"(Two hundred years ago) the only thing being emitted (in London) were horse toots."

Prager can't know much about history. The Industrial Revolution was well under way, there were factories in London, and every home, if it was warmed at all, was heated by coal-burning stoves, fireplaces, or the like. Cooking was over dirty stoves. Livestock lived in the city when the owners could afford it. Horses poooped, they didn't just pass gas. The city had a sewage system, I believe, but many people did continue throwing stuff into the street. Many factories used steam power, heated with coal ... the list goes on and on and on. I've never been surprised to hear that the air back then was putrid and thick enough to cut with a knife. I don't know why you don't know stuff like this. Maybe you should read a book or three by Dickens. Vanity Fair might give you some info. Jane Austen might give you a few pointers on how houses were managed. Probably the Bronte sisters will have some info, ya think? Fielding? Try it, you'll learn something.