the Health and Safety Executive (HSE), but we're not complacent.

Transport for London (TfL) has implemented an ambitious, multi-million-pound programme to reduce dust and improve air quality on the Underground network. TfL address dust through extensive cleaning and monitoring, and by exploring the latest innovations and commissioning world-leading research.

TfL take a targeted approach to reducing dust levels in the most-affected areas on the Tube networl, with specific cleaning in places where their monitoring has shown higher dust levels. TfL increased their annual Tube dust cleaning budget by a third to £2 million and have also introduced innovative new cleaning methods, including mobile backpack vacuum cleaners.

This approach is getting results. Since 2019, in-station dust levels have been reduced by 21 per cent and in the driver's cab by 14 per cent.

TfL have also commissioned more research to make sure we understand any potential health impacts as fully as possible. The first of these studies was published in March 2024.

Monitoring

TfL use an independent company to do annual air quality monitoring across the Tube network. Besides dust levels on the Tube being below HSE occupational limits, levels on most of the network are also below the recommendations from the Institute of Occupational Medicine, which are set significantly lower.

Specialist, calibrated equipment is used in this monitoring - this is likely to achieve more accurate and detailed results than personal, portable devices.

TfL’s monitoring results are available on their website under the Environment monitoring & reporting page. These are updated annually with the latest results.

People are generally only exposed to dust on the Tube for relatively short periods of time during their journeys, and levels meet the relevant regulatory standards for exposure.

At the request of TfL, the Government's Committee on the Medical Effects of Air Pollutants (COMEAP) reviewed the evidence on the health effects of particulate matter in the Tube. COMEAP said in 2018 that there was not enough evidence at that time to determine the health impact of underground particulate matter and that more research is needed.

We want to be certain on the nature and extent of any health risk to those travelling and working on the London Underground. That’s why TfL has also been commissioning extensive research by independent researchers to ensure that London has the most up to date and in-depth understanding of the issue as possible. The first of these studies was published in March 2024.

Dust underground vs outside air pollution

Air quality underground is different from the ambient air on the surface. Air pollutants such as nitrogen dioxide, which has been found to be harmful to humans, are common above ground but are not produced inside the Tube network.

A strong body of evidence shows the impact on health from exposure to outdoor pollution from exhaust emissions.

Travel on the Tube reduces exposure to pollutants from road traffic.

Find out what we're doing to improve London's air quality.