The best air in India is from Kerala, yet it's as bad as smoking one cigarette

After Bryan Johnson left the WTF podcast, Nikhil Kamath took over as the host. He mentioned that he can’t manage the 110 AQI air because he is coming from a place with an AQI of 10. I thought our kerala air was the best because we don’t have many industries. However, in Europe and the US, the air quality index is often below 20 or 50, while we don’t have any city with an index below 50. What is the main factor behind this, even though we don’t have many industries?