When you apply a volume shader to a render pass, it surrounds the scene rather than being bound to a single object.
To create a volumic scene effect
Select the pass to which you will apply the volume shader and open its Render Pass Property Editor.
In the Volume stack window, click Add to select a volume shader from the shader library. See Volume [Shader Reference].
Click OK when you have chosen a volume shader — it appears in the shader stack list.
Select the shader in the Volume stack window and click Inspect. This opens the shader's property editor.
For more information on how to use a particular volume shader, click the help icon in the shader's property editor.
