A mix of experimenting with the Volume for the smoke effect and also applying so lights (glow). The majority I found where quite successful in regards to leading me to my final destination.
2 & 3 may be hard to see but here Im playing with the brightness of the glow to try and control its effect.
Here Ive taken away the background of the hills to see what effect it would give. It massively increased the darkness and loses its atmosphere.
10 & 11 are experimenting with a bubble kind of texture. This looks a little to spotty for me.
Here im begining to explore the colours of the hills to see if a different colour would work more with the atmosphere if it had some more tone.
I continued to explore adding a gradient to both the smoke and the hill to get a more tonal feel. I felt this was quite successful and with a little more refinement should work well.