The Atmospheric Effects Render Element stores only atmospheric or volumetric participating media such as fog or Aerial Perspective. This render element can then be used to enhance or color-correct just the atmospheric component of the image during the compositing process.
When atmospheric effects or fog is included in a scene, they will render into the Beauty (RGB color) channel, and should also be output as the atmosphere channel for compositing use.
To use render elements, select from the Available render elements column and click the Add button to add the passes you wish to generate at render time. When you render the scene, the added render elements listed in the column on the right, will also render, which can be viewed from the VFB window's channel drop-down menu.
For more information on the parameters on this dialog, see the Render Elements tab page.
