WordNet (r) 3.0 (2006):

air pollution
    n 1: pollution of the atmosphere; "air pollution reduced the
         visibility"

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "air pollution":
   air, attritus, badness, bran, contamination, cosmic dust, crumb,
   crumble, dust, dust ball, efflorescence, fallout, farina, filings,
   flour, grits, groats, harmfulness, health hazard, injuriousness,
   insalubriousness, insalubrity, kittens, lint, meal,
   menace to health, noise pollution, noisomeness, noxiousness,
   pathenogenicity, pollution, powder, pussies, raspings, sawdust,
   smut, soot, unhealthfulness, unhealthiness, unsalutariness,
   unwholesomeness, water