Dust refers to solid particles suspended in the air. It is customary to have many names for dust, such as dust, dust, smoke, mineral dust, sand dust, powder, etc. These terms have no obvious boundaries. The International Organization for Standardization stipulates that solid suspensions with a particle size of less than 75 μm are defined as dust. The presence of dust in the atmosphere is one of the main reasons for maintaining the temperature of the Earth. Too much or too little dust in the atmosphere will have a devastating impact on the environment. However, in life and work, productive dust is a natural enemy of human health and is the main cause of various diseases.
Dust presence
Dust is almost everywhere. The soil and rock are weathered and split into many tiny particles that accompany the pollen, spores and other organic particles floating in the air. In addition, many dusts are by-products of industrial and transportation development; the exhaust gases emitted by chimneys and internal combustion engines also contain a large amount of dust, volcanic ash from volcanic eruptions caused by operations such as flour and quarry.
Dust classification
Dust can be classified according to many characteristics. In the control of air pollution, according to the size of dust particles in the atmosphere, it can be divided into:
1. Glowing dust refers to solid particles with a particle size of less than 10 μm in the atmosphere. It can float in the atmosphere for a long time, sometimes called floating dust. Also known as respirable particulate matter, the English abbreviation is PM10.
2. Dust-reducing refers to solid particles with a particle size greater than 10 μm in the atmosphere. Under gravity, it can settle to the ground in a short period of time.
3. Total suspended particulates refer to all solid particulates with a particle size of less than 100 μm in the atmosphere. Also known as total suspended particulate matter, the English abbreviation is TSP.
Professional term 1, powder: small particles of solid matter, called particles, and the state of accumulation of solid particles, called powder.
2. Dust: Fine particles generated by mechanical processes (crushing, sieving, transportation, etc.), which can be dispersed (suspended) in a gas for a certain period of time, called dust. Dust has a wide range of particle sizes ranging from fine to 1/10 μm to hundreds of microns.
3. Soot: Fine solid particles produced by physical and chemical processes, called soot. For example, in the processes of smelting, burning, metal welding, etc., due to sublimation and condensation, the characteristics of soot are that the particle size is relatively fine, below 1 μm.
4. Smoke: Burning black smoke generated from grass, wood, oil, coal, etc., called smoke. The particle size of the smoke is very fine, even below 0.5 μm.
5. Powder: The powder in the process of production, called powder.
Dust effect
The surface water is vaporized into the atmosphere and returned to the ground by precipitation, thus completing the circulation of water. If there is no dust in the air, the water will not condense into water droplets if it is too large. Because the water molecules are small, the water droplets aggregated by it are also small, and the saturated water vapor pressure is large, so it is difficult to form precipitation. When there is dust in the air, it can absorb water vapor into a solution and form water droplets. The saturated water vapor pressure is greatly reduced, making the water vapor easy to condense around it and become cloud, fog, snow, and the like. During this change, the dust acts as a condensation tuberculosis.
The blue sky in the sky is also the result of dust in the atmosphere. Sunlight is composed of red, orange, yellow, green, blue, blue and purple. When the sunlight enters the atmosphere, it will scatter when it encounters dust and water vapor suspended in the air. The shorter the wavelength, the more easily the light is scattered. The higher the density of the air, the stronger the scattered light. The air density decreases with the increase of altitude. Therefore, at a low altitude below 8 000 m, the blue light with a short wavelength is scattered a lot, and humans can see the magnificent landscape of "the autumn water and the blue sky" from the ground. . As the altitude increases, the ability of the atmosphere to scatter sunlight becomes weaker, the sky above 8 000 m turns cyan, and above 13 000 m is dark purple. Above 20 000 m, the sky becomes a dark black due to the disappearance of scattering.
Sunrise and sunset are also the work of dust. When the sun rises above the horizon, the light passes through the dusty atmosphere, and the sun is much larger than when it is shot at noon. At this time, dust and water vapor scatter blue and green light in the sunlight, while red light with a long wavelength passes directly through the atmosphere, so the sun rises in the sun or the sun sets. Under certain conditions, dust also creates a peculiar landscape. In 1883, the Indonesian Clarke volcano erupted and threw a large amount of volcanic ash into the sky. At that time, the sun that people saw in the area was always red, and the landscape lasted for two years. In 1816, the smoke from the Indonesian Java volcano reflected and absorbed a lot of sunlight. As a result, the temperature in the area was reduced that year, and there was a rare miracle without summer, the so-called parasol effect. In short, no dust clouds, fog, rain, snow will disappear, the fiery sun and beautiful rainbow will disappear, and the natural landscape is inferior.
Dust hazard
Dust has also been done, and one of its effects is to pollute the atmosphere and endanger human health. Dust that floats in the atmosphere often contains many toxic components such as chromium, manganese, cadmium, lead, mercury, and arsenic. When the human body inhales dust, particles smaller than 5μm can easily penetrate deep into the lungs, causing toxic pneumonia or silicosis, and sometimes cause lung cancer. Once the pollutants deposited in the lungs are dissolved, they will directly invade the blood, causing blood poisoning, undissolved pollutants, and may be absorbed by the cells, resulting in destruction of the cell structure. In addition, the dust can contaminate the building and cause damage to valuable ancient buildings. Dust that falls on the foliage of plants can hinder photosynthesis and inhibit its growth.
The second thing dust is the explosion hazard. According to legend, as early as in the era of windmills, there have been a series of mill dust explosions. In the 20th century, with the development of industry, dust explosion accidents are more common, and the types of explosive dust are also increasing. According to statistics, between 1913 and 1973, there were 72 more serious dust explosions in the industrial and agricultural sector in the United States alone. A dust explosion occurred in a starch factory in Ohio in 1919. The plant was almost completely destroyed and 43 people were killed. From 1952 to 1975, there were 177 major dust explosion accidents in Japan, with a total of 75 deaths and 410 injuries.
In 1977, a modern grain depot exploded in Louisiana, causing more than half of the grain silos to be destroyed. Even the office building was not spared, 36 people were killed, and direct economic losses amounted to $30 million. The United Kingdom and Canada have also experienced excessive dust explosions in the chemical and paper industries, with only 243 in the UK and 204 deaths and injuries.
On March 15, 1987, an explosion occurred at the Harbin Flax Textile Factory, killing 56 people and injuring 179 people. The plant equipment was severely damaged.
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