Fog is that steam in atomasphere iscondensation by cooling near the ground so it is small drip. If it can see distance less than 1km it is fog. If it can see distance over than 1km it is mist.
The sky can see faintly that is low fog and see like coverd ground that is place fog.Fog looks white. Mix smoke or duty is called smog.

Need condition to produce fog
　　　　1 A loy of condience nucleus in air
　　　　2 Enough steam
　　　　3 cooling air
Steam alaways is helped by river,sea and ground with get wet rain.As a main result of air cooling is radioactive colling or contact with cold water or mix adiabatic expansion whit cold air.These cause mix and make fog.
And relat ionship with atomasphere stratificton condtion.

The a lot of way make mane fogs.