What is the origin of fog and how is it formed?

fog (wù) has three definitions:

1. When the visibility in the atmosphere is less than 1 km due to the condensation of suspended water vapor, meteorology calls this weather phenomenon fog.

2. Fog is a cloud that is close to the ground.

3. Fog is an aerosol composed of tiny droplets suspended in the atmosphere. (described in Environmental Monitoring).

Saturation is achieved when the water vapor contained in the air reaches its maximum. And the higher the temperature, the more water vapor can be contained in the air. 1 cubic meter of air, when the air temperature is 4, the maximum amount of water vapor that can be contained is grams; When the air temperature is 20, the maximum amount of water vapor that can be contained in 1 cubic meter of air is grams.

If the air contains more water vapor than the amount of saturated water vapor at a certain temperature, the excess water vapor will condense and when enough water molecules combine with the tiny dust particles in the air, and the water molecules themselves will bond to each other, becoming small water droplets or ice crystals. The amount of water vapor in the air exceeds the saturation amount and condenses into water droplets, which is mainly caused by the drop in air temperature. This is also the reason why autumn and winter mornings are foggy.

1] If the heat of the ground is lost, the temperature drops, and the air is quite humid, then when it cools to a certain extent, a part of the water vapor in the air will condense and become many small water droplets, suspended in the air layer near the ground, and fog will be formed. Both it and clouds are caused by a drop in temperature, and fog can actually also 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, and the ability of the air to hold water vapor decreases, so some of the water vapor condenses into fog. Especially in autumn and winter, due to the long nights and the chance of cloudless wind, the ground heat dissipation is more rapid than in summer, so that the ground temperature drops sharply, so that the water vapor in the air near the ground is easy to reach saturation in the second half of the night to the morning and condense into small water droplets, forming fog.

In autumn and winter, the morning temperature is the lowest, and the fog is at its thickest.

A suspension consisting of a large number of tiny water droplets (or ice crystals) in a layer of air close to the ground. When fog occurs, horizontal visibility is significantly reduced. Generally, fog with a horizontal visibility distance of less than 1,000 meters is called fog; The fog that can be seen at a distance of 1,000 meters to 10,000 meters is called light fog.

The water droplets in the fog are called fog droplets, and their radius is mostly 2 15 microns. The sum of the water volume of fog droplets in the unit volume of air is called the water content, the water content in the fog is generally gram cubic meters, and the fog with a temperature higher than 0 is called warm fog; A drop below 0 but still consisting of droplets is called a cold mist; When the temperature is extremely low, the water vapor directly condenses into ice crystals, which is called ice fog.

The conditions for the formation of fog are cooling, humidification, and condensation nuclei to increase the water vapor content.

A kind of fog is formed by radiative cooling, and most of them appear at night and early in the morning when it is clear, breezy, and the water vapor near the ground is relatively abundant and stable, or there is a temperature inversion, and it is called radiation fog in meteorology.

The other is the horizontal movement of warm and moist air, passing through the cold ground or water surface, and the water vapor in the air is gradually liquefied by the cold and forms a fog, which is called advection fog in meteorology.

Sometimes fog formed by both causes is called mixed fog. It can be seen that these conditions can be met in late autumn and early winter, especially in the morning of late autumn and early winter.

Smog in cities is caused by another cause, and that is human activity. Morning and evening are the peak period of heating boilers, and a large number of pollutants such as smoke and dust suspended solids and automobile exhaust are not easy to diffuse under the conditions of low air pressure and low wind, and combine with the water vapor in the low-level air, which is relatively easy to form smoke (fog), and this smoke (fog) often lasts for a long time.

Both fog and clouds are caused by a drop in temperature, and fog can actually also be said to be clouds close to the ground. During the day, the temperature is relatively high, and the air can hold more water vapor. But at night, the temperature drops, and the ability of the air to hold water vapor decreases.

As a result, some of the water vapor condenses into fog. Especially in autumn and winter, due to the long nights, the ground heat dissipates more quickly than in summer, so that the ground temperature drops sharply, so that the water vapor in the air near the ground is easy to reach saturation in the second half of the night to the morning and condense into small water droplets, forming fog. Autumn and winter are the morning when the temperature is the lowest, and the fog is the thickest.

Causes of the formation of fog:

When there is sufficient moisture, light breeze and stable atmosphere; When the relative humidity reaches 100%, the water vapor in the air condenses into tiny water droplets suspended in the air, which reduces visibility at ground level, a weather phenomenon known as fog.

Conditions for the formation of fog: cooling; humidification; Increase water vapor content.

Types of fog: The comic wheel has a radiant fog; advection fog; mixed fog; Evaporative mist.

Foggy season: autumn and winter.

Reason: Because the night is long, scattered and there is more chance of cloudless wind, the ground heat dissipation is more rapid than in summer, so that the ground temperature drops sharply, so that the water vapor in the air near the ground is more likely to reach saturation in the second half of the night to the morning and condense into small water droplets, forming fog.

1. Under the condition of sufficient water vapor, breeze and atmospheric stability, when the relative humidity reaches 100%, the water vapor in the air will condense into fine liquid nano water droplets suspended in the air, which will reduce the visibility at the ground level. Grip.

2. Fog is formed by the condensation of water molecules in the air at night, and is generally formed in the morning of spring, autumn and winter.

3. The temperature of water vapor in the air is high, and when it encounters the air with lower temperature, small water droplets are formed, that is, fog is formed; After a period of time, the small water droplets absorb the heat in the air and vaporize, turning into water vapor and dissipating in the air.

Fog is formed by the cooling of water vapor.

The formation of fog requires three conditions: first, cooling, when the water vapor in the air is sufficient, the breeze is just right, the atmosphere is stable, and the temperature near the ground drops, the water vapor is cooled to form fog; The second is humidification. The formation of fog requires a relative humidity of 100%, and when the humidity does not reach the standard, the water vapor content needs to be increased until the humidity reaches the standard. Finally, there must be a condensation nucleus.

In the presence of both humidity and cooling conditions, condensation nuclei need to form for fogging to occur.

1. Cooling, which is the main condition for the formation of fog. When the air is well hydrated and the humidity reaches 100 percent, cooling is key. Because if there is no cooling and cooling water vapor, then it is difficult for water vapor to condense, which makes it difficult for fog to appear.

Second, humidity, humidity is a necessary condition for the formation of fog, but also a raw material of fog, if there is not enough humidity, enough water vapor, then, fog is impossible to form. Under normal circumstances, the humidity of this water vapor should reach saturation, otherwise even if it is cooled and cooled, it will be difficult to form fog due to insufficient water vapor.

Third, condensation nuclei, water vapor conditions, cooling conditions, this time to see whether it can be condensed, only the formation of small water droplets or ice crystals, fog will form. Of course, the most important thing here is to have cooling and cooling, the water vapor is sufficient, and after cooling and cooling, general condensation nuclei appear.