A typical commute to work on the London Underground exposes commuters to the same amount of air pollution as a day on the roads, according to a new report.
The report, by the Committee on the Medical Effects of Air Pollutants is however laden with caveats, and the conclusions to be drawn from it somewhat inconclusive, due to the small sample sizes and limited time of research.
A headline summary is that one hour on the tube is equivalent to a day on the streets, in so far as exposure to air pollution is concerned.
One key issue is that the report, which is based on other studies is fixed in location – at Hampstead station, and it’s unlikely that the average commuter will spend more than a few minutes waiting on the platform. Particle exposure inside the trains, was not included in the report.
Hampstead station was chosen as being the deepest on the network it was less likely to have readings on the platforms affected by surface pollution being drawn down into the tunnels by ventilation systems.
The report focuses on the effects of fine particulate matter (PM2.5) because it is a concern for people’s health when levels in the air are high. Their very tiny size makes it easy for them to get into the lungs, but rather harder to get back out again.
People with breathing and heart problems, children and the elderly may be particularly sensitive to PM2.5. However, the age profile of users on the Underground suggests fewer children and elderly use it, so the overall impact on health of London as a whole may be less than the headline suggests it would be.
Routine monitoring in the London Underground by TfL over many years has shown that concentrations of total inhalable and respirable dust to which train operators and station staff are exposed in a daily shift are all significantly lower than workplace exposure limits.
That’s not to say they are necessarily good, but that given the choice between a job in a dirty factory or the London Underground, the tube would be less bad for workers health.
The report notes that health based studies have been carried out on other underground networks, but not London’s, so the specific differences with London to others are currently unclear.
Where studies have directly compared the effects of underground PM to particles from other modes of transportation, there is evidence that, in human lung cells, underground PM exhibits more potent inflammatory effects than tyre and road wear particles and negative control particles (eg carbon black and titanium dioxide). However, there is generally, but not always, a higher pro-inflammatory potential of ambient particles collected in urban settings compared to those collected underground. In contrast to the inflammatory response, underground train particulates have generally been reported to induce greater oxidative stress than an equal mass of urban airborne particles.
The main conclusion from the study is that due to the limited amount of heath impact data available, that more studies are needed, but also that TfL should take steps to reduce particulate exposure where possible anyway.
Fortunately though, here has been a reduction in air pollution in the tube network in the past couple of years.
During the summer of 2017, nearly 50 stations and five tunnel sections were cleaned with industrial vacuums and “magnetic wands”. However, it is currently unknown if, and how quickly, dust concentrations return toward baseline levels after cessation of the cleaning, so TfL is currently testing this on another section of the network.
Certainly as the headline level, higher exposures in the tube network are not a good thing, but equally, we spend so little time in those environments that other issues may be a greater problem. Working in an office tends to expose people to higher levels of air pollution than being outdoors, and don’t even think about the state of air pollution in your home when cooking your supper using a gas hob.
The full report is here.