So there are (at least) two issues here, right?
1) Boundary of the volume grid visible directly or in alpha
2) Jagged edges where the mountains meet the sky
As to 1, the solution could be:
- Disabling "single bounce only" option for the global volume material and / or for the volume grid. I had a similar issue recently, and this solved it (in my case, disabling it for the global fog).
- Adjusting the distance of the sky environment. This can be done by accessing the "development / experimental stuff" rollout (
https://coronarenderer.freshdesk.com/support/solutions/articles/12000021288) and then adjusting "enviro distance". Unfortunately I can't tell you if it should be set to higher or lower. :) You would need to experiment with it.
As to 2:
- It looks like DOF. Are you sure that you have DOF disabled in your current camera / perspective view?