Delhi in India has the highest levels of air pollution on the planet but only now are the locals being made aware of it. Daily, its inhabitants breath in air that is so toxic that it can lead to death or serious diseases. We may think London, on a bad day, has problems but these are insignificant when compared with Delhi.
I have heard that pollution is also bad in China.
See http://www.bbc.co.uk/news/magazine-32352722 .