My thought: a common meme is that lax auto emission regulations hurt the poor the most. Actually, the bigger effect on the poor is that strict emission standards largely make cars unaffordable for the poor. I suspect they then become pedestrians or bicyclers, getting struck and killed by automobiles in numbers that dwarf the number dying from lower air quality.
http://m.phys.org/news/2015-10-analysis-...ution.html
http://m.phys.org/news/2015-10-analysis-...ution.html