How much are sunshine hours influenced by pollution in smoggy cities (in Asia etc.), compared to "real" values? (climate, averages)

[markovian process]

Reading this article made me think about the question.

The Desolation of Smog - An FP Slideshow | Foreign Policy

I saw on this forum and on stats for east Asian cities on Wikipedia that consistently they are very cloudy, much more than similar climates in the United States. Sunshine hours are very low, in the 1000s. Is it possible that there has been a very strong underestimate based on what smog there is there, like England during its more industrial times?

More broadly, how much does this influence cities across the world as a whole? Would sunshine hours have been much different at various world cities' current locations, in a world without industrial activity of people?

[ben86]

One of the longest (the longest?) set of continuous sunshine data for England is from Bradford, which conveniently used to suffer from horrendous pollution until a few decades ago. It's a very dull city anyway, with a 1981-2010 average of 1265 hours, but while I've never taken the effort to work out old 30-year averages from the dataset here, I have added up the monthly figures for 1912 and got just 816 sunshine hours, whereas I would be surprised if any year in modern times has gone much below 1100.

Having a look at how often sub-20 and sub-10 hour months happened during the 1910s and 1920s compared to today, I can imagine the pollution having taken up to 50% off the long-term average 'natural' amount of winter sunshine the area would have got otherwise. I'd also be interested to know what London's December 1890 with zero sunshine would have been if not for pollution, as anything below 30 hours counts as very dull down there nowadays.