'People should be alarmed': air pollution in US subway systems stuns researchers

Riders in major cities, especially New York, encounter particle quantities well above safe levels

People traveling on subway systems in major US cities are being exposed to unsafe amounts of air pollution, with commuters in New York and New Jersey subjected to the highest levels of pollution, research has found.

Tiny airborne particles, probably thrown up by train brakes or the friction between train wheels and rails, are rife in the 71 underground stations sampled by researchers during morning and evening rush hours in Boston, New York City, Philadelphia and Washington DC, the cities that contain the bulk of subway systems in the US.