AEROSOLS

From Big Medical Encyclopedia

AEROSOLS (grech, aer air + lat. sol[utio] solution) — the disperse systems consisting of a gaseous fluid in a cut are weighed firm or liquid particles.

And. have extremely wide spread occurance not only in the nature (fogs, clouds, soil, volcanic, vegetable dust, etc.), but also in production activity of the person since are formed at the most various ways of receiving, processing and use of various materials in the industry, agriculture and on transport.

Formation of a dispersed phase of solid matters takes place at explosions, burning, blows, grind, friction, crushing, drilling, grinding and many other processes. Dispersion of liquids happens during the spraying, spraying etc. And., formed owing to crushing of solid and liquid matters, call And. crushing. Owing to cooling and formation of a supersaturated steam, a particle to-rogo are well condensed on «kernels of condensation» (the most fine firm or liquid particles, gas ions), and also by chemical reactions between two or several chemical substances (as a result to-rykh new substance with smaller steam tension is formed) there is an education And. condensation. E.g., at combustion of zinc it is formed And. zinc oxides (ZnO), phosphorus — phosphorus pentoxide (P 2 O 5 ), at interaction of ammonia and hydrogen chloride it is formed And. ammonium muriate (NH 4 Cl). At decomposition on air or hydrolysis of chloride salts of various elements (metals, metalloids) complex Paro-gas-aerosol mixtures, a dispersed phase are formed to-rykh consists of solid particles of oxides of elements and particles of fog salt to - you, and the dispersion medium consists of air, chlorine, vapors of other possible connections which are formed at reaction with oxygen and water vapors of air. At heat treatment of polymeric materials (plastic, etc.) Paro also-gas-aerosol mixes containing firm, liquid particles, gases and vapors of various chemical substances in the structure are formed. During the cooling on air of vapors of metals (lead, copper, aluminum, vanadium, beryllium, etc.) are formed And. condensation of metals and their oxides. Most often education takes place And., the dispersed phase to-rykh contains the particles which are formed as as a result of crushing, and steam condensation. Emissions of the metallurgical enterprises, thermal power plants, boiler rooms concern to them, And., formed at pyrometallurgical processes, welding works, etc.

the Physical and chemical characteristic of aerosols

Various And. (smokes, fogs, dust, bioaerosols, radio aerosols) have a number of the general properties since particles of a dispersed phase of these systems have approximately identical sizes: 10 - 3 — 10 - 7 see. As well as lyosols (see. Colloids ), And. have kinetic and modular stability. Their kinetic stability is big that is provided with small particle sizes and small density of the air environment. Modular stability And., especially with a solid dispersed phase, it is small owing to. small electric charge on particles (no more than 10 elementary particles of a charge). Almost each collision of particles leads to their adhesion (coagulation) therefore average partial concentration of these systems makes only 10 7 particles/cm 2 against 10 15 particles/ml in lyosols. Concentration of particles of v of t decreases over time on the equation: 1/v — 1/v 0 == Kt, where v 0 — initial partial concentration, To — a constant of coagulation. Water fogs and clouds are more concentrated systems, agregativno steadier in connection with existence of rather big electric charge on a surface of droplets. The charge of the last is caused by polarity of water molecules and their correct orientation in a surface layer of a drop.

Deprived of a charge And. are not capable to to an electrophoresis (see), but are capable to a termoforez and a photophoresis. Termoforez — spontaneous removal of particles And. from a source of heat — is caused by the fact that molecules of air before a particle get warm stronger and with a bigger force strike in a particle, than molecules of air behind it. Termoforez is followed by thermoprecipitation — sedimentation of particles on cold sites of unevenly heated body. A photophoresis — spontaneous movement of particles And. from a light source (a positive photophoresis) or to a light source (a negative photophoresis). The type of a photophoresis depends on the size, a form and transparency of a particle. The reason of a photophoresis is similar to the reason of a termoforez. Termoforez and a photophoresis along with wind regulate the movement of clouds.

Optical properties — reflection, dispersion and light absorption And. — depend on the size, a form and the nature of particles. If particle size is less than a half of the wavelength of incident light, then And. scatter light and submit to the law of Re of leu. Blue color of the sky and red color of a dawn is explained by it. Tyndall's cone is especially bright in And. owing to a big difference in indices of refraction of air and a dispersed phase. Destruction And. make or for the purpose of catching of valuable products from industrial smoke, or for the purpose of purification of air of harmful impurity, or for destruction of gradovy clouds and fogs. For this purpose use the devices constructed on various principles: change of speed and flow direction And. (cyclones, multicyclones, rotational catchers), action of electric field (electric precipitators), filterings (mesh filters, fibrous filters, Petryanov's tissue), action of ultrasound, absorption of particles And. water (conditioners, scrubbers).

Depending on particle sizes distinguish: 1) dust (particle size of a dispersed phase more than 10 microns), 2) clouds (10 — 0,1 microns), 3) smokes (0,1 — 0,001 microns). The last by the sizes are close to molecules and are in Brownian motion, thanks to Krom the probability of collision of particles is high, they coagulate, get the bigger size and settle. Coarse particles settle with acceleration according to Newton's law, small — with a uniform speed (Stokes's law). Than the degree of dispersion is higher And. more number of particles in unit volume, the quicker goes coagulation with the subsequent sedimentation. Unequigranular And. coagulate quicker, than from disperse.

Particle size defines also their ability to get into respiratory tracts. Particles up to 5 microns in size are capable to get into alveoluses and to be late in them (respirabelny fractions). Particles of 10 and more micrometers are late in upper respiratory tracts and bronchial tubes, in alveoluses are not brought (tab.). Than the degree of dispersion is higher And., that their specific surface (a total surface of particles in unit volume), chemical and physical is higher. - chemical activity (solubility, ability to diffusion, etc.). Specific weight of particles matters for the speed of their sedimentation. On a chemical origin distinguish And. organic, inorganic, mixed, and on toxicity — toxic and non-toxic.

For assessment of danger and harm And. for health along with a degree of dispersion the main indicator is weight concentration of particles in unit volume And., expressed usually in milligrams on cubic meter of air.

At hit in an organism And. are capable to cause dust occupational diseases: Pneumoconiosis, bronchitis, diseases of upper respiratory tracts, pneumomycoses, injuries of eyes, skin. Toxic And. cause acute and hron, poisonings. And. reduce transparency of the atmosphere and access of solar radiation to the Earth's surface, oppress growth of plants, speed up fogs in industrial centers, pollute the environment that worsens sanitary living conditions of the person. Besides, And. cause economic damage, causing damage of the production equipment, buildings, carrying away valuable materials with emissions.

Also the useful role of aerosols is big. Nek-ry medicinal substances are used in a look And. for inhalation at treatment of diseases of a respiratory organs, for irrigation of wounds, integuments (see. Aerosoltherapy ). In the industry in an aerosol state fuel (coal and oil), catalysts is used. With the help And. metallic coatings (a plasma dusting), coloring of cars and other surfaces are carried out. And. apply to fight against insects — carriers of diseases of animals and the person, with wreckers of page - x. cultures (use of toxic chemicals by spraying from airplanes, by means of sprays, aerosol bombs, checkers, etc.).

Aerosols radioactive — firm or liquid particles, to-rye contain radioisotopes. Radioactive properties A. are caused by radiation properties of radionuclides, related. Except the indicators inherent usual And., radioactive And. are characterized by the size of radioactivity in a particle, distribution of radioactivity on its volume and function of distribution of radioactivity between particles of various sizes. Concentration radioactive And. in air it is expressed as the number of the radioactivity which is contained in unit volume of air. For measurement of concentration radioactive And. they are besieged on filters, passing a certain air volume, and then measure by the corresponding radiometric or spectrometer methods depending on type and a radiation energy of radionuclides radioactivity on the filter.

By origin radioactive aerosols share on natural and artificially radioactive. Natural radioactive aerosols are formed as a result of allocation of crust of radioactive rare gases (radon, thoron and an actinon) and education in the course of their disintegration of atoms of affiliated radionuclides, to-rye join the particles which are in the atmosphere. Therefore size and future natural radioactive And. are defined by the size of atmospheric aerosols (0,001 — 10 microns) and their loss on the earth. Affiliated radionuclides of uranium and thorium together with miner dust form natural radioactive And. at extraction of uranium and thorium ores, and also at production of the nek-ry non-radioactive minerals (lead, coal, phosphatic fertilizers) having impurity of uranium in fields. Artificially radioactive And. are formed as a result of nuclear explosions, at technological or emergency emissions of the enterprises of the atomic industry, at various processes on processing of hard or liquid radioactive materials, during the operation of nuclear reactors, particle accelerators.

Main danger radioactive And. for the person — hit in an organism. At receipt through a respiratory organs destiny radioactive And. it is caused not only physical. - chemical properties of the bearing inert particle (a state, the size), but also physical. - chemical properties of the related radioisotopes (rinsability, solubility). The radioisotopes coming to a human body in a look And. at inhalation, or are deposited in tissues of a lung, or are absorbed in blood, being distributed in various bodies and fabrics. Almost insoluble radioisotopes it is long are late in lungs and limf, nodes, irradiating directly their fabrics while readily soluble are quickly absorbed in blood, irradiating other body tissues. Under production conditions level radioactive And. in the USSR it is regulated by «Standards of radiation safety» (NRB-69) the size of annual marginal receipt for personnel in microcurie a year. Radioactive And., getting on integuments, can cause beam burns of skin, and also be absorbed in blood. Radioactive And., both natural, and artificial, settling from the atmosphere on the earth, contaminating water, the soil, vegetation, can come to a human body or an animal with foodstuff of a plant origin or to get at a pasture to an organism of page - x. animals, and then with meat products and milk in a human body.

Attempts to use radioactive are made And. for the diagnostic purposes in clinical practice. And., hl. obr. liquid or the colloids containing 198Au 99mTc or other radioisotopes, apply to a research of a functional condition of lungs. However big advantages in comparison with the radioactive gases applied to this purpose at And. no.

Biological aerosols represent aerodynamic system, in a cut firm (dust And.) or liquid (drop And.) the dispersed phase contains biologically active substrate in a species of microorganisms (bacteria, rickettsiae, viruses, tsatogenny fungi) or their toxins. Biological And. evaporations liquid, drying and rise with dust of dry excrement from sick animals and the person result, and also at allocation sick with an airborne way of causative agents of .nek-ry infectious diseases (pulmonary plague, natural smallpox, flu, etc.), and sometimes and bacilli carriers.

On fractional disperse structure biological And. treat unequigranular systems. Particle size of these And. fluctuates over a wide range — from the tenth shares to tens and hundreds of micrometers. Their behavior in the atmosphere submits to the general physical. to patterns. Activity biological And. it is caused by existence in its particles of the viable pathogenic bioagent.

In a human body biological And. get generally through a respiratory organs. Infection through a conjunctiva is carried out by particles And. also depends on their concentration and biological activity.

The striking effect biological And. generally depends on character of an infestant and size of the inhalated dose of the bioagent, edges in turn is defined by concentration of live microbes in inhaled air (biological concentration), lasting inhalations and the volume of lung ventilation of the infected subject. Concentration of the bioagent and consequently also a dose first of all are defined by degree of biological stability And.

Aerosols of military value. In a look And. OB taken advantage of nek-ry foreign armies can be applied in the military purposes (see. Chemical weapon ) and herbicides (see). Defeats of people radioactive And. can arise at explosions of nuclear ammunition (see. Nuclear weapon ). Use of OB in the form of high-disperse And. significantly increases their striking efficiency. Parameters A. (aggregate state of a phase, fraktsionnodispersny structure, concentration) OB depend on the following factors: physical. - chemical properties (firmness, aggregate state), a method of dispersion (explosion of ammunition, spraying by means of aerosol generators, combustion), weather conditions (a condition of the atmosphere), a land relief etc. Therefore the fractional and disperse structure of an aerosol of OB can hesitate from its high-disperse forms (fogs, smokes with a diameter of particles from 0,001 to 0,1 microns) to drop and liquid forms with a diameter of particles from several micrometers (3 — 5) to tens (50 — 70) and even (200 — 400) hundred micrometers. Life time of a cloud And. depends on a volatility of OB: unstable OB (t ° Kip to 120 — 140 °) at explosion of ammunition get to a prizemny layer of the atmosphere in the form of steam, resistant (t ° kip higher than 140 °) — in the form of fog, and OB having very high temperature of boiling — in the form of poisonous smokes. Extent of defeat by an aerosol of OB is defined by properties and amount of the substance which got into a human body.

The radioactive aerosols which are one of the striking factors of nuclear weapon represent mix of particles of «splinters» of division of nuclear explosive substances, not divided part of a nuclear charge (uranium, plutonium), parts of elements of ammunition with the induced radioactivity, parts of atmospheric dust and the soil which turned in And. At air explosion radioactive And. are formed generally at the expense of materials of ammunition, atmospheric dust and moisture of air. Average particle sizes A. after steam condensation of water are equal to several micrometers. Owing to the small sizes and rate of sedimentation radioactive And. a long time remain in the atmosphere and are carried away by air flows on long distances, infecting extensive territories. In the greatest number they are formed at land and superficial underground nuclear explosions due to involvement in a cloud of explosion of huge amounts of soil. The formed cloud of explosion consists of radioactive and non-radioactive particles And., the size to-rykh fluctuates from several micrometers to several millimeters. The striking action radioactive And. can depend on specific conditions of formation of a cloud. Extent of defeat depends on quantity radioactive And., got to an organism with food stuffs, water, at immediate effect on open body parts and at inhalation.

The aerosols of herbicides of defoliants intended for destruction of vegetation can cause also poisonings of the people who are in the territories subjected to processing.

By methods of a research A. the microscopy, ultramicroscopy, including the line ultramicroscopy allowing to define concentration and to carry out dispersion analysis of particles are. A big stride was use of a submicroscopy for the analysis of a form, structure, particle sizes high-disperse forward And., to-rye could not be investigated at light microscopy. The most important in hygienic practice is the gravimetric method of definition of weight concentration of particles by means of their sedimentation on filters by soakage of dusty air with the subsequent weighing and the chemical analysis of a dispersed phase for the purpose of establishment of contents in it free and connected silicon dioxide (mineral raise dust), toxic agents, etc. Gravitation measurements, the chemical analysis and definition of a degree of dispersion of particles on the mass of fractions allow to give rather omnibus estimate from the point of view of harmful action And. on human health. The combination of these methods is applied for health control of air of workrooms and the atmosphere of the inhabited places. Sometimes apply calculating (konimetrichesky) methods (number of particles in unit volume of air), to-rye do not give an idea of the mass of the substance operating on an organism at inhalation And., therefore these methods were not widely adopted.

For the hygienic characteristic And., besides, apply definition of solubility of particles And. in biological environments (blood serum, a gastric juice, water, etc.), electric charge of particles, a specific surface of particles. Overseeing by working conditions and the state of health working in contact with And., pilot studies on animals established maximum allowable concentration of the harmful substances which are in a look And. in air (see the Art. about separate substances, e.g. Beryllium, Lead, etc.). These concentration are criterion for evaluation of a condition of the atmosphere of workrooms and the inhabited places and form a basis for implementation of recreational actions. See also Aerosol devices.




Bibliography: Burstein A. I. Methods of a research of dust content and smoke of air, Kiev, 1954, bibliogr.; Vigdorchik E. A. A delay of aerosols at breath, L., 1948, bibliogr.; Gibbs V. Aerosols, the lane with English, L., 1929, bibliogr.; Greene X. and Lane V. Aerosols — dust, smokes, fogs, the lane with English, L., 1969, bibliogr.; Deryagin B. V. and Vlasenko G. Ya. Line and ultramicrophotometric method of dispersion analysis, Kolloidn. zhurn., page 13, century 4, page 249, 1951; Detri Zh. The atmosphere shall be pure, the lane with fr., M., 1973; Standards of radiation safety (NRB-69), M., 1972; At and y t - lou - Heat R. and Patterson G. S. Dy, researches in the field of aerodis-persny systems, the lane with English, M. — JI., 1934; Fuchs H.A. Mechanics of aerosols, M., 1955, bibliogr.; Hukhrina E. V. and Tkachyov V. V. Pneumoconiosis and their prevention, M., 1968, bibliogr.; Enton N. Development and designing of a series of exact detectors for measurement of radioactive aerosols and their use for radiation control, in book: Dosimetry of ionizing radiation, the lane with in., page 287, M., 1956, bibliogr; Task group, deposition and retention models for internal dosimetry of the human respiratory tract, Hlth Phys., v. 12, p. 173, 1966, bibliogr.

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A. V. Roshchin; K. G. Gapochko, G. I. Kremlev (soldier.), L. A. Ivanova (physical. - chemical), Yu. D. Parfyonov (I am glad.).

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