Which phenomenon involves vapor turning directly into ice?

The phenomenon that involves vapor turning directly into ice is known as frozen dew. This occurs when water vapor in the air undergoes deposition, a process where water vapor changes directly from a gas to a solid without first becoming liquid. This typically happens under specific conditions where the temperature drops below freezing, allowing the moisture in the air to crystallize and form frost.

In contrast, dew is the result of moisture condensing from the air to form liquid water droplets on surfaces as temperatures drop at night. Fog and haze involve the presence of tiny water droplets or ice crystals suspended in the air, but they do not specifically refer to the process of vapor turning directly into solid ice. Therefore, frozen dew is the correct term that describes this specific transition from vapor to ice.