This page describes the V-Ray Simple Fog feature.
Overview
VRaySimpleFog is an atmospheric effect that simulates participating media like fog, atmospheric dust and so forth. However, it cannot simulate the scattering of GI and no maps can be used.
UI Path: ||Hypershade|| > Create panel > VRay section > Volumetric > VRay Simple Fog
Parameters
Emission – Controls the fog emission (self-illumination). This parameter is used to substitute the ambient illumination inside the fog, instead of using GI.
Color – Defines the color of the fog when it is illuminated by light sources.
Color multiplier – A multiplier for the Color parameter.
IOR – Index of refraction for the volume. If simulating a fog inside an enclosed volume light rays entering or leaving the volume is refracted based on this parameter.
Bias – This parameter allows to change the way the Color is applied. By adjusting it you can make thin parts of the volume appear more transparent than normal, or less transparent than normal.