So I've done the atmosphere, but the Volume material has given it loads of dots. I assume this is the resolution of the Volume light but is there a way to get rid of them without bumping up the resolution to over 100,000?
Check out Andrew Price's article on eliminating fireflies. He lists 7 settings that reduce their appearance.
Link to Article
If that doesn't work, try adding a Despeckle node to your compositor pipeline.