How is urban fog formed, and is it harmful?

Heavy urban pollution leads to condensation of water vapor and the formation of fog. There is harm!!

Formerly known as the "Fog Capital", London was heavily polluted during the First Industrial Revolution.

1.Fog is a phenomenon in which a large number of water droplets or ice crystals are suspended in the near-surface layer, making horizontal visibility 1 km smaller. Fog can be divided into many types, the common ones are radiation fog and advection fog.

Radiation fog is formed after the ground air reaches the state of water vapor saturation due to radiative heat dissipation and cooling at night, and this kind of fog mostly appears at night or in the morning when it is clear, breezy and relatively abundant near the ground water vapor. Advection fog is caused by the horizontal movement of air. Fog is also a disastrous weather, many highway traffic, flight and shipping accidents are caused by fog, at the same time, fog and air pollutants combined will also bring great harm to people's health.

2.A fog is a visual aggregate of a large number of fine water droplets (or ice crystals) suspended in the atmosphere near the surface. To distinguish between fog and clouds, simply determine whether they touch the ground or not.

The appearance of fog leads to a significant reduction in horizontal visibility on the ground. According to the World Meteorological Organization, visibility is called fog when visibility is reduced to less than 1 km, and light fog when visibility is between 1 and 10 km. The common fog is mostly milky white.

In urban and industrial areas, the fog can be yellowish or grey due to the influence of pollutants in the air. Ice fog can be dark gray.

3.Fog is formed mainly by the condensation of water vapor in the air reaching (or nearing) saturation on the condensation nucleus. There are generally two ways in which fog forms:

1) Advection fog, radiation fog, uphill fog, etc. due to the decrease of air temperature;

2) Evaporation fog, frontal fog, biological fog, etc. due to the increase of water vapor in the air.

4.According to the microstructure and temperature of fog, it can be divided into three types: warm fog, supercooled fog and ice fog.

1) Warm fog consists of water droplets with a temperature higher than 0;

2) Supercooled mist consists of supercooled water droplets with a temperature below 0;

3) Ice fog is made up of ice crystals. Supercooling fog can often be eliminated by artificial catalysis.

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.

Formation condition 1: cooling.

How fog is formed.

This 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.

Formation condition 2: humidity.

How fog is formed.

Humidity is a necessary condition for the formation of fog, and it is also a raw material for fog, if there is not enough humidity and 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.

Formation condition 3: condensation nucleus.

The water vapor conditions are there, the cooling conditions are also there, and at this time it depends on whether it can condense, and the fog will only form if small water droplets or ice crystals are formed. 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.

Foggy weather has a great impact on traffic. In foggy weather, airplanes cannot take off and land, and cars and ships are prone to traffic accidents due to poor visibility. There is also a certain harm to the production of ants in agriculture.

If there is heavy fog for several days, the crops will lack light, which will affect the growth and induce diseases. If the wheat is heading and encounters heavy fog for more than 3 consecutive days, it is easy to cause scab disease. Fog is also harmful to human health.

According to measurements, the proportion of acids, alkalis, salts, amines, phenols, dust, pathogenic microorganisms and other substances harmful to the human body contained in the droplets is dozens of times higher than that of ordinary atmospheric water droplets. If people are active in the fog, they will inhale these harmful substances in the fog, thereby inducing or aggravating many diseases such as tracheitis, pharyngitis, and conjunctivitis.

It is related to the air temperature, when the water vapor reaches its maximum saturation and the temperature decreases.

01. The cause of the formation of fog.

1. The conditions for the formation of fog are cooling, humidification, condensation nuclei, and increasing water vapor content; The main reason is that due to the loss of heat from the ground, the temperature drops, and the air is quite humid, when it cools to a certain degree or degree, 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.

2. Experiments have proved that when white light shines on a transparent object, the light it transmits is mainly the light of the same color as the transparent object, and other colors are absorbed by the transparent body.

If a transparent object can transmit light of all colors, then the transparent object is colorless, such as ice.

However, when the water turns into fog, many reflective surfaces are formed.

At this time, the light is not transparent, but is reflected, that is, the light of various colors is reflected, so that the fog becomes white.

02. Why is it the same fog, some are rainy, and some are sunny.

This is explained by the knowledge of meteorology. As long as the water vapor content of the lower air is high, the water vapor will condense into fog when the temperature drops sharply at night. Fog has radiant fog, which is fog that forms when it is relatively sunny and stable.

As soon as the sun comes out and the temperature rises, the fog disappears naturally. In this regard, the folk saying is: "The fog is thick in the morning, and the weather will be sunny for a long time."

The sun is in the fog, and the sun is broken. "In the morning the ground is covered with fog, despite the drying of rice. When people see radiation fog, they often "ten fogs and nine sunshines".

That's what He Lu said.

In autumn and winter, after the cold air from the north goes south, with the weather becoming clear and the sun is irradiated, the content of moisture in the air gradually increases, and it is easy to form radiation fog, so the fog in autumn and winter can often predict tomorrow's good weather.

In spring and summer, fog is different, it mostly comes from the warm and moist air flow from the sea, and when it hits colder ground, the air below also becomes cold, and the water vapor condenses into fog. This fog is called advection fog. It is formed by the sudden cold of warm and moist air from the sea that invades the continent.

When these warm and humid air currents meet the cold and dry air of the mainland, it will naturally be cloudy and rainy. So spring and summer fog heralds rainy weather.

Fog is so closely related to the weather that you can see how the weather changes by looking at it. However, the above explanations of radiation fog and advection fog are only in general terms. The relationship between fog and weather is not so simple, and there are many complex contents, so it cannot be rigidly copied, but must be analyzed on a case-by-case basis.

In other words, in order to accurately see the fog and know the sky, it is necessary to make multi-faceted observations, analysis, and comprehensive judgments.

The conditions and causes of fog formation are caused by the maximum saturation of water vapor and the decrease in temperature.

This is because when the water vapor in the air reaches a certain limit, it will reach a saturated state. This saturation varies with the temperature, with the higher the temperature, the more water vapor can be contained in the air, and vice versa.

When the water vapor in the surface air is greater than the amount of saturated water vapor at the same temperature, the excess water vapor will condense, and when the condensed water vapor is combined with the tiny dust particles in the air, it becomes small water droplets or ice crystals, which is what we call fog.