Tube commuters exposed to extreme air pollution levels

Commuters travelling on some London Underground lines breathe toxic air with levels of pollutants up to ten times higher than experienced by car drivers in the city, a new study has revealed.

The findings show that a sort of ‘environmental injustice’ is taking place as those at the highest risk of health problems due to inhaling particulate matter are not the same people who are responsible for the problem in the first place.

In the study by a team from the University of Surrey, which has been recently published in the journal Environment International, car drivers have been found to enjoy the relatively clean air inside the protective bubble of their vehicles. Paradoxically, a large portion of the particulate matter polluting air in cities is generated by diesel engines of cars, vans and buses.

Commuters relying on buses inhale air that is slightly cleaner than that taken in by tube users, the study found.

“There is an interesting trade-off of pollution exposure between different modes of transport,” said Prashant Kumar, the study's lead author.

“For example, commuters travelling to work on underground trains are exposed to the highest levels of large-sized particles while being exposed to the highest level of black carbon and ultrafine particles during commutes in buses.”

On average, the study’s participants travelling on the tube were inhaling air with concentrations of PM10, soot particles with diameter of 10 micrometres or less, of 68 micrograms per cubic metre. The drivers involved in the study averaged on only eight micrograms.

Exposure to PM was much higher on tube trains with opening windows compared to newer trains that do not have opening windows.

“The relatively new airtight trains with closed windows showed a significant difference to the levels of particles people are exposed to over time, suggesting that operators should consider this aspect during any upgrade of underground trains, along with the ways to improve ventilation in underground tunnels,” said Kumar.

Meanwhile on the surface bus users were exposed to higher levels of black carbon and particles than car users.

The researchers also found areas with the lowest incomes were exposed to the highest PM levels.

The study did not find conclusive evidence to link deprivation with higher exposure. However, people from affluent areas tended to use cars more.

Particulate matter is a serious health concern. The tiny particles escape the body’s natural defence mechanism and get deposited in the lungs, contributing to the development of respiratory conditions and increasing the risk of cancer. From the lungs, the toxic carbon and metallic particles can penetrate into the blood stream. Recently, it has been found that the particles can cross the blood-brain barrier and get deposited in the brain, where they could possibly contribute to the development of Alzheimer’s disease.

A campaign group called Doctors Against Diesel has called on the Prime Minister today to ban the most polluting diesel cars as soon as possible.

The group formed of doctors, nurses and other health workers is trying to increase awareness of the health hazards associated with polluted air.

“There is overwhelming evidence that locally generated sooty particulate matter and nitrogen dioxide is harming children's health,” said Professor Jonathan Grigg of Queen Mary University of London and founding member of Doctors Against Diesel.

“In London, we know that diesel engines are a major and unnecessary cause of air pollution along our roads. Cutting diesel emissions would therefore have an immediate impact on children's personal exposure, and improve their long-term health.”

Air pollution from sources including factories and vehicles, particularly diesel engines, is linked to the early deaths of about 40,000 people a year in the UK.

London saw legal annual limits for pollution breached on some busy roads in the first week of January.

“Diesel is the primary source of nitrogen dioxide in urban areas and is linked to health effects that begin before birth and extend throughout the life course, from childhood lung development and asthma, to increased risk of heart disease, stroke, lung cancer and dementia,” said Professor John Middleton, president of the UK Faculty of Public Health. “It is time for diesel to be recognised as the health emergency that it is.”

Figures from the Society of Motor Manufacturers and Traders show diesel vehicles continue to have a significant share of the market. Some 1.29 million new diesel cars were registered last year, representing a market share of 47.7 per cent, down from 48.5 per cent in 2015.

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