What temperature condition is necessary for ice fog to form?

Ice fog typically forms under very specific atmospheric conditions, primarily when the air temperature is below freezing. This phenomenon occurs when the temperature drops significantly, often to around -10°C or lower, and there is sufficient humidity in the air. When the air is saturated with moisture and the temperature dips below freezing, tiny ice crystals form and can remain suspended in the cold air, creating the visual effects characteristic of ice fog.

In contrast, the other temperature conditions listed would not support the formation of ice fog. Above freezing conditions typically prevent the formation of ice crystals, while being at freezing does not enable the conditions necessary to maintain airborne ice particles effectively. Lastly, temperatures of 10°C are well above the freezing point, further eliminating the possibility of ice fog forming. Thus, the requirement of temperatures being below freezing is essential for the development of this weather phenomenon.