CO has strict emission rules. It's a problem here because of our altitude and population density. Until they started cracking down we had a brown haze constantly in the air.
How long ago was the crackdown? Because I feel like things are noticeably better than normal this year re: the haze. I mean, it could be because temps seem to be lower than usual and we've had more rain and no major wildfires. But it could also absolutely be that some long-term programs are having an impact.
CO has strict emission rules. It's a problem here because of our altitude and population density. Until they started cracking down we had a brown haze constantly in the air.
Same with CA, obviously, but in CA, the ONLY thing they care about is emissions. Your car could be held together with rubberbands, but as long as it passes the smog check, you're good for another 2 years!
I will say that my husband lived in LA for the first time from 1996-2001 and when he moved back in 2008 he said the smog issue was noticeably better. More traffic, actually, but better air quality.