Question: What is polluting the air most?

Oliver Gordon answered on 6 Mar 2019:

This is not something I know, but would really like to. It’s hard to say what “the most” is – by weight or by impact to the planet? Then there’s also things such as light pollution, which stops astronomers from seeing the stars.

I did some googling – it seems to vary from place to place. That makes sense – in cities where there’s lots of people, it’s largely CO2 and sulphur from cars, fuel burning, etc, but in less populated, tropical areas it can be ash from volcanoes.