Lend it to a smoker for a few years.
As a previously heavy smoker I can vouch for the film that forms on window glass and anything else in the room.
To lend some credence to this notion, bear in mind the atmosphere in times past, especially in cities, was generally more heavily contaminated than we're used to now. Indoors; smokers, open fires, stoves, ranges, the general fug of living without adequate ventilation. Outdoors; plenty of smog, soots, industrial air pollution of many types.