Destruction of an ozone layer of the earth by chlorofluorocarbonses

In 1985 experts in research of atmosphere from the British Antarctic Service have reported about absolutely unexpected fact: the spring maintenance of ozone in atmosphere over station of Halley-beat in Antarctica has decreased from 1977 on 1984 for 40 %. Soon this conclusion was confirmed with other explorers who have shown also, that the range of the lowered maintenance of ozone is stretched for limens of Antarctica and on height covers a layer from 12 to 24 km, i.e. a considerable part of the inferior stratosphere. The international Plane Antarctic Ozone Experiment was the most detailed research of an ozone layer over Antarctica. In its course scientists from 4 countries some times rose in range of the lowered maintenance of ozone and have collected a detailed information on its dimensions and chemical processes driving in it. Actually it meant, that in polar atmosphere there is ozone "hole". In the beginning 80 on measurements from companion "Нимбус-7" the similar hole has been discovered and in Arctic regions, the truth it covered considerably the smaller area and falling of level of ozone in it was not so is great - about 9 %. On the average by the ground with 1979 on 1990 the ozone maintenance has fallen to 5 %.

This discovering has disturbed both scientists, and wide sociability as from it followed, that an ozone layer surrounding our planet, is in larger hazards, than was considered earlier. attenuation this layer can lead to serious consequences for mankind. The ozone maintenance in atmosphere less than 0.0001 %, however ozone completely absorbs a rigid ultraviolet radiation of the sun with length of a wave l <280 nanometers and considerably relaxs strip UVB with 280 <l <315 nanometers inflicting serious lesions to cages of alive organisms. Falling of concentration of ozone on 1 % leads on the average to augmentation of intensity of a rigid ultraviolet at an earth surface on 2 %. This estimation proves to be true the measurements spent in Antarctica (the truth, because of low position of the sun, intensity of an ultraviolet in Antarctica still more low, than in average widths. On the influence on alive organisms the rigid ultraviolet is close to ionising radiations, however, because of larger, than at g-radiation of length of a wave it is not capable to inpour deeply into fabrics and consequently amazes only surface members. The rigid ultraviolet possesses sufficient energy for destruction of DNA and other organic moleculas that can invoke a skin cancer, in particular swift-flowing malignant melanoma, a cataract and immune insufficiency. Naturally, rigid ultraviolet is capable to invoke and customary burns of a skin and a cornea. Already now all over the world the augmentation of number of disease by a skin cancer is appreciable, however the significant amount of other factors (for example, the increased popularity of sunburn leading to that people of more time spend on the sun, thus receiving big dose UV of an irradiating) does not allow to assert unequivocally, that in it reduction of the maintenance of ozone is guilty. The rigid ultraviolet is badly absorbed by water and consequently represents the big hazard to sea ecosystems. Experiments have shown, that the plankton dwelling in a near-surface layer at augmentation of intensity rigid UV can seriously suffer and even to be lost completely. The plankton is in the establishment of alimentary chains practically all sea ecosystems, therefore without exaggeration it is possible to tell, that practically all life in near-surface layers of the seas and oceans can disappear. Plants are less sensitive to rigid UV, but at dose augmentation can suffer and they.

If the ozone maintenance in atmosphere considerably decreases, the mankind will easily find a method to be protected from rigid UV radiances but thus risks to die of hunger.

Ozone formation is described by the equation of reaction O2+O?O3

Singlet oxygen necessary for this reaction above the level 20 km is formed at splitting of oxygen under the influence of an ultraviolet radiation with l <240 nanometers

O2+h0→2O

Below this level such photons do not make through almost, and atoms of oxygen are formed, basically, at nitrogen dioxide photodissociation

NO2+h0→NO+O

Photons of a soft ultraviolet with l <400 nanometers.

Destruction of molecules of ozone occurs at their hit on particles of aerosols or on an earth surface, but the basic outlet of ozone is defined by cycles of catalytic reactions in a gas phase:

O3+Y→YO+O2

YO+O→Y+O2

Where Y=NO, OH, Cl, Br

For the first time the thought on hazard of destruction of an ozone layer has been stated still in the late sixties then was considered, that the basic hazard to atmospheric ozone is represented by outbursts of steam and nitrogen oxides (NOx) from engines of supersonic transport planes and rockets. However, the supersonic aircraft developed much less rough rates, than it was supposed. Now in commercial objectives the "Concorde" making of some flights in week between America and Europe is used only, from military planes in a stratosphere supersonic strategic bombers, such as B1-B or Tu-160 and prospecting planes of type SR-71 fly practically only. Such loading hardly represents serious threat for an ozone layer. Outbursts of oxides of nitrogen from a surface of the earth as a result of burning of fossil fuel and quantity production and application of nitrogenous fertilizers also represents certain hazard to an ozone layer, but nitrogen oxides are unstable and easily collapse in atmosphere low layers. Starts of rockets also occur not so often, however, chlorate solid fuels used in modern space systems, for example in solid-fuel accelerators "Space-shuttles" or "Ariane", can cause a serious local damage to an ozone layer around start.

In 1974 Molina and Rowland from the Californian university in Irwin have shown, that chlorofluorocarbons (CFC) can cause ozone destruction. Since this time so-called chlorofluorocarbons the problem became one of the cores in researches on atmosphere pollution. Chlorofluorocarbons are more narrow more than 60 years froth-forming agents in fire extinguishers, purifying agents for electronic devices are used as refrigerants in coolers and conditioners, propellent for aerosol mixes, at clothes dry cleaning, by production polyfoams.

Once they were considered as ideal chemicals for practical application as they are very stable and inactive, so are not toxic. As it is paradoxical, but inertness of these connections does their dangerous to atmospheric ozone. CFC do not break up quickly in troposphere (low layer of atmosphere which is stretched from a surface of the earth to height of 10 km) as it occurs, for example, from mostly nitric oxides, and eventually make through into a stratosphere which high bound settles down at height about 50 km. When molecules CFC rise to height about 25 km where concentration of ozone is maximum, they are exposed to intensive influence of an ultraviolet radiation which does not make through on smaller heights because of ozone shadow effect. The ultraviolet destroys steady molecules in usual conditions CFC which break up to components possessing high reactivity, in particular nuclear chlorine. Thus CFC transfers chlorine from an earth surface through troposphere and atmosphere low layers where less inert connections of chlorine collapse, in a stratosphere, to bed with the greatest concentration of ozone. It is very important, that chlorine at ozone destruction operates like the catalyst: during chemical process its quantity does not decrease. Thereof one atom of chlorine can destroy to 100 000 molecules of ozone before will be deactivated or will return to troposphere. Now outburst CFC in atmosphere is estimated in millions tons, but it is necessary to notice, what even in a hypothetical case of complete phase-out and use CFC of immediate result to reach it will not be possible: action already got to atmosphere CFC will proceed some decades. It is considered, that life time in atmosphere for two most widely used CFC (CFCl3) and dichlorodifluoro methane (CF2Cl2) makes a trichloromonofluoromethane of 75 and 100 years accordingly.

Nitrogen oxides are capable destroy ozone, however, they can to react and with chlorine. For example:

O3+Cl → ClO+O2

ClO+NO→NO2+Cl

NO2→NO+O

O2+O→O3

During this reaction the ozone maintenance does not vary. More important is other reaction:

ClO+NO2→ClONO2

Nitrosyl chloride formed in its course is the so-called tank of chlorine. Chlorine containing in it is inactive and cannot enter reaction with ozone. Eventually such molecule-tank can capture a photon or enter reaction with any other molecule and liberate chlorine, but she also can leave a stratosphere. Calculations show, that if in a stratosphere there were no nitrogen oxides ozone destruction would go much faster. Other important tank of chlorine is hydrogen chloride HCl formed at reaction of singlet chlorine and methane СH4.

Under pressure these arguments many countries have started to take measures directed on curtailment of production and uses CFC. Since 1978 in the USA use CFC in aerosols was forbidden. Unfortunately, use CFC in other areas has not been limited. In September, 1987 of 23 leading countries of the world have signed in Montreal the convention obliging them to reduce consumption CFC. According to the reached arrangement the developed countries should reduce by 1999 consumption CFC to half of level of 1986 For use in quality propellent in aerosols quite good substitute CFC - propyl hydride-butanovaja a mix is already found. On physical parametres it practically does not concede to freons, but, unlike them, is inflammable. Nevertheless such aerosols are already manufactured in many countries, including in Russia. Business with a refrigerating machinery - the second-large consumer of freons more difficult is. The matter is that because of polarity of molecule CFC have high evaporation heat that is very important for a working body in coolers and conditioners. The best substitute of freons known for today is ammonia, but it is toxic and still concedes CFC on physical parametres. Quite good results are received for completely fluohydrocarbons. In many countries minings of new substitutes are conducted and quite good practical results, but completely this problem are already reached is not solved yet.

Use of freons proceeds and while is far even before stabilisation of level CFC in atmosphere. So, according to a network of Global monitoring of changes of a climate, in background conditions - on coast of Silent and Atlantic oceans and on islands, far from industrial and densely populated areas - concentration of freons-11 and-12 grows now with speed of 5-9 % in a year. The maintenance in a stratosphere of actinic connections of chlorine now in 2-3 times above in comparison with level of 50th years, prior to the beginning of fast production of freons.

At the same time, the early forecasts predicting, for example, that at preservation of modern level of outburst CFC, to the middle of XXI century the ozone maintenance in a stratosphere can fall twice, were probably too pessimistic. First, the hole over Antarctica in many respects is a consequence of meteorological processes. Ozone formation probably only in the presence of an ultraviolet and during polar night does not go. In the winter over Antarctic the steady whirlwind interfering inflow of air rich with ozone from averages width is formed. Therefore by the spring even the small amount of active chlorine capablly to cause a serious damage to an ozone layer. Such whirlwind practically is absent over Arctic regions, therefore in northern hemisphere falling of concentration of ozone is much less. Many researchers consider, that polar stratospheric clouds exercise influence over process of destruction of ozone. These high-rise clouds which are much more often observed over Antarctic, than over Arctic regions, are formed in the winter when in the absence of a sunlight and in the conditions of meteorological isolation of Antarctica the temperature in a stratosphere falls more low-80 °. It is possible to assume, that nitrogen connections condence, freeze and remain connected with cloudy particles and consequently possibility to enter reaction with chlorine lose. Probably also, that cloudy particles are capable to catalyze disintegration of ozone and chlorine tanks. All it means that CFC are capable to cause appreciable depressing of concentration of ozone only in specific atmospheric conditions of Antarctica, and for appreciable effect in centre widths, concentration of active chlorine should be much more above. Secondly, at ozone layer destruction the rigid ultraviolet will start to make through more penetrating into atmosphere. But it means, that ozone formation will occur still, but only little bit more low, in area to the big maintenance of oxygen. However, in this case the ozone layer in the big degree will be subject to action of atmospheric circulation.

Though the first gloomy estimations have been scraped, it at all does not mean, that the problem is not present. Became faster clearly, that there is no immediate serious hazard. Even the most optimistical estimations predict at modern level of outburst CFC in atmosphere serious biospheric failures in second half XXI century, therefore to reduce use CFC on former it is necessary.

Possibilities of influence of the person on the nature constantly grow and have already reached such level when probably to cause to biosphere an irreparable damage. Any more for the first time the substance, which long time was considered absolutely harmless, it appears actually the extremely dangerous. About twenty years ago hardly somebody could assume that the usual aerosol container can represent serious threat for a planet as a whole. Unfortunately, far not always it is possible to predict in time as this or that connection will attack biosphere. However in a case with CFC such possibility was: all chemical reactions describing process of destruction of ozone CFC are extremely simple and known for a long time. But even after problem CFC in 1974 has been formulated, the unique country which has taken any measures on curtailment of production CFC were the USA and these measures were absolutely insufficient. Serious enough demonstration of hazard CFC was required that serious measures on a global scale have been taken. It is necessary to notice, what even after ozone gap discovery, the confirmation of the Montreal convention one time was under the threat. Perhaps, problem CFC will learn with the big attention and hazard to concern all substances getting to biosphere as a result of activity of mankind.