I don’t have any sources, just another anecdote. I live in Beijing, and one of my friends gets a headache whenever the air gets close to 200 AQI. (That’s not th

I don’t have any sources, just another anecdote. I live in Beijing, and one of my friends gets a headache whenever the air gets close to 200 AQI. (That’s not the case for me or most people I know though. Me, I get a days-long sore throat once a quarter unless I have an air purifier at home and at work) Why not buy an air purifier?