Dust called the solid particle size of from 0.01 to 10 microns. Dust particles smaller than 5-10 micron constantly floating in the air, particles of 10 to 50 μm are deposited gradually, and almost immediately settled.
Dust can be very different. Dust is emitted into the atmosphere when burning solid fuel, rich in ash substances in the processing of minerals. She is able to be formed and as a result of natural processes such as volcanic eruptions or the weathering of rocks, and agriculture. During a drought over the fields raging dust storms, and rises over the desert sand dust.
Dust is omnipresent. It seeps through the smallest cracks and holes. It is everywhere: in the cave where they have never stepped in the apartment, the inhabitants of which a long trip, on the plane, rushing above the clouds, and even high above the earth, in the stratosphere.
Tiny salt crystals form dust over the oceans. But it is a negligible amount compared to the dust mass, which occurs on land. Over the ocean the atmosphere is polluted with dust 10 times lower than over the continents.
House dust contains hair and pet dander, parts of feathers, insect parts, hair and human skin, mould spores, nylon, fiberglass, sand, particles, tissues and paper, tiny fragments of materials from which made the walls, furniture and household items.
Dust loves to travel, and it is easy. Its particles are very small and extremely light. They are carried by the wind over great distances, so that the layer of dust settled on your table, you can find Sahara sand, crumb pyramids, the ashes of the volcanoes, the disputes of the South American plants, particles wool kangaroos, marble dust, ancient ruins, pollen French lilies and even cosmic dust from the dusty paths of distant planets, which sang your grandparents when they were young.
Dust is not as harmless as it may seem, so it must constantly fight.
First, basic (up to 80%!) and the most harmful part of household dust consists of microscopic dust mites. They settled in the dwellings of man for a long time, hit them with down and feather birds, and some species with agricultural products. Homemade tick bites and of itself is not dangerous to humans. The problem is the waste of his life - the excrement, which often cause severe allergies. Each mite daily allocates about 20 particles of excrement.
Especially love dust mites live in bedding, because it is full of biological dusts generated from closeprice scales of our skin. A double bed can count about 2 million mites.
Secondly, the dust can absorb on the surface of any substances, including harmful, so in house dust can be found in almost half of the periodic table and more than 100 organic compounds that cause incurable diseases.
Third, except for impurities, dust is full of bacteria (they don't move air freely, and travel on dust particles). One thimble house dust contains 5 000 000 microbes. After the death of microorganisms released bacterial endotoxins, which can also cause allergies. For bacteria that are normal products of metabolism, and for humans and other large animals they are poisonous.
During the day the resident of a large city "passes" through their lungs to 6 billion dust particles, which would fit in two tablespoons.
Dust prevents to produce parts for microelectronics and high-precision instruments. On such productions with her fight for life and death.