You can have Atmospherics and Render Effects
assigned per pass. This is accomplished by RPM controlling the Enabled
state of the atmospherics and render effects in the scene on a per
pass basis, rather than creating and deleting items.
The basic steps are to create all the atmospherics
and render effects you need for the scene, and then enable or disable
them for each pass as needed using the Atmospherics or Render Effects
rollouts in the RPM interface.