During a road bicycle race, like Giro d'Italia or Tour de France, cyclists have to share the road with the support cars and often ride just behind them. Don’t they mind the exhausts from the cars, or do the exhausts inconvenience them? Do the cars have any special equipment to reduce the harmfulness of their exhausts (or, at least, is there regulation requiring the cars to fulfill some stricter norms)?
Having ridden in traffic, on 6 lanes roads, even on highways (with shoulders) I can say the exhaust is a non-issue. Considering how few support cars there actually are, compared to a 6 lane road, I would say it is not even noticeable.