Air Pollution. Sources, kinds and scales of environmental pollutions
Air pollution is due to natural and anthropogenic sources that is to man’s activities. The pollutants may be gases as well as liquids and solid particulate matter. They are detrimental to man, to fauna, to flora, and to material objects of our world.
The World Health Organization of the United Nations defines air pollution and pollutants in the following way: Air is polluted when one or several pollutants are present in the atmosphere at such a concentration and for so long a time that they are harmful to man, animals, plants and material property, cause harm or reduce well-being or disturb appreciably its application. In a more simple way, it may be said that air is polluted when its composition deviates from that of “pure air”. As there is no possibility for a quantitative definition of pure air, the composition of dry air for usual conditions at sea level is accepted as a standard for pure air. This composition is given in table 2.
Table 2. Composition of dry air at sea level conditions
|Component||Concentration ppm = cm3/m3 air|
|Nitrogen Oxygen Argon Carbon monoxide Neon Helium Methane Crypton Nitrous Oxide Hydrogen Xenon Nitrogen dioxide Ozone Ammonia||789,900 209,400 9,300 5,2 1,0-1,2 1,0 0,5 0,1-0,5 0,08 0,02 0,01-0,04 0,01|
This composition includes certain elements like carbon monoxide and nitrogen oxides, which are dangerous pollutants when present in the air beyond of definite concentration. It is always the concentration – the dose – that makes a pollutant.
Paracelsus, a famous physician in the sixteenth century, stated, that almost any substance may be either beneficial or harmful to man, depending on the amount used and the way it is combined with other substances.
The most widespread pollutions of atmosphere get in it basically in two kinds: the suspended particles (aerosols) and gases. Gaseous emissions make up 80-90 % from the general amount of emissions. Chemical compounds of carbon, sulfur and nitrogen is occupied the main place among them.
Carbonic gas or carbon dioxide CO2. In an atmosphere the huge amount of this gas gets as a result of burning of fuel and manufacture of cement. This gas is not poisonous. Carbonic gas is continuously consumed by green plants during photosynthesis. It finds wide application in a life (soda water, «dry ice»). The ecological role of carbonic gas consists in influence on a climate through hotbed (hothouse) effect. Carbonic gas in an atmosphere plays a role of glass in a hothouse. It passes solar radiation, but does not pass in underside infra-red (thermal) radiation of the Earth, creating the hothouse effect.
Carbon oxide CO. Carbon oxide is the most widespread and the most significant on weight the impurity of an atmosphere. This gas is poisonous, has no neither colors, nor a smell. The poisoning by this gas can take place completely imperceptibly. Its poisonous properties are explained that it is absorbed by hemoglobin of blood and instead of oxygen is transferred to various bodies that cause the oxygen famine and destruction of an organism.
In natural conditions the content of СО in an atmosphere is small. The basic share of CO is formed at burning of mineral fuel. Now as a result of activity of a person about 300 million tons of carbon oxide gets in an atmosphere one year. And 70-75 % of emissions are created by burning of gasoline in engines of internal combustion, about 10 % - by burning of coal and fire wood, about 10 % - by burning of household waste products, 5 % - forest fires.
A plenty of carbon oxide gets in an atmosphere from natural sources. The basic natural sources are volcanoes, decomposition of organic substance in reservoirs, electric discharges in an atmosphere, biological processes at the ocean, natural forest fires and others.
Sulfur compounds. The basic sulfur compounds are a sulphurous gas (sulfur dioxide SO2) and hydrogen sulphide H2S.
The main natural sources of sulphurous gas are volcanoes and processes of oxidation of hydrogen sulphide and other sulfur compounds. Industrial sources of sulphurous gas on intensity for a long time have surpassed volcanoes. In the nature there is not mineral fuel, which includes only hydrocarbons. Always there are impurities of other elements, one of them - sulfur. Burning of fuel gives 80-90 % of all anthropogenous sulphurous gas, and burning of coal gives the most of all SO2. The others 10-20 % of sulphurous gas is allocated at melting of nonferrous metals and sulfuric acid production.
Sulphurous gas is poisonous, it irritates respiratory ways, eyes, it causes cough. At the presence of others pollutions (for example, aerosol particles) sulphurous gas can cause death of a person. At the big concentration of sulphurous gas there are a dying of leaves and destruction of plants. At long influence of small concentration chronic damages cause accumulation of harmful substances, destruction of chlorophyll, infringement of growth of plants, reduction in productivity.
Marsh gas or methane CH4. The basic source is the activity of microorganisms at a burial of organic carbon without access of air (for example, at the bottom of bogs). A small quantity of methane (30 %) gets in an atmosphere at extraction of natural gas, oil, coal, and also at burning of plants. More than half of the hydrocarbons are made by people gets in air at incomplete combustion of gasoline and diesel fuel. These emissions contain a plenty of cyclic and aromatic hydrocarbons, which are cancerogenic substances.
Ammonia and nitrogen oxides. The basic gaseous pollutions: ammonia, nitrogen protoxide N2O, nitrogen oxide NO, nitrogen dioxide NO2. Ammonia and nitrogen protoxide have basically a natural origin. Main nitrogen-containing pollutions of atmosphere are nitrogen oxide and nitrogen dioxide. These gases are poisonous. The basic anthropogenous sources: combustion of fuel in automobile engines (50 %) and on thermal power stations, burning of firm waste products, forest fires, and also manufacture of nitric acid, mineral fertilizers, artificial fibres, etc.
Nitrogen oxides in an atmosphere lead to formation of brown smog. It inflicts damages on health of people, ruins vegetation.
Nitrogen oxides in clouds and fogs incorporate with water, forming the drops of diluted nitric acid or salts. It leads to formation of acid rains.
Aerosols. The quantity of aerosol particles, getting in an atmosphere from natural sources, is estimated in 700-2200 million tons one year, from artificial sources - 185-415 million tons one year.
Processes of formation of aerosols are various. First of all there are crushing, grinding and dusting of firm substances. In the nature the mineral dust (dusty storms in deserts, volcanic ashes) has such origin. Sources of aerosols are also the technological processes of economic activities of people. A powerful source of a dust is the industry of building materials. A natural source of aerosols is an ocean. Aerosols in the form of chlorides and sulphates are formed as a result of evaporation of sea water and make 40 % of all aerosols getting in an atmosphere.
Aerosols are formed at condensation of substances, during burning or at incomplete combustion (soot). Such aerosols are formed at forest fires and burning of coal, oil, wood, waste products.
Aerosol pollutions. Aerosols influence on a weather and a climate. Small particles do an atmosphere muddy. Large particles are the centers of condensation of moisture, promote the formation of clouds and fogs, rains and snow. 1 milligram of aerosols settles in an organism of the inhabitant of the big city every day. It renders the big harm to health of people (bronchitis, asthma, allergic diseases, cancer lungs).
Heavy metals. Metals production is accompanied by emissions of such poisonous substances, as antimony, lead, arsenic, vapours of mercury, copper, zinc. Burning of fuel gives 85 % of vanadium emissions in an atmosphere, 98 - cobalt, 80 - antimony, 77 - nickel, 50 - selenium. Automobile exhausts deliver 250-300 thousand tons of lead annually.
Дата добавления: 2017-11-04; просмотров: 161;