Specifically: Leaded gasoline (with tetraethyllead), nitrogen oxides (NOx), sulfur oxides (SOx), carbon monoxide (CO), unburned hydrocarbons.

https://en.wikipedia.org/wiki/Tetraethyllead , https://en.wikipedia.org/wiki/Sulfur_oxide , https://en.wikipedia.org/wiki/NOx

Only in developed countries. The age of a typical car in my region is over 15 years. Basically, most of what you bought in 2005-2010, drove for a decade or more, and then sold for scrap eventually ends up in countries like mine. Moreover, most people take catalytic converters off their cars and sell them for $80-100 for platinum recycling.

I think most "developing" countries have the same problem. So the world at large hasn't really solved it and won't solve it any time soon.