Hacker News Reader

For people living in the US like me, this is where you find US pollution maps: https://usa.maps.luftdaten.info/

Holy cow, that must be a German project; Germany has nearly 100% coverage, the USA has almost none.

I was expecting China and India to be dark purple

If you want a more international / american version, check out purple air: https://www2.purpleair.com/

Is purple air the proprietary version?

No it's another independent community effort, go read it's about page.