I don't know what to tell you if you say that you bike around the crowded city streets of Seattle and you have never smelled vehicle exhaust. I in particular do not have a very keen sense of smell and hardly a minute goes by without having to hold my breath to wait for a plum of fumes to disseminate. Yes, I would agree that the plumes are not visible, but that is not what I'm claiming. Just because they are not visible does not mean they are not affecting our health.