Pollution Study in Commuters, Test subjects required

the majority of vehicles I see on my commute are buses and taxis. The pollution is easily visible
at night when the cars have their headlights on.

I use the figures produced by London Mayor, to highlight the link between black cabs and air pollution, because cabs are responsible for nearly a third of particulate pollution in central London.

http://www.mayorwatch.co.uk/black-cabs-and-pollution/201116767