One thing everyone seems to be forgetting is that HOW the pollution is measured is a HUGE factor as to which cities will make the list and which wont. If you do your research you find all kinds of lists from various colleges and institutions with completely different cities on them which claim to be the most polluted. Some look at ozone, some measure ground and water pollutants, some measure particles in the air, some our own carbon footprint, and some a combination of any one of those! With all of these variables, it is easy for any major city to be on a list at some point. The question is, which list holds the most merit?