I’ve lived in a couple of cities in Europe and I can tell you my nose was runny and my throat a bit rough far more often in a poluted place like London (UK) than it is in the small city I live in now in Portugal or the places I lived in when in The Netherlands.

(In fact moving to a small city in Portugal from London hugelly improved of my health when it comes to that kind of thing)

I suspect that the tendency to catch colds and suffer from alergies is often coupled with all the Sulfur Oxide gases around in cities with lots of car polution, since those turn into various sulfur oxiacids when those gases mix with water in the nose and airways.