V-Ray Volume Fog
Search keywords: simple fog, simple volumetric
V-Ray_Volume_Fog is a volumetric shader that allows the basic simulation of participating media like fog, atmospheric dust and so. However it cannot simulate the scattering of GI.
Color - defines the color of the fog when it is illuminated by light sources.
Multiplier - a multiplier for the Color parameter
Bias - this parameter allows to change the way the Color is applied; by adjusting it you can make thin parts of the volume to appear more transparent than normal, or less transparent than normal.
IOR - index of refraction for the volume. If simulating a fog inside an enclosed volume light rays entering or leaving the volume will be refracted based on this parameter