There is almost no smog to speak of in the SF Bay Area anymore. Certainly compared to 35 years ago. It is clean enough. There is no evidence that anyone or anything is being damaged by auto emissions in this state.
Any measures to clean it further will certainly be the final nail in the local economy's coffin.
I used to think that the brown layer you descended into dropping into Cajon Pass around 1997 was air pollution but then I realized it was simply liberal stench. Same thing really.