> Anecdotal, however, I used to work with meteorologists and they would always live to the West of the city centre, to get cleaner air than those living in the east of the city, or further downwind.

The industrial-revolution era mill owners were very aware of this too. Posh area of Manchester is to the south (westerly winds;) Leeds to the north (mix of northerly and westerly winds I believe).

Also, anecdotally, smaller towns and villages can have poor air quality too due to log burners. They're an absolute pain. You can tell when an area has become gentrified when shiny new chimneys start popping up or a log burner shop opens up!