I’ll cover how I enhanced the atmosphere.
When I rendered my image, I also rendered a depth pass and a volume primitive pass. The volume primitive pass was rendered to add the dynamic hair to the depth pass, which was covered previously.
I took the raw background layer, select all, and copied and pasted a couple times (I like extra layers to play around with). One of the background layers I just created I turned into a Layer Mask. I clicked on Channels tab, selected the Depth Pass which PS calls Distance, and copied it.
I went back to the Layers Tab, and option clicked the layer mask, and pasted in the depth pass. I created a new layer and used a color gradient to fill it. I placed it under the layer mask. I saw that I needed to invert the layer mask.