Why is there fog?

When the relative humidity reaches 100%, the water vapor in the air will condense into fine water droplets suspended in the air, which will reduce the visibility on the ground. This weather phenomenon is called fog.

Second, the definition:

Fog is a weather phenomenon composed of tiny water droplets or ice crystals suspended in the air near the ground, and it is the product of condensation (or sublimation) of water vapor in the air near the ground. It is a liquid.

Third, the formation conditions:

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

Fog is formed by radiation cooling, which often occurs at night and early morning when the sun is shining, the breeze is blowing gently, the water vapor near the ground is rich and stable, or there is inversion. Meteorology calls it radiation fog.

The other is that warm and humid air moves horizontally, passing through the cold ground or water surface, and the water vapor in the air is gradually liquefied by cold to form fog, which is called advection fog in meteorology.

Sometimes the fog formed by two reasons is called mixed fog. It can be seen that it is late autumn and early winter that can meet these conditions, especially in the morning of late autumn and early winter.

The smog in the city is caused by another reason, and that is human activities. Morning and evening are the peak hours of heating boilers. Under the condition of low air pressure and low wind speed, a large number of pollutants, such as smoke, suspended solids and automobile exhaust, are difficult to diffuse, and it is easier to form smoke (fog) when combined with water vapor in the lower air, and this smoke (fog) often lasts for a long time.

Extended data

Hazards of fog:

(1), which may cause changes in insulators of transmission lines and outdoor electrical equipment, even lead to accidents and endanger human health. ?

(2), affect visibility, easy to cause traffic accidents.

(3) Now scientists believe that fog is caused by the existence of "inversion layer", the atmosphere is very stable, convection is weakened, and pollutants such as water vapor and dust in the air are not easy to spread to the sky and can only stay near the ground. When the fog drops dissipate, all pollutants will enter the air, causing serious pollution and directly endangering human health. ?

(4) According to the determination of scientists, the proportion of various harmful substances such as acid, alkali, salt, amine, phenol, dust and pathogenic microorganisms. The concentration in fog drops is dozens of times higher than that in atmospheric water drops. The harm of this pollutant to human body is most obvious in the respiratory tract.

Anti-fog measures:

(1), try not to go out, and wear a mask when you have to go out to prevent inhalation of toxic gases. ?

(2), as little as possible in foggy days, don't exercise in foggy days.

(3), pedestrians should be careful when crossing the road, should see the traffic. ?

(4) Drive vehicles and cars slowly, obey the traffic police's command, and don't rob the bus (boat). The ferry has stopped. Don't crowd at the ferry.

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