The BBC programme 'More or Less', Friday afternoons at 4.30 (I'm driving home from work this time), covered this topic recently. A listener had asked if it could really be true that pollution in London caused 40,000 deaths per year and Greenpeace's assertion that living in London was equivalent to smoking 15 cigarettes every day? The programme consulted a professor of respiratory medicine from one of the big London hospitals and his reply was illuminating.
The 40,000 figure was the result of a statistical study(ies) which properly interpreted pointed to those people dying in old age and having their lives shortened by some months by pollution - not quite what the assertion brings to mind immediately. As for the Greenpees comment - 'nonsense' he said.
'Yeeesss' I thought, like everything they say.