"were" ?
Unless you live in the country side it _is_ an immediate problem to your health and a time bomb for the planet.
https://www.who.int/airpollution/en/
> mostly solved in developed nations
That's exactly the type of thinking that will destroy us. It's always China, or Russia, or developing countries, or your neighbours, or the damn democrats/republicans. Nobody wants to take responsibility. Let's continue to act like 8 years old while our home is slowly burning.