1, Baku, Azerbaijan
2. Dhaka, Bangladesh
3. Antananarivo, Madagascar
4. Port-au-Prince (pre-quake? I believe they are now uncontested #1 or will be soon.)
5. Mexico City
Most of the rest are in Africa. If I did the ranking, Mexico City would do much better than number five, since air pollution isn't as bad as the lack of sanitation in cities such as Conakry (a mere #19). And why does Bangui (CAR) get such an idyllic photo? Nor does Google offer up any nasty photos of the place.