How is fog formed? A simple answer

Excess water vapor in the air meets tiny floating particles and sticks to each other, forming small ice crystals and water droplets, which are the fog we usually see.

The excess of water vapor in the air is mainly caused by the sudden drop in temperature, so foggy weather often occurs in the mornings of autumn and winter.

When the relative humidity reaches 100% when there is sufficient water vapor, a gentle breeze, and the atmosphere is stable, the water vapor in the air will condense into fine water droplets suspended in the air, reducing visibility at the ground level. This The weather phenomenon is called fog. It mostly appears between February and April in spring. Conditions for formation: First, cooling, second, humidification to increase water vapor content.

Cause

When the air holds the maximum amount of water vapor, it reaches saturation. The higher the temperature of the air, the more water vapor the air can hold. When the temperature is 4°C, 1 cubic meter of air can hold up to 6.36 grams of water vapor; when the temperature is 20°C, the maximum amount of water vapor that can be contained in 1 cubic meter of air is 17.30 grams. If the air contains more water vapor than the saturated amount of water vapor at a certain temperature, the excess water vapor will condense out. When enough water molecules combine with the tiny dust particles in the air, the water molecules themselves will also interact with each other. When bonded, they become small water droplets or ice crystals. The water vapor in the air exceeds the saturation level and condenses into water droplets. This is mainly caused by the drop in temperature. This is also the reason why mornings in autumn and winter are foggy.

If the ground loses heat, the temperature drops, and the air is quite humid, then when it cools to a certain level, part of the water vapor in the air will condense out and turn into many small water droplets suspended near the ground. In the air layer, fog is formed. Both it and clouds are caused by a drop in temperature, and fog can actually be said to be clouds close to the ground.

The temperature is relatively high during the day and the air can hold more water vapor. But at night, the temperature drops, reducing the air's ability to hold water vapor. Therefore, some of the water vapor condenses into fog. Especially in autumn and winter, because the nights are long and there are more opportunities for cloudless winds, the ground dissipates heat more quickly than in summer, causing the ground temperature to drop sharply. This makes the water vapor in the air near the ground easy to evaporate from late night to morning. It reaches saturation and condenses into small water droplets, forming fog. The early morning temperatures in autumn, winter and spring are the lowest, which is when the fog is thickest.

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