I wish the press wouldn’t conflate clean air with climate change which are quite separate problems even though sometimes they have common solutions (and sometimes not - early attempts at emission control decreased fuel economy).
In a theoretical sense, I agree that CO2 emissions from cars (which is exactly determined by the MPG so I wish we could just stay with that measure) is a natural problem to manage federally. CO2 at even 1 part per thousand (by the time we get there maybe conservatives will agree there’s a problem) is not a local human health issue, but it is a world climate issue. So it makes sense to have a federal (but aggressive) standard.
However, with the density of cars we have in California cities (I’m in LA) and the mix of old and new cars, we definitely have health problems related to air pollution (HC, NOx, particulates, CO) from cars and it should be our right to attempt to address this issue the best we can.
This is another reason we need to get rid of the Electoral College. Trump doesn’t give a crap about CA since he can never win our state and likely no Republican ever will again. Thus any disgruntled rich Trump voters or poor white uneducated voters or any other Trump voters who still have to breathe the lousy air here - well fuck them I guess.