I grew up in Los Angeles during the worst decade of pollution it ever experienced and suffered serious childhood asthma as a result. The decrease in smog after catalytic converters were invented and required in new cars was significant.

After the changes, my ability to breathe improved drastically, and I know I’m not alone. I, for one, strongly support reasonable environmental regulations as a result.

https://www.kcet.org/history-society/how-los-angeles-began-t... is a great history of those times.