53% of the time, Hong Kong-based sources of pollution are to blame. Primarily cars idling in traffic, boats (which don't have to use low-sulphur fuel), and CLP's filthy power plants (which are worse than some in Shenzhen and Dongguan)
Just saying that I haven't noticed smog as a rule in other big cities. But I have never been to megacities, I am talking about London or Berlin when I say big cities.
http://www.civic-exchange.org/eng/upload/files/200703_HKAirP...