We already did...until the 1980's none of the cities we live in were visible from the air in any clarity - some of the more industrial ones never at all. A relative who was in the RAF in the sixties told me that many places they overflew were permanently covered in smog.
Until comparitively recently all Public and other major stone buildings were jet black, their Portland or similar stone had a thick coating of soot and until the Clean Air Acts started, initially in 1956, it wasn't worth cleaning them. Look at a colour film of the Coronation in 1953 and you'll see what I mean, Westminster Abbey included. Even in the 60's and 70's we got fog that stopped the traffic.
As far as emissions to atmosphere are concerned, industry is tightly controlled, with everything scrubbed clean prior to discharge, leaving vehicles as the last challenge, but even here we are doing well, with seemingly impossible (at the time of legislation) limits being met by the manufacturers