London has long been known as the pollution capital of the UK, incurring fines from the EU over its poor air quality for several years running. But how does its primary mode of public transport compare to the outdoor air pollution?

As the preferred transport method for up to five million journeys every single day, the ramifications of the Tube’s air quality (or lack of it) could be far-reaching for many people. A new study from King’s College London has found that those ramifications could be dire indeed, with the Tube experiencing worse levels of air pollution than anywhere else in the UK capital.

The Big (underground) Smoke

Financed by the Mayor’s Air Quality Fund, the study monitored the commuting routes of eight London professionals over a two-week period. During the first week, the subjects wore continuous emissions monitoring equipment (CEMS, which are enjoying increased popularity of late, even in the developing world) on their normal route to work. For the second week, they made slight alterations to their journey to see if it made a difference to their exposure to air pollution.

The results were staggering. Some subjects experienced a discrepancy of 89% in the amount of pollution they were exposed to, simply by ditching the underground in favour of overground trains. What’s more, those who used deeper underground lines (such as Victoria and Northern) recorded even higher levels of contamination than those on higher lines.

The study concentrated solely on the Northbank area of London (from Aldwych to Trafalgar Square), but still represents the most comprehensive investigation into air pollution exposure for visitors and commuters in the British capital to date.

Small changes, big differences

As well as favouring overground trains rather than the underground, the study also found that slight alterations to walking or cycling routes above ground could pay massive dividends. Those who chose a less polluted route to their station of choice (via the district’s Clean Air Route Finder) saw their exposure to contaminants fall by as much as 50% from one week to the next.

The populace of the city (and the country in general) is becoming more preoccupied with pollution levels, as evidenced by the impressive growth at this year's Air Quality and Emissions Event. In response, Mayor Sadiq Khan has vowed to implement a number of measures designed to improve air quality levels across the city, including expediting the introduction of ultra-low emissions zones (ULEZs), replacing speed bumps with speed humps and optimising traffic light coordination to encourage smooth driving.

What’s more, the C40 Air Quality Network (of around 20 cities across the world) recently announced it will create the most sophisticated air monitoring system known to man in the UK capital in the near future. With a budget of £750,000, the project is currently accepting proposals on how best to implement the new system.