What is fog? Causes and types of fog.

The conditions of fog formation are cooling, humidification and condensation to increase water vapor content. A kind of fog is formed by radiation cooling, which mostly appears at night and early morning, when the weather is clear, the breeze is light, the water vapor near the ground is rich and stable, or there is inversion. Meteorology is called 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. For example, London, known as the "foggy city" (note: there is no serious smog in London now).

The fog dissipates because, firstly, the fog drops evaporate due to the warming of the underlying surface; Second, the increase of wind speed will blow the fog away or lift it into clouds; Then turbulent mixing, water vapor upload, heat transfer, and evaporation of droplets near the ground.

The duration of fog is mainly related to the humidity of the local climate: generally speaking, the short fog in arid areas dissipates within 1 hour, while the long fog in humid areas is the most common and lasts for about 6 hours.

The cause of fog

When the water vapor contained in the air reaches the maximum, it reaches saturation. The higher the air temperature, the more water vapor it contains. 1 m3 air, the maximum amount of water vapor can be 6 or 36 grams at 4℃; When the temperature is 20℃, the maximum water vapor content in 1 m3 air is 17 and 30g. If the air contains more water vapor than saturated water vapor at a certain temperature, the excess water vapor will condense out. When enough water molecules combine with tiny dust particles in the air, the water molecules themselves will combine with each other and become small water droplets or ice crystals. The water vapor in the air exceeds saturation and condenses into water droplets, which is mainly caused by the temperature drop. This is why it is foggy in autumn and winter morning.

If the geothermal energy is lost, the temperature drops and the air is quite humid, then when it cools to a certain extent,

Part of the water vapor in the air will condense out and become many small water droplets, suspended in the air layer near the ground, forming fog. Both it and clouds are caused by temperature drop, and fog can actually be said to be a cloud near the ground.

The temperature is higher during the day, so the air can hold more water vapor. But at night, the temperature drops and the capacity of water vapor in the air decreases. Therefore, some water vapor will condense into fog. Especially in autumn and winter, due to the long nights, there are not many opportunities without Feng Yun, and the ground heat dissipation is faster than that in summer, which makes the ground temperature drop sharply, so that the water vapor in the air near the ground can easily reach saturation in the middle of the night, condense into small drops and form fog. In autumn, winter and spring, when the temperature is lowest in the morning, the fog is thickest.

Types of fog

1, radiation fog: after sunset, the hot air on the ground radiates to the sky, and the cooled ground condenses the air nearby. Wet air will drop below the dew point, forming countless small water droplets suspended in the air, which is radiation fog. It mainly appears in the early morning of autumn or winter, with clear weather and weak wind, and will naturally dissipate shortly after sunrise or after the wind speed increases. Most of them appear at night and early morning when the sun is shining, the breeze is blowing gently, and the water vapor near the ground is abundant and stable or there is inversion.

2. advection fog: Warm and humid air moves horizontally, passes through the cold ground or water surface, and gradually cools to form fog, which is called advection fog in meteorology. In Mao Mao, this fog is often accompanied by rainy weather.

3. Evaporation fog: that is, cold air flows through warm water. If there is a big difference between the air temperature and the water temperature, the water vapor will condense into fog because the cold air near the water surface evaporates a lot of water vapor. At this time, there is often an inversion layer on the fog layer, otherwise convection will make the fog dissipate. Therefore, the evaporation fog has a small range and weak intensity, and generally appears around the pond in the second half of the year.

4. uphill fog: this is the fog produced by the humid air rising along the hillside and adiabatic cooling to supersaturate the air. This humid air must be stable and the slope of the hillside must be small, otherwise convection will form and it is difficult to form fog.

5. frontal fog: It often appears near the front where cold and warm air meet. Generally speaking, there will be continuous rain after fog. Before and after, but mostly near the warm front. The fog in front of the front is formed because the raindrops in the warm air cloud above the front fall into the ground cold air and evaporate, which makes the air supersaturated and condensed. The fog behind the front is formed by warm and humid air moving to the area originally occupied by cold air before the warm front and cooling to supersaturation. Because the fog near the front often moves with the front, the army often uses this frontal fog to cover the troops and make sudden attacks on the enemy.

6. Mixed fog: Sometimes the fog formed by two reasons is called mixed fog.

7. Smoke: Generally, smoke is a solid-liquid mixed aerosol composed of smoke and fog, such as sulfuric acid smoke and photochemical smoke.

8. Valley fog: This usually happens in the valley in winter. When the heavy cold air moves to the valley, the warm air also produces the phenomenon of inversion and temperature rise when passing through the top of the mountain, resulting in valley fog, which can last for several days. /p- 1 146349882708 . html

9. Ice fog: Any kind of fog will produce ice fog when water spots condense into borneol. It is usually formed when the temperature is below freezing point, so it is common in the north and south poles. In the book Environmental Monitoring, it can be divided into dispersed aerosol and condensed aerosol according to its morphology. The liquid at room temperature, which is atomized by splashing and spraying, is dispersed in the atmosphere to form dispersed aerosol. When heated, liquid turns into steam and escapes into the atmosphere. When cooled, it condenses into tiny droplets and forms condensed aerosol. The particle size of fog is generally below 65438 00μ m ... . . . . . . . . . . .