I think you grossly underestimate the degree to which cars (and industry that we had yet to kick out to China) were dirtier decades ago than they are today.
We're talking like literal orders, plural, of magnitude when comparing between the generally no cats automotive fleet of the 70s with anything since the advent of both cats and computerized fuel injection. Any old timer can tell you of the smog that used to be frequent in urban areas. These days it's mostly gone, at least when California or Canada (depending on where you live) isn't on fire.
(INB4 people who are a net negative to public discourse construe this comment as some sort of endorsement for everyone driving everywhere all the time)
Just look at old photos of city smog in the 1960s. It is night and day different compared to air today even with larger populations in these same metros in some cases.
We're talking like literal orders, plural, of magnitude when comparing between the generally no cats automotive fleet of the 70s with anything since the advent of both cats and computerized fuel injection. Any old timer can tell you of the smog that used to be frequent in urban areas. These days it's mostly gone, at least when California or Canada (depending on where you live) isn't on fire.
(INB4 people who are a net negative to public discourse construe this comment as some sort of endorsement for everyone driving everywhere all the time)