[rdouble]

That's because the NYC summer is hot

That's true, but it's still a dirty city. However, it's a different type of dirty than SF. The dirty parts of SF are dirty due to insanity and apathy. NYC is dirty because there are so many people out and about, all the time.

[elblanco]

I've noticed this as well. NYC is grimy and can get dirty, but it's not the kind of unsanitary filth that you might find in a sewer. As such, I don't mind walking about all day and getting a bit sooty, at least I won't catch something from it.