Technically to limit noise pollution to those who walk into a club is the easiest of all, you just turn down the music.
That would suit me fine most of the time. But more seriously, it could well be easier to limit smoke pollution through adequate ventilation however I don't know about the effects of the carginogens, do they hang around in the air or do they just get sucked away with the smell? I'd assume the latter but I couldn't say for definite.
I don't think I've seen anyone wearing earplugs in a club either although I have at gigs where people have worn them, some of the more advanced ones filter sound so that normal conversation can still be attempted I believe. I dunno about the dust masks and how effective they are/were but that was the rave scene? Before my time going out really and it is difficult to claim too much concern for your health when popping pills (or drinking come to that).
It is possible although I think a bit unlikely, however that was probably said about the smoking ban as well.
//edit Lysander - the problem is the freedom of choice argument cuts both ways, if you want to go into a club to enjoy loud music then some other people will want to go in so they can smoke(and enjoy the loud music).