What are the hazards of fog?

Fog is a weather phenomenon in autumn and winter. The phenomenon that a large number of water droplets or ice crystals suspended in the near-surface layer make the horizontal visibility less than 1 km. There are two basic conditions for the formation of fog: one is that the air near the ground is rich in water vapor, and the other is that the ground temperature is low. In winter and early spring in Beijing, cold air from the north and warm and humid air from the south often meet in North China, so it is easy to have gray weather after snow, rain and fog at the junction.

According to the different causes of fog formation, it can be divided into radiation fog and advection fog. Radiation fog is formed when the temperature drops by radiation at night and the water vapor in the ground air is saturated. This kind of fog mostly appears at night or in the morning, when the sun is shining, the breeze is blowing gently and the water vapor near the ground is rich. Advection fog is caused by the horizontal movement of air. Fog is also a kind of disastrous weather, and many accidents such as road traffic, flight and shipping are caused by fog. At the same time, the combination of fog and pollutants in the air will also bring great harm to people's health.

Fog is the "ruthless killer" of transportation. When there is dense fog, visibility is very poor, and sometimes only a few meters or dozens of meters away can be seen, which makes the fog near the ground very low and the line of sight blurred. According to statistics, traffic accidents caused by bad weather such as fog in expressway account for about1/4 of the total number of accidents; For the sake of aviation and the safety of passengers, the airport must be closed in case of foggy weather. According to historical statistics, domestic flights can't take off and land normally, accounting for 78.9% due to fog, and foreign flights account for 57%. River transportation is also deeply poisoned by fog.

Due to the high humidity, fog can easily damage the porcelain insulators of high-voltage transmission lines, leading to pollution flashover, power grid cracking and large-scale power outages. In recent ten years, "pollution flashover" caused by heavy fog has occurred in North China and Northeast China, which has seriously affected people's production and life.

Fog also has an adverse effect on agricultural production. Long-term fog blocks the sun, hinders the respiration and photosynthesis of crops, reduces the storage of carbohydrates, and makes crops weak. The ultraviolet rays in the sun are reduced by fog drops and are vulnerable to pests and diseases. In foggy areas, insufficient sunshine time will delay the flowering and poor growth of crops, thus affecting or reducing the quality and yield of products.

In recent years, due to climate warming, temperature rise, the content of water vapor in the atmosphere increases, human activities lead to the increase of pollutants in the atmosphere, which leads to the increase of condensation nuclei of water vapor condensation, and the frequency and intensity of fog tend to increase. Fog droplets in the air often carry bacteria and viruses, which will also affect the diffusion of urban pollutants and even aggravate the toxicity of substances such as sulfur dioxide. Therefore, people should go out less in foggy days, let alone exercise in foggy days, so as to avoid inhaling more harmful substances in foggy days and causing harm to the body.

Like other weather phenomena, fog is not without its merits. The natural beauty created by fog has become an important tourism resource. Fog can also purify the air. The air will feel fresh after the fog. This is because the smoke particles and dust in the air are removed and dissipated by fog drops, just as the air with impurities is washed after rain and snow, so that the air is purified.