Baltimore needs to clean up its act. At least that's what Travel+Leisure magazine's readers think. The magazine ranked Baltimore no. 3 on its list of America's Dirtiest Cities, based on its America's Favorite Cities survey. Last year we were no. 6. Rats. Well, actually, rats are part of the problem for many on the list, along with smog, ozone and litter, according to T+L. (They wonder if what Charm City needs is an "army of cats.") New York City came out on top of the dirty heap, followed by New Orleans. Here's a look at the Top 10 picks.