Dust is constantly present in the air. You may not see it, but it is always there. This substance is suspended in the air, solid particles ranging in size from about fractions to hundreds of microns.
Dust is everywhere
No matter how much you clean your shoes and sweep the floor, the ubiquitous dust will still appear. Basically, it is brought into the house along with the air from open windows and doors. The sources of dust in the atmosphere are very diverse: soil and sea water salts that enter the air, volcanic emissions, and fires. Industry and transport are the main anthropogenic sources.
The dust that we breathe can be of local origin or brought from afar. For example, in an urban atmosphere during "normal" periods, dust from local sources averages about 70%.
The dust content in the air of a megalopolis, due to large-scale transport of air masses, in the least "dusty" periods - about 15-40 μg / m3 and becomes higher in years of higher volcanic activity. This value can be multiplied by large forest fires. Thus, during forest fires in a city, the dust content can exceed the average "quiet time" by tens of times.
Dust comes in a variety of chemical compositions. These are compounds of silicon, beryllium, aluminum, cadmium and other metals, products of road surface wear and incomplete combustion of fuel (coal particles and soot aerosol), spores of microorganisms and plant pollen, and other particles of organic origin. Secondary inorganic compounds (sulfates, nitrates, ammonium), which are obtained as a result of chemical reactions in the atmosphere, are isolated separately.
The distribution of particles of different chemical nature in the atmosphere has its own geographical features.
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So, if in Eastern Europe the main contribution to air pollution is made by heating products and vehicles, in Western Europe, secondary inorganic aerosols prevail among dust particles. In the industrially developed regions of Northern Europe and near large European cities, the total content of dust particles is determined mainly by anthropogenic sources, and in the countries of Southern and Southeastern Europe - by soil weathering (the so-called erosion dust).
Two conditions are necessary for the formation of erosive dust: dryness and wind. The dry surface layer of the earth is easily crumbled, soil particles in a dry state are weakly held together and can be lifted into the air by the wind. With a lack of vegetation, these processes are significantly enhanced: the green "clothing" protects the soil layer both from drying out and from too strong wind, which loses speed in the vegetation cover and is not able to "reach" the soil surface. That is why, for example, dust storms occur mainly in desert and semi-desert regions, less often in steppe regions, and in forest-steppe and forest regions - in exceptional cases (as a rule, during severe drought).
In recent years, dry lawns resulting from excessive mowing have become a significant source of dust in many large cities. Instead of mowing the grasses 1-2 times a year, the authorities, overzealous, destroy the grass cover and contribute to the drying out of the soil.
The nature of the spread of dust particles in the atmosphere depends on their size. Large particles and part of medium ones (larger than 1 micron) settle within several hours or a few days and therefore, as a rule, are transported over relatively short distances (although in some cases they can travel hundreds of kilometers if the dust is at a significant height). Smaller particles (highly dispersed fraction) can stay in the atmosphere for up to 10-20 days and spread during this time throughout the hemisphere (exchange between hemispheres through the equatorial zone is difficult).
The table shows the characteristic values of the settling velocity of particles of different sizes in still air and the superimposed on this settling displacement due to the Brownian motion. As can be seen, for particles with a size of 2.5 microns, the settling rate is about 15 times lower than for particles with a size of 10 microns, and is about 0.2 mm / s, that is, it can be compensated for even by a very slight upward air flow. For particles smaller than - 0.5 microns, the speed of movement prevails over the speed of their settling, and therefore such finely dispersed (ultrafine) suspensions can practically not settle.
Dust particles in the atmosphere have a great influence on the climate, since they absorb part of the solar radiation, and also participate in the formation of clouds, being the nuclei of condensation.
Dust and health
How does dust affect health? Both chemical composition and particle size are important here. Large particles (larger than 5-10 microns) are usually retained in the upper respiratory tract, while smaller ones are able to penetrate into the lungs. Accumulating there, even chemically inert dust particles (for example, quartz or coal dust) can lead to micro-damage to lung tissue and cause chronic respiratory diseases. A prolonged inflammatory reaction in the lungs ultimately affects the work of the heart, leading to the development of cardiovascular diseases. For this reason, in many countries there are standards for the content of medium-dispersed particles (up to 2.5 or up to 10 microns in size) in the air, and more finely dispersed dust (up to 2.5 microns) is considered more hazardous. Dust chemical composition,including the presence of compounds of heavy metals and toxic organic compounds in it, brings its own "specificity" to the impact of dust on the human body.
According to the World Health Organization, approximately 3% of deaths from cardiopulmonary pathology and 5% from lung cancer are associated with high levels of particulate matter in the air. An increase in the content of dust particles in the air by only 10 μg / m3 can be the reason for an increase in the number of deaths by 0.5% (and for people over 75 years old - twice as much).
These are terrible numbers, it is not for nothing that there are many legislative restrictions on the level of dustiness in the world in the world.
But for all the importance of the development of technological methods for combating dust formation, one of the main ways to maintain air purity is the preservation and development of natural areas - not only on a planetary scale, but even on the scale of a lawn (lawn) in the courtyard of a city house or on a highway dividing strip. Moreover, the role of natural communities is not limited to "passive" protection - mechanical filtration of dust. A living ecosystem not only prevents its spread, but also recycles dust, absorbing suspended particles settling from the atmosphere due to the activity of many living creatures living in the soil and on its surface.
House dust
Household dust consists of hair, dead skin particles, cobwebs, lint of fabric and sometimes light debris and scraps, which are held together by electrostatic forces and felt-like tangles.
A man brings in dust with outer clothing; a person himself, according to statistics, for example, falls out about 100 hairs per day. If there are pets in the apartment, their wool will be included in the dust.
Even in a tightly locked apartment with closed windows, about 12 thousand dust particles settle per 1 square centimeter of the floor and the horizontal surface of furniture in two weeks. This dust contains 35% mineral particles, 12% textile and paper fibers, 19% leather flakes, 7% pollen, 3% soot and smoke particles. The remaining 24% are of unknown origin and cosmic dust.
House dust can contain so-called house dust mites. Despite their closeness to humans, they themselves are practically safe. However, waste products from house dust mites can cause allergies and one of the most common causes of asthma.
If you properly study the composition of the dust, it turns out that it is home to about 5,000 bacteria and another 2,000 species of fungi. The species composition of mushrooms most of all depends on the geographical location of the house, while the bacterial microflora of dust is more influenced by the inhabitants of the house themselves. So, according to it, you can determine which pets live in the room. The presence of cats is indicated by 24 genera of bacteria, and the presence of dogs - 56 genera. Mostly, these bacteria live in the faeces of these animals.
In addition, the dust microflora can be used to calculate the sex ratio in the family. So, in houses where there are relatively few or no women, many bacteria Roseburia and Cogupe-bacterium can be found in the dust (the former live on human feces, the latter are especially abundant on the skin of men). In houses where there are many women, the bacteria Lactobacillus is abundant in the dust - it gets there from the vaginal microflora.
Cosmic dust
Every year, 40,000 tons of cosmic dust, ranging in size from a few molecules to 0.2 microns, settle on planet Earth. It was formed, basically, billions of years ago, during the collision of asteroids, their fall on the surface of planets, during stellar flares and other cosmic and even volcanic phenomena.
Cosmic dust can be distinguished by its astronomical position, for example: intergalactic dust, galactic dust, interstellar dust, near-planetary dust, dust clouds around stars, asteroid dust, comet dust and some minor additives: Kuiper Belt dust, interstellar dust passing through the Solar System, and beta meteoroids.
In the solar system, dusty matter is not evenly distributed, but is concentrated mainly in dusty clouds of different sizes. It was possible to establish this during the total solar eclipse on February 15, 1961 using optical equipment.
Desert dust
In the countries of East Asia, dust storms, including the so-called yellow dust of Mongolia (in Mongolian - tuiren), are a real disaster. According to recent studies carried out at the Aviation Meteorological Center in Ulaanbaatar, such dust storms have increased significantly: if in the 1950s tuiren was observed five times a year, now this number has reached thirty. Another study shows Mongolia had 20 days a year with dust storms in the 1960s, 50 in the 1980s, and 100 in 2010.
Dust storms are caused by global climate change and increasing desertification as a result.
Sudden dust storms pose a serious danger to the population. For example, in May 2008, during a strong sandstorm in Mongolia, 46 people died. However, bad weather is dangerous not only for human health - tuiren causes significant damage to the economies of East Asia.
Countries in Africa and other desert regions suffer from dust storms no less. Spreading by atmospheric rivers, storms can affect the climate of territories located thousands of kilometers from the place of their formation.