It seems that many feel that exercising when there is a lot of air pollution is a bad idea but I haven't seen any articles specifically measuring these effects on bicycle commuters. The air is generally pretty good here in Hawaii but Kilauea has been acting up lately and we are getting a lot of vog. Just doesn't seem to bother me when others are complaining. The worst air I get are from the stupid 2 cycle mopeds (although school buses are a close second). I'm starting to see a few electric mopeds and they are so quiet and clean I wish they would catch on.