Chattanooga is one hell of an industrial city as well. In 1969 it was the most polluted city in the US with smog worse than LA being in a bowl like shape surrounded by mountains. I-75 at the GA line has been noted for some huge wrecks by fog...
I went in May, 2010. Was almost 90 degrees but felt great at Rock City, like 15 degrees cooler...We had some thunderstorms the whole trip...
I didn't do much more than drive through on my way to New Orleans. It just looked like a nice place. It was a sunny day in the summer so I guess I missed the smog. That was about 18 years ago.