What if we made HEPA filters in cars mandatory in such a way that every car ‘clears out’ the smog it creates plus some extra (won’t help for all the coal burnin

What if we made HEPA filters in cars mandatory in such a way that every car ‘clears out’ the smog it creates plus some extra (won’t help for all the coal burning). We could then throw out/recycle the filters once in a while and at least compensate for traffic related smog.