While I agree air pollution is worth considering, "very bad" sounds like hyperbole to me. Definitely not anywhere near smoking. The solutions also are rather simple: change your route to avoid heavy traffic and/or wear an air filter. I've done both before and recommend the latter more, as it seems more effective, does not make breathing harder, and has other safety benefits as well. Also consider the length of one's commute.

It's also worth noting that air pollution can easily be worse when driving. In fact, while I can not find the link now, I recall one non-scientific article with some experiments run by academics suggested that net exposure to air pollution was higher when driving in some cases.