According to a new study commissioned by Transport for London, the air in parts of the city’s subway system is thick with harmful particulates, with some of London’s Tube stations registering levels of air up to 30 times worse than the average for a London street above ground.

In the worst cases of underground pollution, it’s possible that particulate pollution of this type is a feature of subway systems across the world. The study nonetheless makes two things clear. First, that London Underground’s particulate problem is notably worse than other city systems thanks to the network’s age and design. Second, that despite increasing awareness of the noxious effects of motor vehicle exhaust fumes, many harmful particulate emissions on the network do not come directly from fuel combustion.

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