What is the difference between clouds and fog in the sky? Is fog related to the impact of environmental pollution?

The clouds floating in the sky are composed of many small water droplets or ice crystals, and some are composed of small water droplets or small ice crystals mixed together. Sometimes it also contains some larger raindrops and ice and snow particles. The bottom of the cloud does not touch the ground and has a certain thickness.

Cloud formation is mainly caused by the condensation of water vapor.

Fog is a visible collection of a large number of fine water droplets (or ice crystals) suspended in the atmosphere near the ground.

To distinguish between fog and clouds, you only need to determine whether they are touching the ground.

The occurrence of fog causes the horizontal visibility on the ground to be significantly reduced. According to the provisions of the World Meteorological Organization, visibility that reduces visibility to less than 1 km is called fog, and visibility that reduces visibility to 1-10 km is called light fog. Common fog is mostly milky white. In cities and industrial areas, fog can appear khaki or gray due to the influence of pollutants in the air. Ice fog can be dark gray.

The formation of fog is mainly caused by the water vapor in the air reaching (or approaching) saturation and condensing on condensation nuclei. There are usually two ways to form fog: (1) advection fog, radiation fog, uphill fog, etc. due to the decrease in air temperature; (2) evaporative fog, frontal fog, biological fog, etc. due to the increase in water vapor in the air.

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 is composed of water droplets with a temperature higher than 0°C; (2) Supercooled fog is composed of supercooled water droplets with a temperature lower than 0°C; (3) Ice fog is composed of ice crystals. Among them, supercooling fog can often be eliminated through artificial catalysis.

There is no direct relationship between fog and environmental pollution. However, when air pollution is serious, if heavy fog occurs, it will aggravate the pollution level and even cause serious consequences.

For example

On December 5-8, 1952, a disaster struck London, England. There is a high pressure center over the city of London, located in the Thames River Valley. There has been no wind for several days, and the anemometer reads zero. Heavy fog has shrouded the city of London, and the city is burning a lot of coal in winter. The soot and dust emitted accumulate and scatter in the windless state. Smoke and moisture accumulate in the atmosphere, causing the sky above the city to be filled with smog for four or five consecutive days, with extremely poor visibility. Low. Under such weather conditions, planes were forced to cancel flights, cars had to turn on their lights even when driving during the day, and pedestrians found it extremely difficult to walk and had to fumble along the sidewalk.

Because pollutants in the atmosphere continue to accumulate and cannot diffuse, many people feel difficulty breathing, stinging eyes, and tears. London hospitals were overflowing due to a sharp increase in patients with respiratory diseases, and coughs could be heard everywhere in London. In just 4 days, more than 4,000 people died. Even 350 cattle in a grand prize cattle exhibition that was held at the time suffered a tragedy. One cow died on the spot, 52 cows were seriously poisoned, 14 of them were dying. Two months later, more than 8,000 people died one after another. This is the appalling "London Smog Incident".

There are two main culprits causing the London smog incident. The smog emitted by coal burning for heating and industry in winter is the culprit, and the temperature inversion layer is the accomplice. London's industrial fuel and residents use coal for heating in winter. When coal is burned, it produces water (H2O), carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2) and hydrocarbons (CH). and other substances. After these substances are discharged into the atmosphere, they will adhere to flying dust and condense on fog. After entering the human respiratory system, they can induce bronchitis, pneumonia, and heart disease. At that time, the "temperature inversion" phenomenon that lasted for several days, coupled with the continuous emission of smog, made the concentration of smoke and dust in the atmosphere over London 10 times higher than usual, and the concentration of sulfur dioxide was 6 times higher than before. The entire city of London was like a suffocating poisonous gas. Same as the room.

Sadly, this smog incident was not the only one in London. A similar smog incident occurred 10 years later, causing the abnormal deaths of 1,200 people. It was not until the 1970s that London switched to gas and electricity and moved thermal power stations out of the city, reducing urban air pollution by 80%. The horrific smog incident did not happen again in London.