Dirty? What parts of Atlanta? One of my favorite things about Atlanta is how green it is. After living on the west coast for awhile it felt amazing to come back and actually see something green.
Dirty is probably the wrong word... maybe run down? Roads are in poor condition, abandoned warehouses/factories everywhere, it looks like people don't care about the area. Probably nearby the airport, because that's where I fly in and drive out from there. But even inside the city, it doesn't look much better... I still get that same feeling.
ATL is green, has lots of trees, it's beautiful, but the trash on the side of the roads is ridiculous (I'm talking 285, 400, 75, 85) and seems to be getting worse. It's especially bad around the airport; so much for first impressions. If you go outside of ATL (or even inside) the situation improves a lot.
Well yeah, in and around the airport is a pretty horrible area but that seems like an odd way of judging a city. As for the highways I can't really say it is any worse than any other city I have been to.
We all have our standards. If I come to your house and there's trash on the lawn I won't leave with a good impression. For me that shows lack of management / organization. It's not like they can't afford it.
I can see piles of trash left from former homeless encampments on the side of the highway from my downtown Seattle office, so I guess Seattle is a shitty city too.
Doesn't make the entire city shitty, but it's not excusable either. There are much poorer cities (in relative poor countries) that don't have that problem. Also, the fact that you're defensive about this gives us a clue as to why the problem persists.