When visiting India ~15 years ago, even mid-sized (for India, so ~1m people) cities were so polluted that the air was yellow. This was despite the fact that far

When visiting India ~15 years ago, even mid-sized (for India, so ~1m people) cities were so polluted that the air was yellow. This was despite the fact that far fewer Indians own a car per capita than in the west- but the car they did own (and/or fuel they used) were horribly polluting.