Even in the first few sentances of that article I don't understand the situation they build about who pays for what. They say auto exaust is an example of an externality since car users presumably aren't affected by its ills. Here I am thinking they certainly pay for it in terms of a tradeoff between worse local air quality and convenience. Maybe some people believe things must only be paid in cash and not through time or experience.
https://en.m.wikipedia.org/wiki/Externality