Why and how the atmosphere is studied: the science of the armor of the Earth. Ozone shield A layer of the atmosphere that traps harmful ultraviolet rays

Atmosphere (from the Greek atmos - steam and spharia - a ball) - the air shell of the Earth, rotating with it. The development of the atmosphere was closely associated with the geological and geochemical processes taking place on our planet, as well as with the activities of living organisms.

The lower boundary of the atmosphere coincides with the surface of the Earth, since air penetrates into the smallest pores in the soil and is dissolved even in water.

The upper boundary at an altitude of 2000-3000 km gradually turns into space.

Thanks to the atmosphere, which contains oxygen, life on Earth is possible. Atmospheric oxygen is used in the process of respiration by humans, animals, and plants.

If there was no atmosphere, the earth would be as quiet as the moon. After all, sound is the vibration of air particles. The blue color of the sky is explained by the fact that the sun's rays, passing through the atmosphere, as through a lens, decompose into their constituent colors. At the same time, the rays of blue and blue colors are scattered most.

The atmosphere traps most of the sun's ultraviolet radiation, which has a detrimental effect on living organisms. It also keeps heat at the surface of the Earth, preventing our planet from cooling.

The structure of the atmosphere

Several layers can be distinguished in the atmosphere, differing in density and density (Fig. 1).

Troposphere

Troposphere - the lowest layer of the atmosphere, the thickness of which is 8-10 km above the poles, in temperate latitudes - 10-12 km, and above the equator - 16-18 km.

Figure: 1. The structure of the Earth's atmosphere

The air in the troposphere is heated from the earth's surface, that is, from land and water. Therefore, the air temperature in this layer decreases with height by an average of 0.6 ° C for every 100 m. At the upper border of the troposphere, it reaches -55 ° C. At the same time, in the equatorial region at the upper border of the troposphere, the air temperature is -70 ° C, and in the North Pole region -65 ° C.

In the troposphere, about 80% of the mass of the atmosphere is concentrated, almost all water vapor is located, thunderstorms, storms, clouds and precipitation occur, and vertical (convection) and horizontal (wind) air movement also occurs.

We can say that the weather is mainly formed in the troposphere.

Stratosphere

Stratosphere - the layer of the atmosphere located above the troposphere at an altitude of 8 to 50 km. The color of the sky in this layer appears purple, which is due to the rarefaction of the air, due to which the sun's rays are almost not scattered.

The stratosphere contains 20% of the mass of the atmosphere. The air in this layer is rarefied, there is practically no water vapor, and therefore almost no clouds and precipitation are formed. However, stable air currents are observed in the stratosphere, the speed of which reaches 300 km / h.

This layer is concentrated ozone (ozone screen, ozonosphere), a layer that absorbs ultraviolet rays, preventing them from reaching the Earth and thereby protecting living organisms on our planet. Thanks to ozone, the air temperature at the upper boundary of the stratosphere is in the range from -50 to 4-55 ° C.

Between the mesosphere and the stratosphere, there is a transition zone - the stratopause.

Mesosphere

Mesosphere - the layer of the atmosphere located at an altitude of 50-80 km. The air density here is 200 times less than at the Earth's surface. The color of the sky in the mesosphere appears to be black, stars are visible during the day. The air temperature drops to -75 (-90) ° С.

At an altitude of 80 km begins thermosphere. The air temperature in this layer rises sharply to a height of 250 m, and then becomes constant: at an altitude of 150 km it reaches 220-240 ° C; at an altitude of 500-600 km it exceeds 1500 ° C.

In the mesosphere and thermosphere, under the action of cosmic rays, gas molecules decay into charged (ionized) particles of atoms, therefore this part of the atmosphere is called ionosphere - a layer of very rarefied air, located at an altitude of 50 to 1000 km, consisting mainly of ionized oxygen atoms, nitrogen oxide molecules and free electrons. This layer is characterized by a high electrification, and long and medium radio waves are reflected from it, as from a mirror.

In the ionosphere, auroras arise - the glow of rarefied gases under the influence of electrically charged particles flying from the Sun - and sharp fluctuations of the magnetic field are observed.

Exosphere

Exosphere - the outer layer of the atmosphere, located above 1000 km. This layer is also called the scattering sphere, since gas particles move here at high speed and can be scattered into outer space.

Atmosphere composition

The atmosphere is a mixture of gases, consisting of nitrogen (78.08%), oxygen (20.95%), carbon dioxide (0.03%), argon (0.93%), a small amount of helium, neon, xenon, krypton (0.01%), ozone and other gases, but their content is negligible (Table 1). The modern composition of the Earth's air was established more than a hundred million years ago, but the sharply increased production activity of man still led to its change. Currently, there is an increase in CO 2 content by about 10-12%.

The gases in the atmosphere have different functional roles. However, the main significance of these gases is determined primarily by the fact that they very strongly absorb radiant energy and thus have a significant effect on the temperature regime of the Earth's surface and atmosphere.

Table 1. Chemical composition dry atmospheric air near the earth's surface

Nitrogen, the most widespread gas in the atmosphere, it is not chemically active.

Oxygen, unlike nitrogen, it is a very active chemical element. The specific function of oxygen is the oxidation of organic matter of heterotrophic organisms, rocks and under-oxidized gases emitted into the atmosphere by volcanoes. Without oxygen, there would be no decomposition of dead organic matter.

The role of carbon dioxide in the atmosphere is exceptionally great. It enters the atmosphere as a result of combustion processes, respiration of living organisms, decay and is, first of all, the main building material for creating organic matter during photosynthesis. In addition, the property of carbon dioxide is of great importance to transmit short-wave solar radiation and absorb some of the thermal long-wave radiation, which will create the so-called greenhouse effect, which will be discussed below.

The influence on atmospheric processes, especially on the thermal regime of the stratosphere, is also exerted by ozone. This gas serves as a natural absorber of ultraviolet radiation from the sun, and absorption of solar radiation leads to heating of the air. The average monthly values \u200b\u200bof the total ozone content in the atmosphere vary depending on the latitude of the area and the time of year within the range of 0.23-0.52 cm (this is the thickness of the ozone layer at ground pressure and temperature). An increase in ozone content from the equator to the poles and an annual variation with a minimum in autumn and maximum in spring are observed.

A characteristic property of the atmosphere is that the content of the main gases (nitrogen, oxygen, argon) changes insignificantly with height: at an altitude of 65 km in the atmosphere, the content of nitrogen is 86%, oxygen is 19, argon is 0.91, and at an altitude of 95 km - nitrogen 77, oxygen - 21.3, argon - 0.82%. The constancy of the composition of atmospheric air vertically and horizontally is maintained by mixing it.

In addition to gases, the air contains water vapor and solid particles. The latter can be of both natural and artificial (anthropogenic) origin. These are pollen, tiny salt crystals, road dust, aerosol impurities. When the sun's rays enter the window, they can be seen with the naked eye.

There are especially many solid particles in the air of cities and large industrial centers, where emissions of harmful gases and their impurities formed during fuel combustion are added to aerosols.

The concentration of aerosols in the atmosphere determines the transparency of the air, which affects the solar radiation reaching the Earth's surface. The largest aerosols are condensation nuclei (from lat. condensatio - compaction, thickening) - contribute to the transformation of water vapor into water droplets.

The value of water vapor is determined primarily by the fact that it delays the long-wave thermal radiation of the earth's surface; represents the main link of large and small moisture cycles; increases the air temperature during condensation of water beds.

The amount of water vapor in the atmosphere changes over time and space. Thus, the concentration of water vapor at the earth's surface ranges from 3% in the tropics to 2-10 (15)% in Antarctica.

The average content of water vapor in the vertical column of the atmosphere in temperate latitudes is about 1.6-1.7 cm (such a thickness will have a layer of condensed water vapor). Information on water vapor in different layers of the atmosphere is contradictory. It was assumed, for example, that in the altitude range from 20 to 30 km, the specific humidity increases strongly with height. However, subsequent measurements indicate a greater dryness of the stratosphere. Apparently, the specific humidity in the stratosphere depends little on the height and amounts to 2-4 mg / kg.

The variability of the content of water vapor in the troposphere is determined by the interaction of the processes of evaporation, condensation and horizontal transport. As a result of condensation of water vapor, clouds form and precipitation falls in the form of rain, hail and snow.

The processes of phase transitions of water occur mainly in the troposphere, which is why clouds in the stratosphere (at altitudes of 20-30 km) and in the mesosphere (near the mesopause), called mother-of-pearl and silvery, are observed relatively rarely, while tropospheric clouds often cover about 50% of the entire earth surface.

The amount of water vapor that can be contained in the air depends on the air temperature.

1 m 3 of air at a temperature of -20 ° C can contain no more than 1 g of water; at 0 ° С - no more than 5 g; at +10 ° С - no more than 9 g; at +30 ° С - no more than 30 g of water.

Output: the higher the air temperature, the more water vapor it can contain.

The air can be saturated and not saturated water vapor. So, if at a temperature of +30 ° C 1 m 3 of air contains 15 g of water vapor, the air is not saturated with water vapor; if 30 g is saturated.

Absolute humidity Is the amount of water vapor contained in 1 m 3 of air. It is expressed in grams. For example, if they say "the absolute humidity is 15", it means that 1 ml of L contains 15 g of water vapor.

Relative humidity Is the ratio (in percent) of the actual water vapor content in 1 m 3 of air to the amount of water vapor that can be contained in 1 ml L at a given temperature. For example, if the radio during the broadcast of the weather report says that the relative humidity is 70%, this means that the air contains 70% of the water vapor that it can hold at that temperature.

The higher the relative humidity of the air, i.e. the closer the air is to saturation, the more likely precipitation is.

Always high (up to 90%) relative humidity is observed in the equatorial zone, since there is a high air temperature throughout the year and there is a lot of evaporation from the surface of the oceans. The same high relative humidity and in the polar regions, but only because at low temperatures, even a small amount of water vapor makes the air saturated or close to saturation. In temperate latitudes, the relative humidity changes with the seasons - it is higher in winter and lower in summer.

Especially low relative air humidity in deserts: 1 m 1 of air there contains two to three times less water vapor possible at a given temperature.

To measure the relative humidity, a hygrometer is used (from the Greek hygros - wet and metreco - I measure).

When cooled, saturated air cannot retain the same amount of water vapor; it thickens (condenses), turning into fog droplets. Fog can be seen in the summer on a clear cool night.

The clouds - this is the same fog, only it is formed not near the earth's surface, but at a certain height. Rising up, the air is cooled, and the water vapor in it condenses. The resulting tiny droplets of water make up the clouds.

The formation of clouds involves and solid particlessuspended in the troposphere.

Clouds can have different shapes, which depend on the conditions of their formation (Table 14).

The lowest and heaviest clouds are stratus. They are located at an altitude of 2 km from the earth's surface. At an altitude of 2 to 8 km, more picturesque cumulus clouds can be observed. The highest and lightest are cirrus clouds. They are located at an altitude of 8 to 18 km above the earth's surface.

Protection of the atmosphere

The main source is industrial plants and automobiles. In big cities, the problem of gas pollution on the main transport routes is very acute. That is why in many large cities of the world, including in our country, environmental control of the toxicity of vehicle exhaust gases has been introduced. According to experts, smoke and dustiness of the air can halve the supply of solar energy to the earth's surface, which will lead to a change in natural conditions.

Currently, it is generally accepted that all life on Earth protects the ozone layer from the harmful effects of hard, biologically hazardous ultraviolet radiation. Therefore, the report that "holes" have been discovered in this layer - regions where the thickness of the ozone layer has been significantly reduced, caused considerable concern throughout the world. After a number of studies, it was concluded that the destruction of ozone is promoted by freons - fluorochlorine derivatives of saturated hydrocarbons (C n H 2n + 2), having chemical formulas such as CFCl 3, CHFCl 2, C 3 H 2 F 4 Cl 2 and others. Freons were already widely used by that time: they served as a working substance in domestic and industrial refrigerators, they charged aerosol cans with perfumes and household chemicals as a propellant (propellant gas), they were used to develop some technical photographic materials. And since the leaks of freons are colossal, the Vienna Convention for the Protection of the Ozone Layer was adopted in 1985, and on January 1, 1989, the International (Montreal) Protocol banning the production of freons was drawn up. Nevertheless, a senior researcher at one of the Moscow institutes N.I. Chugunov, a specialist in physical chemistry, a participant in the Soviet-American negotiations on the prohibition of chemical weapons (Geneva, 1976), had serious doubts as to the "merits" of ozone in protecting from ultraviolet radiation, and in the "fault" of freons in the destruction of the ozone layer.

The essence of the proposed hypothesis is that it is not ozone, but atmospheric oxygen, that protects all life on Earth from the biologically hazardous ultraviolet radiation. It is oxygen, by absorbing this short-wave radiation, that is converted into ozone. Let's consider the hypothesis from the point of view of the basic law of nature - the law of conservation of energy.

If, as is now commonly believed, the ozone layer traps ultraviolet radiation, then it absorbs its energy. But energy cannot disappear without a trace, and therefore something must happen to the ozone layer. There are several options.

Transition of radiation energy into heat. The consequence of this should be heating of the ozone layer. However, it is located at the height of a persistently cold atmosphere. And the first area of \u200b\u200bincreased temperature (the so-called mesopic) is more than two times higher than the ozone layer.

Ultraviolet energy is spent on ozone destruction. If so, not only the main thesis about the protective properties of the ozone layer collapses, but also the accusations against "insidious" industrial emissions that allegedly destroy it.

Accumulation of radiation energy in the ozone layer. It cannot go on forever. At some point, the limit of saturation of the ozone layer with energy will be reached, and then, most likely, an explosive chemical reaction will take place. However, in nature, no one has ever observed an explosion of the ozone layer.

The inconsistency with the law of conservation of energy indicates that the opinion about the absorption of hard ultraviolet radiation by the ozone layer is not substantiated.

It is known that ozone forms a layer of increased concentration at an altitude of 20-25 kilometers above the Earth. The question arises - where did he come from there? If we consider ozone as a gift of nature, then it is not suitable for this role - it decomposes too easily. Moreover, the decomposition process has the peculiarity that at a low ozone content in the atmosphere, the decomposition rate is low, but with an increase in concentration, it sharply increases, and at 20–40% of the ozone content in oxygen, decomposition is already explosive. And in order for ozone to appear in the air, the effect of some kind of energy source on atmospheric oxygen is necessary. It can be an electric discharge (a special "freshness" of the air after a thunderstorm is a consequence of the appearance of ozone), as well as short-wave ultraviolet radiation. It is the irradiation of air with ultraviolet light with a wavelength of about 200 nanometers (nm) that is one of the ways to obtain ozone in laboratory and industrial conditions.

Ultraviolet radiation from the Sun lies in the wavelength range from 10 to 400 nm. The shorter the wavelength, the more energy the radiation carries. Radiation energy is spent on excitation (transition to a higher energy level), dissociation (separation) and ionization (transformation into ions) of atmospheric gas molecules. Expending energy, radiation is weakened, or, otherwise, absorbed. This phenomenon is quantitatively characterized by the absorption coefficient. With decreasing wavelength, the absorption coefficient increases - radiation affects the substance more strongly.

It is customary to subdivide ultraviolet radiation into two ranges - near ultraviolet (wavelength 200-400 nm) and far, or vacuum (10-200 nm). We do not care about the fate of vacuum ultraviolet radiation - it is absorbed in the high layers of the atmosphere. It is he who is credited with creating the ionosphere. Attention should be paid to the lack of logic when considering the processes of energy absorption in the atmosphere - the far ultraviolet creates the ionosphere, and the near one does not create anything, the energy disappears without consequences. This is the case for the hypothesis of its absorption by the ozone layer. The proposed hypothesis eliminates this illogicality.

We are interested in the near ultraviolet, which penetrates the lower layers of the atmosphere, including the stratosphere, troposphere, and irradiates the Earth. On its way, radiation continues to change its spectral composition due to the absorption of short waves. No radiation with wavelengths shorter than 280 nm was detected at an altitude of 34 kilometers. The most biologically hazardous radiation is considered to be with wavelengths from 255 to 266 nm. It follows from this that destructive ultraviolet light is absorbed without reaching the ozone layer, that is, heights of 20-25 kilometers. And radiation with a minimum wavelength of 293 nm reaches the surface of the Earth, there is no danger
representing. Thus, the ozone layer does not take part in the absorption of biohazardous radiation.

Let's consider the most probable process of ozone formation in the atmosphere. When the energy of short-wave ultraviolet radiation is absorbed, some of the molecules are ionized, losing an electron and acquiring a positive charge, and some dissociate into two neutral atoms. A free electron, formed during ionization, combines with one of the atoms, forming a negative oxygen ion. Oppositely charged ions combine to form a neutral ozone molecule. At the same time, atoms and molecules, absorbing energy, move to the upper energy level, into an excited state. For an oxygen molecule, the excitation energy is 5.1 eV. The molecules are in an excited state for about 10 -8 seconds, after which, emitting a quantum of radiation, they decay (dissociate) into atoms.

In the process of ionization, oxygen has an advantage: it requires the least energy among all gases that make up the atmosphere - 12.5 eV (for water vapor - 13.2; carbon dioxide - 14.5; hydrogen - 15.4; nitrogen - 15.8 eV).

Thus, when ultraviolet radiation is absorbed in the atmosphere, a kind of mixture is formed, in which free electrons, neutral oxygen atoms, positive ions of oxygen molecules predominate, and when they interact, ozone is formed.

The interaction of ultraviolet radiation with oxygen occurs throughout the entire height of the atmosphere - there is information that in the mesosphere, at an altitude of 50 to 80 kilometers, the process of ozone formation is already observed, which continues in the stratosphere (from 15 to 50 km) and in the troposphere (up to 15 km ). At the same time, the upper layers of the atmosphere, in particular the mesosphere, are subject to such a strong effect of short-wave ultraviolet radiation that the molecules of all gases that make up the atmosphere ionize and disintegrate. Ozone that has just formed there cannot but decompose, especially since this requires almost the same energy as for oxygen molecules. Nevertheless, it is not completely destroyed - part of the ozone, which is 1.62 times heavier than air, sinks into the lower layers of the atmosphere to an altitude of 20-25 kilometers, where the density of the atmosphere (about 100 g / m 3) allows it to be, as it were, in equilibrium state. There, ozone molecules create a layer of increased concentration. At normal atmospheric pressure, the ozone layer would be 3-4 millimeters thick. It is almost impossible to imagine to what ultra-high temperatures such a low-power layer would have to heat up if it really absorbed almost all the energy of ultraviolet radiation.

At altitudes below 20-25 kilometers, ozone synthesis continues, as evidenced by the change in the wavelength of ultraviolet radiation from 280 nm at an altitude of 34 kilometers to 293 nm at the Earth's surface. The formed ozone, being unable to rise upward, remains in the troposphere. This determines the constant ozone content in the air of the surface layer in winter at a level of up to 2 . 10 -6%. In summer, the ozone concentration is 3-4 times higher, apparently due to the additional formation of ozone during lightning discharges.

Thus, atmospheric oxygen protects all life on Earth from hard ultraviolet radiation, while ozone turns out to be just a by-product of this process.

When it was discovered the appearance of "holes" in the ozone layer over the Antarctic in September-October and over the Arctic - roughly in January-March, doubts arose about the reliability of the hypothesis about the protective properties of ozone and its destruction by industrial emissions, since neither in Antarctica nor There is no production at the North Pole.

From the standpoint of the proposed hypothesis, the seasonality of the appearance of "holes" in the ozone layer is explained by the fact that in summer and autumn over Antarctica and in winter and spring over the North Pole the Earth's atmosphere is practically not exposed to ultraviolet radiation. The poles of the Earth during these periods are in the "shadow", above them there is no source of energy necessary for the formation of ozone.

LITERATURE

Mitra S.K. Upper atmosphere. - M., 1955.
Prokofieva I.A. Atmospheric ozone... - M .; L., 1951.

Atmosphere

The atmosphere is a mixture of various gases that surround the Earth. These gases provide life for all living organisms.
The atmosphere gives us air and protects us from the harmful effects of sunlight. Thanks to its mass and gravity, it is held around the planet. In addition, the layer of the atmosphere (about 480 km thick) serves as a shield against bombardment by meteors wandering in space.

What is atmosphere?
The atmosphere consists of a mixture of 10 different gases, mainly nitrogen (about 78%) and oxygen (21%). The remaining 1 percent is mainly argon plus small amounts of carbon dioxide, helium and neon. These gases are inert (they do not chemically react with other substances). Sulfur dioxide, ammonia, carbon monoxide, ozone (a gas related to oxygen) and water vapor also make up a tiny fraction of the atmosphere. Finally, the atmosphere contains pollutants such as gaseous pollutants, smoke particles, salt, dust and volcanic ash.

Higher and higher
This mixture of gases and tiny particulates is made up of four main layers: the troposphere, stratosphere, mesosphere, and thermosphere. The first layer - the troposphere - is the thinnest, ending at about 12 km above the ground. But even this ceiling is insurmountable for aircraft, which usually fly at an altitude of 9-11 km. This is the warmest layer because the sun's rays reflect off the earth's surface and heat the air. With distance from the earth, the air temperature drops to -55 ° C in the upper part of the troposphere.
Next comes the stratosphere, which extends to an altitude of about 50 km above the surface. At the top of the troposphere is the ozone layer. The temperature here is higher than in the troposphere, since ozone traps a significant part of the harmful ultraviolet radiation. However, environmentalists are concerned that pollutants are destroying this layer.
Above the stratosphere (50-70 km) is the mesosphere. Within the mesosphere, at a temperature of about -225 ° C, there is a mesopause - the coldest region of the atmosphere. It is so cold here that clouds of ice form, which can be observed late at night when the setting sun illuminates them from below.
Meteors flying towards Earth usually burn up in the mesosphere. Despite the fact that the air here is very thin, the friction that occurs when a meteor collides with oxygen molecules creates an ultra-high temperature.

At the edge of space
The last main layer of the atmosphere separating the Earth from space is called the thermosphere. It is located at an altitude of about 100 km from the earth's surface and consists of an ionosphere and a magnetosphere.
In the ionosphere, solar radiation causes ionization. This is where the particles get an electrical charge. As they sweep through the atmosphere, auroral lights can be observed at high altitude. In addition, the ionosphere reflects radio waves, enabling long-distance radio communications.
Above is the magnetosphere, which is the outer edge of the Earth's magnetic field. It acts like a giant magnet and protects the Earth by trapping high energy particles.
The thermosphere has the lowest density among all layers, the atmosphere gradually disappears and merges with outer space.

Wind and weather
Weather systems around the world are located in the troposphere. They arise as a result of the combined effect of solar radiation on the atmosphere and the rotation of the Earth. Air movement, known as wind, occurs when warm air masses rise upward, displaced by cold air masses. The air warms up most at the equator, where the sun is at its zenith, and gets colder as it approaches the poles.
The part of the atmosphere filled with life is called the biosphere. It stretches from bird's eye view to the surface and deep into the land and ocean. Within the boundaries of the biosphere, a delicate process of balancing plant and animal life takes place.
Animals consume oxygen and breathe out carbon dioxide, which green plants "absorb" through photosynthesis, using energy from sunlight to release oxygen into the air. This ensures a closed cycle on which the survival of all animals and plants depends.

Threat to the atmosphere
The atmosphere has allowed this natural balance to be maintained for hundreds of thousands of years, but now this source of life and protection is seriously threatened by the consequences of human activities: the greenhouse effect, global warming, air pollution, ozone depletion and acid rain.
As a result of world industrialization over the past 200 years, the gas balance of the atmosphere has been disrupted. The burning of fossil fuels (coal, oil, natural gas) led to colossal emissions of carbon dioxide and other gases, especially after the advent of cars in the late 19th century. Advances in agricultural technology have also led to an increase in the amount of methane and nitrogen oxides released into the atmosphere.

the greenhouse effect
These gases, already present in the atmosphere, trap the heat of sunlight reflected from the surface. If they were not there, the Earth would be so cold that the oceans would freeze and all living organisms would perish.
However, when the content of "greenhouse gases" increases due to air pollution, too much heat is trapped in the atmosphere, which leads to a warming climate around the world. As a result, in the last century alone, the average temperature on the planet has increased by half a degree Celsius. Scientists today predict further warming by about 1.5-4.5 ° C by the middle of this century.
It is estimated that over a billion people (about one fifth of the world's population) breathe air heavily contaminated with harmful gases today. Basically we are talking about carbon monoxide and sulfur dioxide. This has caused a sharp increase in the number of diseases of the chest and lungs, especially among children and the elderly.
The increasing number of people suffering from skin cancer is also alarming. This is the result of exposure to ultraviolet rays penetrating the depleted ozone layer.

Ozone holes
The ozone layer in the stratosphere protects us by absorbing the sun's ultraviolet rays. However, the widespread worldwide use of chlorine and fluorinated hydrocarbons (CFCs) used in aerosol cans and refrigerators, as well as many types of household chemicals and polystyrene, has led to the fact that as they rise up, these gases decompose and form chlorine, which, in its turn, destroys ozone.
Antarctica researchers first reported the phenomenon in 1985, when a hole in the ozone layer formed over part of the southern hemisphere. If this happens elsewhere on the planet, we will be exposed to more intense exposure to harmful radiation. In 1995, scientists reported the disturbing news of the emergence of an ozone hole over the Arctic and parts of Northern Europe.

Acid rain
Acid rain (including sulfuric and nitric acid) is produced by the reaction of sulfur dioxide and nitrogen oxides (industrial pollutants) with water vapor in the atmosphere. Plants and animals die in places where acid rain falls. There are cases when acid rain destroyed entire forests. Moreover, acid rain falls into lakes and rivers, spreading its harmful effects over large areas and killing even the smallest life forms.
Violations of the natural balance of the atmosphere are fraught with extremely negative consequences. It is assumed that the level of the World Ocean will rise as a result of global warming, this will lead to flooding of the lowlands of the land. Cities like London and New York can be hit by floods. This will entail numerous casualties, epidemics due to contamination of water resources. The rainfall map will change, and vast areas will experience drought, causing widespread famine. All this will have to pay with a huge number of human lives.

What else can you do?
Today, more and more people are thinking about environmental problems, and the governments of many countries around the world are paying close attention to environmental issues. Issues such as energy efficiency are being tackled on a global scale. If we use less electricity and travel a few kilometers less, we can reduce the amount of fossil fuels used to produce electricity, gasoline and diesel. Many countries are working on the use of alternative energy sources, including wind and solar energy. However, they will not soon be able to replace fossil fuels on a large scale.
Trees, like other plants, convert carbon dioxide to oxygen and play a vital role in regulating greenhouse gases in the atmosphere. In South America, colossal amounts of rainforest are being cut down. The destruction of millions of square kilometers of forest means the release of less oxygen into the atmosphere and the accumulation of more carbon dioxide, creating a heat trap effect.

World campaigns
Campaigns are under way around the world to convince the governments of the countries concerned to stop deforestation. In some countries, attempts are being made to restore the natural balance by encouraging and subsidizing the planting of trees.
However, we can no longer be sure of the purity of the air we breathe. Thanks to public pressure, the use of CFCs is being phased out and alternative chemicals are being used instead. And yet, the atmosphere is still in danger. It is necessary to ensure tight control over human actions in order to guarantee a "cloudless" future of our atmosphere.

Water, sun rays and oxygen contained in the earth's atmosphere are the main conditions for the emergence and factors that ensure the continuation of life on our planet. At the same time, it has long been proven that the spectrum and intensity of solar radiation in the cosmic vacuum are unchanged, and on Earth, the effect of ultraviolet radiation depends on many reasons: the time of the year, geographic location, altitude, thickness of the ozone layer, cloud cover and the level of concentration of natural and industrial impurities in the air.

What is ultraviolet rays

The sun emits rays in the ranges visible and invisible to the human eye. The invisible spectrum includes infrared and ultraviolet rays.

Infrared radiation is electromagnetic waves with a length of 7 to 14 nm, which carry a colossal flow of thermal energy to the Earth, and therefore they are often called thermal. The share of infrared rays in solar radiation is 40%.

Ultraviolet radiation is a spectrum of electromagnetic waves, the range of which is conventionally divided into near and far ultraviolet rays. Distant or vacuum rays are completely absorbed by the upper atmosphere. In terrestrial conditions, they are artificially generated only in vacuum chambers.

Near ultraviolet rays are divided into three sub-ranges:

• long - A (UVA) from 400 to 315 nm;
• average - B (UVB) from 315 to 280 nm;
• short - С (UVС) from 280 to 100 nm.

How is ultraviolet radiation measured? Today, there are many special devices, both for domestic and professional use, that allow you to measure the frequency, intensity and magnitude of the received dose of UV rays, and thereby assess their probable harm to the body.

Despite the fact that ultraviolet radiation in the composition of sunlight occupies only about 10%, it is thanks to its effect that a qualitative leap has occurred in the evolutionary development of life - the release of organisms from water to land.

Major sources of ultraviolet radiation

The main and natural source of ultraviolet radiation is of course the Sun. But man also learned to "produce ultraviolet light" with the help of special lamp devices:

• high-pressure mercury-quartz lamps operating in the general range of UV radiation - 100-400 nm;
• vital fluorescent lamps generating wavelengths from 280 to 380 nm, with a maximum emission peak between 310 and 320 nm;
• ozone and ozone-free (with quartz glass) bactericidal lamps, 80% of ultraviolet rays of which are at a length of 185 nm.

Both the ultraviolet radiation of the sun and artificial ultraviolet light have the ability to affect the chemical structure of cells of living organisms and plants, and at the moment, only a few species of bacteria are known that can do without it. For everyone else, the absence of ultraviolet radiation will lead to inevitable death.

So what is the real biological effect of ultraviolet rays, what is the benefit and is there any harm from ultraviolet radiation for humans?

The effect of ultraviolet rays on the human body

The most insidious ultraviolet radiation is shortwave ultraviolet radiation because it destroys all kinds of protein molecules.

So why is terrestrial life possible and continuing on our planet? What layer of the atmosphere traps harmful ultraviolet rays?

Living organisms are protected from hard ultraviolet radiation by the ozone layers of the stratosphere, which completely absorb the rays of this range, and they simply do not reach the Earth's surface.

Therefore, 95% of the total mass of solar ultraviolet radiation falls on long waves (A), and approximately 5% on medium waves (B). But here it is important to clarify. Despite the fact that there are much more long UV waves, and they have a high penetrating ability, affecting the reticular and papillary layers of the skin, it is 5% of medium waves that cannot penetrate beyond the epidermis have the greatest biological effect.

It is ultraviolet radiation of the middle range that intensely affects the skin, eyes, and also actively affects the work of the endocrine, central nervous and immune systems.

On the one hand, exposure to ultraviolet light can cause:

• severe sunburn of the skin - ultraviolet erythema;
• clouding of the lens, leading to blindness - cataract;
• skin cancer - melanoma.

In addition, ultraviolet rays have a mutagenic effect and cause malfunctions of the immune system, which become the cause of other oncological pathologies.

On the other hand, it is the action of ultraviolet radiation that has a significant impact on metabolic processes in the human body as a whole. The synthesis of melatonin and serotonin increases, the level of which has a positive effect on the functioning of the endocrine and central nervous system. Ultraviolet light activates the production of vitamin D, which is the main component for the absorption of calcium, and also prevents the development of rickets and osteoporosis.

Irradiation of skin with ultraviolet light

Skin lesions can be both structural and functional in nature, which, in turn, can be divided into:

1. Sharp injuries - arise due to high doses of solar radiation of the rays of the middle range, received in this case in a short time. These include acute photodermatosis and erythema.
2. Delayed damage - arise against the background of prolonged exposure to long-wave ultraviolet rays, the intensity of which, by the way, does not depend on the season or daylight hours. These include chronic photodermatitis, photoaging of the skin or solar geroderma, ultraviolet mutagenesis and the onset of neoplasms: melanoma, squamous and basal cell skin cancer. Herpes is among the list of delayed injuries.

It is important to note that both acute and delayed injuries can be obtained with excessive enthusiasm for artificial sunbathing, not wearing sunglasses, as well as when visiting tanning salons using uncertified equipment and / or not conducting special preventive calibration of ultraviolet lamps.

UV protection of the skin

If you do not abuse any "sunbathing", then the human body will cope with the protection from radiation on its own, because more than 20% is retained by a healthy epidermis. Today, protection against ultraviolet radiation of the skin comes down to the following techniques that minimize the risk of malignant neoplasms:

• limiting the time spent in the sun, especially in the midday summer hours;
• wearing light but closed clothing, because to get the required dose that stimulates the production of vitamin D, it is not at all necessary to be covered with a tan;
• selection of sunscreens depending on the specific ultraviolet index characteristic of the area, time of year and day, as well as on your own skin type.

Attention! For indigenous people middle band In Russia, the UV index is above 8, not only requires the use of active protection, but also poses a real threat to health. Radiation measurements and solar index forecasts can be found on leading weather sites.

Exposure to UV light on the eyes

Damage to the structure of the ocular cornea and lens (electrophthalmia) is possible through eye contact with any source of ultraviolet radiation. Despite the fact that a healthy cornea does not transmit and reflects hard ultraviolet light by 70%, there are many reasons that can become a source of serious diseases. Among them:

• unprotected observation of flares, solar eclipses;
• a casual glance at a luminary on the sea coast or in high mountains;
• photo-injury from camera flash;
• monitoring the operation of the welding machine or neglect of safety precautions (lack of a protective helmet) when working with it;
• long-term operation of the strobe at discos;
• violation of the rules for visiting the solarium;
• long-term stay in a room in which quartz germicidal ozone lamps work.

What are the first signs of electrophthalmia? Clinical symptoms, namely redness of the sclera of the eye and eyelids, pain syndrome when moving the eyeballs and sensation of a foreign body in the eye, usually occur 5-10 hours after the above circumstances. Nevertheless, UV protection is available to everyone, because even ordinary glass lenses do not transmit most of the UV rays.

The use of protective glasses with a special photochromic coating on the lenses, the so-called "chameleon glasses", will be the optimal "household" option for eye protection. You don’t have to bother asking what color and shade the UV filter actually provides effective protection in your specific circumstances.

And of course, in case of expected eye contact with flashes of ultraviolet radiation, it is necessary to put on goggles in advance or use other devices that delay the rays that are harmful to the cornea and lens.

The use of ultraviolet radiation in medicine

Ultraviolet light kills fungus and other microbes in the air and on the surfaces of walls, ceilings, floors and objects, and after exposure to special lamps, mold is removed. People use this bactericidal property of ultraviolet radiation to ensure the sterility of manipulation and surgical premises. But ultraviolet radiation in medicine is used not only to fight nosocomial infections.

The properties of ultraviolet radiation have found their application in a wide variety of diseases. At the same time, new techniques arise and are constantly being improved. For example, ultraviolet blood irradiation, invented about 50 years ago, was originally used to suppress the growth of bacteria in the blood during sepsis, severe pneumonia, extensive purulent wounds and other purulent-septic pathologies.

Today, ultraviolet irradiation of blood or blood purification helps fight acute poisoning, drug overdose, furunculosis, destructive pancreatitis, obliterating atherosclerosis, ischemia, cerebral atherosclerosis, alcoholism, drug addiction, acute mental disorders, and many other .

Diseases for which the use of ultraviolet radiation is indicated, and when any procedure with UV rays is harmful:

In order to live without pain, for people with joint damage, an ultraviolet lamp will bring invaluable assistance in the general complex therapy.

The influence of ultraviolet radiation in rheumatoid arthritis and arthrosis, the combination of the ultraviolet therapy technique with the correct selection of the biodose and a competent antibiotic regimen is a 100% guarantee of achieving a systemic healing effect with minimal drug load.

In conclusion, we note that the positive effect of ultraviolet radiation on the body and just one single procedure for ultraviolet irradiation (purification) of the blood + 2 sessions in a solarium will help a healthy person look and feel 10 years younger.

The ozone screen is the layer of the atmosphere with the highest concentration of ozone molecules Oz at an altitude of about 20-25 km, absorbing hard ultraviolet radiation, which is fatal to organisms. Destruction of the o.e. as a result of anthropogenic pollution of the atmosphere, it poses a threat to all living things, and above all to humans.
The ozone screen (ozonosphere) is a layer of the atmosphere within the stratosphere, located at different heights from the Earth's surface and having the highest density (concentration of molecules) of ozone at an altitude of 22 - 26 km.
The ozone screen is a part of the atmosphere where ozone is found in a small concentration.
The content of nitrates in crop products. The destruction of the ozone screen is associated with nitrogen oxide, which serves as a source of formation of other oxides that catalyze the photochemical reaction of the decomposition of ozone molecules.
The emergence of the ozone screen, which fenced off the Earth's surface from chemically active radiation penetrating outer space, dramatically changed the course of the evolution of living matter. Under the conditions of the protobiosphere (primary biosphere), mutagenesis had a very intense character: all new forms of living matter emerged and varied rapidly, and gene pools were rapidly accumulating.
The ozonosphere (ozone screen), which lies above the biosphere, in a layer from 20 to 35 km, absorbing ultraviolet radiation, which is fatal for living beings of the biosphere, is formed due to oxygen, which is biogenic in origin, i.e. also created by the living matter of the Earth. However, even if living matter penetrates these layers in the form of spores or aeroplankton, then it does not reproduce in them and its concentration is negligible. Note that, penetrating into this shell of the Earth and even higher, into space, a person takes with him into the spaceship, as it were, a particle of the biosphere, i.e. the entire life support system.
Explain how the ozone screen is formed and what leads to its destruction.
The biosphere extends from the ozone screen, where bacterial and fungal spores meet at an altitude of 20 km, to a depth of more than 3 km below the earth's surface and about 2 km below the ocean floor. There, in the waters of oil fields, anaerobic bacteria are found. The largest concentration of biomass is concentrated at the boundaries of the geosphere, i.e. in coastal and surface ocean waters and on land surfaces. This is explained by the fact that the source of energy of the biosphere is sunlight, and autotrophic, and behind them and heterotrophic organisms, mainly populate places where solar radiation is most intense.
The most dangerous consequences for humans and many animals of the depletion of the ozone screen is an increase in the number of skin cancer and eye cataracts. In turn, this, according to official UN data, leads to the appearance in the world of 100 thousand new cases of cataracts and 10 thousand cases of skin cancer, as well as a decrease in immunity in both humans and animals.
The wall of environmental prohibitions, which has reached a global level (destruction of the ozone screen, acidification of precipitation, climate change, and so on), was not the only factor in social development. Simultaneously and in parallel, the economic structure has changed.
Dynamics of the ozone hole within Antarctica (according to N.F. Reimers, 1990 (space without shading. Extremely dangerous for humans and many animals consequences of ozone screen depletion - an increase in the number of skin cancer and eye cataracts). In turn, this, according to the official According to the UN, leads to the appearance in the world of 100 thousand new cases of cataracts and 10 thousand cases of skin cancer, as well as a decrease in immunity in both humans and animals.
Roughly the same thing happened with the growth in the production of freons, their impact on the ozone screen of the planet.
We have already said that life is preserved because an ozone screen has formed around the planet, which protected the biosphere from deadly ultraviolet rays. But in recent decades, a decrease in the ozone content in the protective layer has been noted.

As a result of photosynthesis, more and more oxygen began to appear in the atmosphere, and an ozone screen was formed around the planet, which became a reliable protection for organisms from the harmful ultraviolet radiation of the sun and short-wave cosmic radiation. Life began to flourish under its protection: plants suspended in water (phytoplankton), emitting oxygen, began to develop in the surface layers of the ocean. From ocean-n-a, organic life moved to land; the first living things began to inhabit the earth about 400 million years ago. Organisms that develop on earth and are capable of photosynthesis (plants) have further increased the flow of oxygen into the atmosphere. It is believed that it took at least half a billion years for the oxygen content in the atmosphere to reach its present level, which has not changed for about 50 million years.
But the high cost of such flights has slowed down the development of supersonic transportation so much that now they do not pose a significant threat to the ozone shield.
Global monitoring is carried out in order to obtain information about the biosphere as a whole or about individual biospheric processes, in particular, climate change, the state of the ozone screen, etc. The specific goals of global monitoring, as well as its objects, are determined in the course of international cooperation in the framework of various international agreements and declarations.
Global monitoring - tracking general processes and phenomena, including anthropogenic impacts on the biosphere, and warning of emerging extreme situations, such as the weakening of the planet's ozone screen, and other phenomena in the Earth's ecosphere.
The shortest wavelength (200 - 280 nm) zone of this part of the spectrum (ultraviolet C) is actively absorbed by the skin; in terms of danger, UV-C is close to JT rays, but is almost completely absorbed by the ozone shield.
The emergence of plants on land, apparently, was associated with the achievement of oxygen content in the atmosphere of about 10% of the present. The ozone shield was now able to at least partially protect organisms from ultraviolet radiation.
The destruction of the Earth's ozone screen is accompanied by a number of dangerous explicit and latent negative impacts on humans and wildlife.
At the upper boundary of the troposphere, ozone is formed from oxygen under the influence of cosmic radiation. Consequently, the ozone screen, which protects life from lethal radiation, is also the result of the activity of the living substance itself.
Natural conditions are not directly involved in material production, and non-production. Earth, the planet's ozone screen, protecting all life from cosmic. Many natural conditions produce with development, forces pass into the category of resources, so the border between these concepts is conditional.
The lower boundary of the biosphere runs at a depth of 3 km on land and 2 km below the ocean floor. The upper limit is the ozone screen, above which the sun's UV radiation excludes organic life. The basis of organic life is carbon.
Microorganisms have been found at this depth in the oil-bearing waters. The upper boundary is a protective ozone shield, which protects living organisms on Earth from the harmful effects of ultraviolet rays. Man also belongs to the biosphere.
What are the mechanisms of the retention of the ozonosphere as a layer in the stratosphere with the highest ozone density at heights of 22-25 km above the Earth's surface is not yet entirely clear. If the human impact on the ozone screen is limited to chemicals, then the protection of the ozonosphere from destruction is quite realistic by prohibiting chlorofluorocarbons and other chemical agents hazardous to it. If the thinning of the ozonosphere is associated with a change in the Earth's magnetic field, as some researchers suggest, then it is necessary to establish the reasons for this change.
In fact, as we can see, the geographic shell includes the earth's crust, atmosphere, hydrosphere and biosphere. Borders geographic envelope are determined from above by the ozone screen, and from below - by the earth's crust: under the continents at a depth of 30 - 40 km (including under the mountains - up to 70 - 80 km), and under the oceans - 5 - 8 km.
In most cases, the ozone layer is indicated as the upper theoretical boundary of the biosphere without specifying its boundaries, which is quite acceptable if the difference between the neo - and paleobiosphere is not discussed. Otherwise, it should be borne in mind that the ozone screen was formed only about 600 million years ago, after which the organisms were able to go to land.

Regulatory processes in the biosphere are also based on the high activity of living matter. Thus, the production of oxygen maintains the ozone screen and, as a consequence, the relative constancy of the flow of radiant energy reaching the planet's surface. The constancy of the mineral composition of oceanic waters is supported by the activity of organisms actively extracting individual elements, which balances their inflow with river runoff entering the ocean. Similar regulation is carried out in many other processes.
Nuclear explosions have a destructive effect on the stratospheric ozone screen, which is known to protect living organisms from the destructive effects of short-wave ultraviolet radiation.
To preserve the Earth's ozone layer, measures are being taken to reduce freon emissions and replace them with environmentally friendly substances. The current solution to the problem of preserving the ozone shield and destroying ozone holes necessary for the preservation of earthly civilization. At the UN Conference on Environment and Development, held in Rio de Janeiro, it was concluded that our atmosphere is increasingly affected by greenhouse gases that threaten climate change and chemicals that reduce the ozone layer.
In the upper layers of the stratosphere, ozone is located in a small concentration. Therefore, this part of the atmosphere is often referred to as the ozone shield. Ozone plays an important role in the formation of the temperature regime of the underlying layers of the atmosphere and, consequently, air currents. The ozone content is not the same over different parts of the earth's surface and at different times of the year.
The biosphere is the planetary envelope of the Earth, where life exists. In the atmosphere, the upper limits of life are determined by the ozone screen - a thin layer of ozone at an altitude of 16 - 20 km. Ocean is full of life entirely. The biosphere is a global ecosystem, supported by the biological circulation of matter and solar energy flows. All ecosystems of the Earth are all components.
Ozone O3 is a gas whose molecule consists of three oxygen atoms. An active oxidizing agent capable of destroying pathogens; an ozone shield in the upper atmosphere protects our planet from the sun's ultraviolet radiation.
The gradual increase in COL in the atmosphere, which is taking place today, associated with industrial emissions, may be the cause of the increase in the greenhouse effect and climate warming. At the same time, the currently observed partial destruction of the ozone screen can compensate to a certain extent for this effect by increasing heat loss from the Earth's surface. At the same time, the flux of short-wave ultraviolet radiation will increase, which is dangerous for many living organisms. As you can see, anthropogenic interference with the structure of the atmosphere is fraught with unpredictable and undesirable consequences.
Hydrocarbons in oil and gas are practically harmless, but, released when using fossil fuels, they accumulate in the atmosphere, water, soil and turn out to be causative agents of dangerous diseases. The production and massive release of freons into the atmosphere can destroy the protective ozone shield.
Let us consider the most typical consequences of human air pollution. Typical consequences are acid precipitation, greenhouse effect, ozone shield disruption, dust and aerosol pollution from large industrial centers.
Ozone is constantly being generated in the upper atmosphere. It is believed that at an altitude of about 25-30 km ozone forms a powerful ozone screen, which traps the bulk of ultraviolet rays, protecting organisms from their destructive effects. Together with carbon dioxide of the air and water vapor, it protects the Earth from hypothermia, delays the long-wave infrared (thermal) radiation of our planet.
Suffice it to say that oxygen in our atmosphere, without which life is impossible, the ozone screen, the absence of which would ruin earthly life, the soil cover on which all the vegetation of the planet develops, coal deposits and oil deposits - all this is the result of long-term activity of living organisms.
In the practice of agriculture, up to 30 - 50% of all applied mineral fertilizers are uselessly lost. The release of nitrogen oxides into the atmosphere entails not only economic losses, but also threatens to disrupt the planet's ozone screen.
Converted enterprises should be aimed at the design, production and implementation of ultra-modern technological systems for the production of civilian products at the level of world standards and mass demand. Only specialized scientific institutions and military-industrial complex plants are able to solve, for example, the most important task of replacing freons, which destroy the Earth's ozone screen, with other environmentally safer refrigerants.
The upper limit of life in the atmosphere is determined by the level of UV radiation. At an altitude of 25-30 km, most of the sun's ultraviolet radiation is absorbed by a relatively thin layer of ozone located here - the ozone screen. If living organisms rise above the protective ozone layer, they die. The atmosphere above the Earth's surface is saturated with a variety of living organisms that move in the air in an active or passive way. Spores of bacteria and fungi are found up to an altitude of 20 - 22 km, but the bulk of the air plankton is concentrated in a layer up to 1 - 15 km.
It is assumed that global pollution of the atmosphere by certain substances (freons, nitrogen oxides, etc.) may disrupt the functioning of the ozone screen.

OZONOSPHERE OZONE SCREEN - a layer of the atmosphere that closely coincides with the stratosphere, lying between 7 - 8 (at the poles), 17 - 18 (at the equator) and 50 km (with the highest ozone density at altitudes of 20 - 22 km) above the planet's surface and characterized by an increased concentration of ozone molecules, reflecting hard cosmic radiation, fatal to living things. It is assumed that global pollution of the atmosphere by some substances (freons, nitrogen oxides, etc.) may disrupt the functioning of the ozone screen.
The ozone layer effectively absorbs electromagnetic radiation with wavelengths in the range of 220 - 300 nm, acting as a shield. Thus, UV with a wavelength of up to 220 nm is completely absorbed by atmospheric oxygen molecules, and in the region of 220 - 300 nm it is effectively delayed by the ozone screen. An important part of the solar spectrum is the region adjacent on both sides to 300 nm.
The photodissociation process also underlies the formation of ozone from molecular oxygen. The ozone layer is located at an altitude of 10 - 100 km; the maximum ozone concentration is recorded at an altitude of about 20 km. The ozone screen is of great importance for the preservation of life on Earth: the ozone layer absorbs most of the ultraviolet radiation coming from the Sun, moreover, in its short-wavelength part, which is most destructive for living organisms. Only the soft part of the flux of ultraviolet rays with a wavelength of about 300 - 400 nm reaches the Earth's surface, which are relatively harmless, and according to a number of parameters are necessary for the normal development and functioning of living organisms. On this basis, some scientists draw the boundary of the biosphere precisely at the height of the ozone layer.
An evolutionary factor is a modern environmental factor generated by the evolution of life. So, for example, the ozone screen - a current environmental factor that affects organisms, populations, biocenoses, ecological systems, including the biosphere - existed in past geological epochs. The appearance of the ozone screen is associated with the appearance of photosynthesis and the accumulation of oxygen in the atmosphere.
Another limiting factor for the upward penetration of life is hard cosmic radiation. At an altitude of 22-24 km from the Earth's surface, the maximum concentration of ozone is observed - the ozone screen. The ozone screen reflects cosmic radiation (gamma and X-rays) and partially ultraviolet rays that are destructive for living organisms.
Biological effects caused by radiation of different wavelengths. The most important source of natural radiation is solar radiation. The bulk of the solar energy incident on the Earth (about 75%) is accounted for by visible rays, almost 20% - in the infrared region of the spectrum, and only about 5% - in UV with a wavelength of 300 - 380 nm. The lower limit of the wavelengths of solar radiation incident on the earth's surface is determined by the density of the so-called ozone shield.