Ozone layer depletion - class-XI

'Good ozone' is found in the upper part of the atmosphere called the stratosphere and it act as a shield by absorbing ultraviolet radiations from the sun. UV rays are, highly injurious to living organisms. 'Bad ozone' is formed in the lower part of atmosphere called troposphere and it harms plants and animals.

Ozone-depleting substances (ODS) are substances that react with ozone present in the stratosphere and destroy the same. The major Ozone-depleting substances are chlorofluorocarbons (14% of total depletion), nitrogen oxides (3.5% depletion), sulphur dioxide, halon, carbon tetrachloride, methyl chloroform, chlorine, etc.

Ozone depletion is occurring widely in the stratosphere, particularly marked over the Antarctic region.

Ozone depletion occurs widely in the stratosphere due to an increased amount of $ { CFC }{ s } $ which causes various types of skin cancer and mutations.

An ozone layer, present in the stratosphere, reflects the ultraviolet rays emitted by the sun and thus it prevents us from skin diseases and mutation.

The main factor responsible for the depletion of ozone layer is addition of Cl in the atmosphere.
Each Cl atom can destroy as many as 100,000 ozone molecules. Cl atoms comes from chlorofluorocarbons.

The depletion of the ozone layer was noticed in the year 1980.
The large scale destruction of the stratospheric ozone first came into focus in 1987 through the experiments in antarctica.

Maximum threat to the world is from ozone layer which is found in the stratosphere. This layer acts as a shield absorbing UV radiations from the sun. For the ozone layer to be intact there has to be a balance between the production and degradation which has been disturbed by the CFCs used in refrigerators. The F and Cl, which are released by these compounds results in the thinning out of the ozone layer also known as the ozone hole. It causes threat to life and environment as it leads to skin aging and cancers, snow blindness, cataract, melting of polar ice caps, global warming etc.

The UV radiations can cause mutation in the cells by altering the DNA. These are ionising radiations which can damage the structure of the DNA molecule. The UV rays can result in the formation of thymine dimers or split the hydrogen bonding. This results in distortion in the structure of DNA and the cell dies due to malfunctioning of the genetic material. 

When the destruction of the ozone layer increases, the amount of harmful ultraviolet radiation increases.
Note:
Ozone layer acts as natural sun block and shields us from the UV radiations of the sun which are dangerous to living organisms.
The ozone molecules absorb ultraviolet rays between 310 to 200 nm wavelength.
Ozone absorbs UV radiation to give back oxygen. Thus, the ozone layer acts as a screen and prevents the harmful radiations from reaching the surface of earth.

The ultraviolet radiations are the harmful rays which are present in the sun rays. The radiations are emitted from the sun and are harmful to living organisms. The ozone layer prevents the entry of these radiations into the Earth's atmosphere. The depletion of the ozone layer allows the radiations to cause harm to the plants and animals on the Earth.

The presence of CFCs in the atmosphere results in the depletion of the ozone layer. They are used as coolants in refrigerators, coolers, etc. The CFCs causes the breaking of the ozone molecule which forms the oxygen radical and O$ _2$. The depletion of the ozone layer results in the penetration of the harmful UV radiations from the sun into the Earth's atmosphere. The reduction in the use of the CFC molecules will prevent the ozone thinning and have the positive effect on the ozone layer. 

Thinning of ozone layer increases the amount of ultraviolet radiations reaching the earth surface. The increased UV-B radiation increases incidence of cataract, skin cancers herpes, dimming of eyesight, photo burning, snow blindness and deficient functioning of immune system. 

• Ozone depletion occurs when chlorofluorocarbons (CFCs) present in aerosols and refrigerants are released into the stratosphere. 
• Ultraviolet radiations from the sun break these CFCs molecules and release the chlorine atoms.
• Chlorine atom reacts with the ozone (O₃) molecules and starts the ozone destruction cycle.
• So, the correct answer is 'Chlorofluorocarbons'.

Ozone gas is found in the stratosphere of the atmosphere. The ozone layer protects the earth from the harmful ultraviolet rays emitted from the sun. Ozone layer depletion has many adverse serious environmental effects. It may result in global warming. The ultraviolet radiations exposure leads to skin cancer like malignant melanoma. It also increases the rate of ageing in an individual. It also has harmful effect on the eyes. It may cause cataract. Immune system is also affected by this harmful ultraviolet radiations. Apart from humans, ozone layer depletion affects marine, aquatic and other forms of life as well.

• The ozone layer or ozone($O _3$) shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet(UV)radiation.
• Overexposure to UV radiation may cause skin cancer, damage of the eye and the suppression of the immune system.
  
• Hence The harmful radiations are absorbed by ozone layer UV.
• So, the correct answer is 'UV'.

Ozone is an inorganic molecule and a light blue gas with a pungent odor that is prevalent in the stratosphere just below the atmosphere of the earth. Without ozone, plants and animals would be receiving so much radiation from the sun that it would be difficult, if not impossible, for life to even survive here. The effects of no ozone to protect these harmful rays would be that all life here on earth would soon burn up, essentially. Although most associated with the atmosphere, ozone is also a powerful oxidant with many industrial and consumer uses. However, it must be used with extreme caution. The high oxidizing potential of ozone causes damage to mucous and respiratory tissues in animals and also damages tissue in plants at extremely high levels. In commercial agriculture, ozone can be used in conjunction with other chemicals and gases as a control for certain noxious weeds or pests.

Germany is widely recognized for its early and proactive implementation of policies to phase out ozone-depleting substances like CFCs and HCFCs. They were among the first to comply with international protocols.

Ozone depletion allows more harmful UV radiation to reach the Earth, which can lead to skin cancer and other health issues, and it also impacts global climate patterns. Therefore, all listed effects are correct.

Chlorofluorocarbons (CFCs) are the primary chemicals responsible for the depletion of the ozone layer. They release chlorine atoms when exposed to UV radiation in the stratosphere.

Chlorine and bromine atoms are the active agents that destroy ozone molecules. While CFCs are the source, the gases involved in the actual chemical reaction are chlorine and bromine.

The ozone layer protects the Earth by absorbing harmful ultraviolet (UV) radiation from the sun. Depletion of this layer leads to increased exposure to these radiations.

HCFCs (Hydrochlorofluorocarbons) were developed as transitional substitutes for CFCs (Chlorofluorocarbons) because they have a lower ozone depletion potential, though they are still harmful.

Hydrocarbons (HCs) are generally susceptible to oxidation reactions, especially in the presence of oxygen or oxidizing agents, which is why they are not thermodynamically stable in such environments.

Butane and other hydrocarbons like isobutane are commonly used as eco-friendly alternatives to CFCs in modern refrigeration systems because they have zero ozone depletion potential.

Ozone is the protective layer present in the stratosphere. The harmful ultraviolet radiation is absorbed by the ozone layer. They are carried high into the stratosphere by wind action. Depletion begins when CFC’s get into the stratosphere. Ultraviolet radiation from the sun breaks up these CFCs. The breaking up action releases chlorine atoms. Chlorine atoms react with ozone, starting a chemical cycle that destroys the good ozone in that area. It is not depleted by PCB, carbon monoxides, and PAN. 

Pollution leads to the addition of harmful components in the environment which adversely affect the quality of the environment. CFCs is an organic compound and a volatile derivative of methane, ethane, and propane. It is known as Freon. They are used as a refrigerant. The radical chlorine escapes from CFC in the presence of UV radiation and is long lived in the upper atmosphere where it catalyzes the conversion of ozone into oxygen molecule.

The ozone layer is mainly found in the stratosphere. Ozone layer acts as a shield that absorbs ultraviolet radiation from the sun. UV rays are highly injurious to living organisms since DNA and proteins of living organisms preferentially absorb UV rays, and its high energy breaks the chemical bonds within these molecules. UV-B damages DNA and mutation may occur. It causes aging of the skin, damage to skin cells and various types of skin cancers.

Ozone gas is a layer which is present in the stratosphere and absorbs the harmful ultraviolet radiation. The ozone depletion takes due to the excessive emission of (CFCs). CFC find wide use as refrigerants. CFCs discharged in the lower part of atmosphere move upward and reach stratosphere. In stratosphere, UV rays act on them releasing Cl atoms. Cl degrades ozone releasing molecular oxygen, with these atoms acting merely as catalysts; Cl atoms are not consumed in the reaction. Hence, whatever CFCs are added to the stratosphere, they have permanent and continuing affects on ozone levels. This has resulted in formation of a large area of thinned ozone layer, commonly called as the ozone hole.

Chlorofluorocarbons (Freons) release chlorine radicals in the stratosphere, which react with and destroy ozone (O3) molecules, leading to the depletion of the ozone layer.

The presence of CFCs in the atmosphere results in the depletion of the ozone layer. They are used as coolants in refrigerators, coolers, etc. The CFCs causes the breaking of the ozone molecule which forms the oxygen radical and O$ _2$. The depletion of the ozone layer results in the penetration of the harmful UV radiations from the sun into the Earth's atmosphere. 

Chlorofluorocarbons are the compounds which are used as coolants in the air conditioning systems, refrigerators, coolers, etc. The CFCs, when released into the atmosphere, react with UV rays to form chlorine atoms which destroy the ozone layer and results in the thinning out of the ozone layer also known as the ozone hole.

The ozone layer is present in the stratosphere above the Earth. The layer of ozone is responsible for the absorption of the harmful ultraviolet radiations from the solar radiations. Due to ozone depletion, these radiations enter the Earth's atmosphere and cause skin cancer. The radiations can also damage the eye and other exposed parts of the body. The radiations can also cause mutations like thymine dimer formation or breaking of the hydrogen bonds. 

Chlorofluorocarbon compounds are released from automobiles, refrigerators, etc. These compounds cause an increase in atmospheric temperature causing global warming.

The presence of CFCs in the atmosphere results in the depletion of the ozone layer. They are used as coolants in refrigerators, coolers, etc. The CFCs causes the breaking of the ozone molecule which forms the oxygen radical and O$ _2$. The depletion of the ozone layer results in the penetration of the harmful UV radiations from the sun into the Earth's atmosphere. 

Ozone is an inorganic molecule formed by the three molecules of oxygen with the chemical formula O$ _3$. It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope O$ _2$ and more reactive molecule.

When oxygen molecules absorb ultraviolet photons and undergo photolysis, ozone is obtained
$3O _2 \xrightarrow [photolysis]{UV : light} 2O _3$.

Ozone shields the surface of the earth from ultraviolet (UV) radiation from the sun. Ozone layer reduces the chances of skin cancer.

40 to 50% depletion in ozone layer occurs in the South polar region.
Ozone is destroyed by collisions with other atoms and molecules.
The large scale destruction of the stratospheric ozone first came into focus in 1987 through the experiments in antarctica.

Depletion of ozone layer is mainly due to Chloroflorocarbons.
Note:
The following describes the destruction of the ozone by chlorofluorocarbons.
Chlorofluorocarbons contains the chlorine molecule which reacts with ozone (O$ _3$) molecule and splits into O$ _2$ and O molecules.
Chlorofluorocarbons are used in refrigerators, air conditioners and aerosol sprays. They damage the ozone layer of the atmosphere.

Destruction of ozone can cause skin cancer, cataract and can hinder growth of plant. Ozone prevents the harmful radiations from reaching the surface of earth. The UV radiation has enough energy to cause adverse effects on all life systems, especially humans. It can destroy parts of DNA molecules that stores and propagate genetic information from one generation to another generation.

A chlorofluorocarbon (CFC) is composed of carbon, chlorine, and fluorine. This is used in refrigerants, propellants, and solvents. The chlorine atoms are released due to splitting of CFC by ultravoilet radiation.

The presence of CFCs in the atmosphere results in the depletion of the ozone layer. The chemical formula of this substance is CF$ _2$Cl$ _2$. They are used as coolants in refrigerators, coolers, etc. The CFCs causes the breaking of the ozone molecule which forms the oxygen radical and O$ _2$. The depletion of the ozone layer results in the penetration of the harmful UV radiations from the sun into the Earth's atmosphere. 

The correct answer is Stratosphere. Option C

Chlorofluorocarbons or Chlorofluoromethane are also known as freon or aerosols. They are chemicals used as refrigerants, propellants and solid plastic foams. These chemicals are also released as aerosols by jets flying at high altitudes. Along with nitrogen oxides, chlorofluorocarbons react with ozone of ozonosphere and depletes the same. Chlorofluorocarbons release reactive chloride which directly reacts with ozone molecules setting a chain reaction.

• Due to the ozone depletion, the UV rays are filtered in the Earth's atmosphere. 
• This ray results in the development of various diseases. One of the common disorder is erythema. 
• This is a disease in which there are reddening and swelling of the skin. There is swelling of the mucous membranes. 
• There is an increase in the blood flow from the peripheral capillaries which results in inflammation.
• Thus, the correct answer is option D. 

CFCs (Chlorofluorocarbons) are the most well-known pollutants responsible for the catalytic destruction of the ozone layer in the stratosphere.

Free radicals have unpaired electrons. These are extremely reactive. As one chlorine free radical can remove 11000 ozone molecules from stratosphere.

• Nitrous oxide is stable at ground level and breaks down when it reaches the stratosphere to form nitrogen oxides, that trigger ozone-destruction. 
  
• The main cause of ozone depletion are halocarbon refrigerants, such as chlorofluorocarbons (CFCs), HCFCs, halons).
  
• So, the correct option is 'Both B and C'.
  

Ozone layer is formed in the stratosphere of the atmosphere by the action of UV rays on the oxygen molecules. This ozone layer acts as absorbant for the harmful UV radiations and so, these radiation do not cross the troposphere to reach the earth's surface. However, the ozone depleting pollutants like chlorofluorocarbons reach the stratosphere and break when exposed to the UV rays. This process releases the reactive chlorine which further reacts with ozone to form simple oxygen. That is how the ozone layer is depleted. Hence, the correct answer is 'Chlorofluorocarbons'.

Ultraviolet radiations cause photochemical splitting of oxygen molecules in the stratosphere. The nascent oxygen combines with molecular oxygen to form ozone. In troposphere nascent oxygen comes from nitrogen dioxide.

ODS refers to the ozone-depleting substances like chlorofluorocarbons, methyl bromide, methyl chloroform, carbon tetrachloride, hexaflurocarbons that release the chlorine and oxides of chlorine. These react with the UV rays and ozone to release the nascent oxygen. 

The ozone depleting substances include the chlorofluorocarbons, oxides of nitrogen, methyl bromide, carbon tetrachloride etc because these split up when exposed to UV radiations and release the reactive chlorine and bromine. These reactive species of chlorine and bromine then react with ozone to release the nascent oxygen. Sulphur dioxide and carbon dioxide are greenhouse gases. Carbon monoxide is an air pollutant.

Ozone hole refers to the depletion of the ozone layer present in the stratosphere of the atmosphere. The chlorofluorocarbons are the paraffinated halogens that enter the stratosphere with winds and split up when exposed to the UV rays. They release reactive chlorine which further reacts with the ozone to release diatomic oxygen. The ozone hole shows a low concentration of ozone which is less than 220 DU. It is more prominent over Antarctica due to polar vortex and formation of the polar stratospheric clouds.

The ozone layer in the stratosphere is useful because it absorbs the UV radiations from the sun and prevents them from reaching the earth's surface. The depletion of the ozone by the ozone-depleting substances causes the break down of the ozone resulting in the ozone depletion. Due to this, the lives on the earth's surface are exposed to the UV rays. These UV rays induce mutations in the DNA by distorting its structure, leading to the erroneous function and replication of the DNA. The uncontrolled errors at times cause uncontrolled cell proliferation, causing skin cancer.

Among the five layers of the earth's atmosphere, ozone is present in the stratosphere which absorbs UV radiation before it reaches the ground. The main cause of ozone depletion is manufactured chemicals especially CFCs, these compounds reach the stratosphere by winds, where they release halogen atoms through photodissociation and cause the breakdown of ozone into oxygen. The ozone hole formed due to this increase the exposure of direct UV rays on earth carrying the potential risk of skin cancer and other negative effects

Ozone is found in high concentration in the stratosphere of the earth's surface in the form of ozone blanket or commonly known as the ozone layer. The vital function of ozone is to absorb the sun's ultraviolet radiation before it reaches the ground hence protecting the earth from its harmful effect. But the ozone-depleting substance such as Chlorofluorocarbons, nitrous oxides, etc that reacting with the ozone layer by releasing the reactive chlorine and cause depletion of it forming ozone hole. The concentration of ozone is less than 220 DU in the hole.

• The Vienna Convention for the Protection of the Ozone Layer is a multilateral environmental agreement signed in 1985.
• It provided frameworks for international reductions in the production of chlorofluorocarbons due to their contribution to the destruction of the ozone layer and the resulting increase in the threat of skin cancer.
• The Number of ozone depleters identified by Viena convention for Protection of Ozone Layer (1992) is 19.
• So, the correct answer is '19'.

Ozone is a triatomic gas that forms a shield or layer in the stratosphere region of atmosphere. This layer protects the living beings from harmful effects of UV-B rays of 280-320 nm. Depletion of the ozone layer can lead to an increased incidence of skin cancer.

CFCs (Chlorofluorocarbons) are the primary chemical compounds identified as the main cause of ozone layer depletion.

Ozone depletion allows more harmful UV radiation to reach Earth's surface, which damages skin cells and increases the risk of melanoma (skin cancer). Ozone accumulation would have the opposite effect, while acid rain and allergens are not directly linked to skin cancer.

High-flying aircraft, particularly supersonic jets, release nitrogen oxides and other pollutants directly into the stratosphere. These substances catalyze the breakdown of ozone molecules, leading to the depletion of the ozone layer.

Chlorine free radicals act as catalysts in the stratosphere, where they react with ozone (O3) to form oxygen (O2) and chlorine monoxide. This process destroys ozone molecules, which is the primary cause of ozone layer depletion.

Scientific evidence regarding the depletion of the ozone layer, particularly the role of CFCs, gained significant attention and was widely published in the 1980s following the discovery of the Antarctic ozone hole in 1985.

Carbon tetrachloride (CCl4) is a well-known ozone-depleting substance historically used as a solvent in industrial and laboratory applications. While CFCs are also ozone-depleting, the question specifically asks for a solvent.

The reaction between a chlorine free radical (Cl) and ozone (O3) produces chlorine monoxide (ClO) and molecular oxygen (O2).

Chlorofluorocarbons (CFCs) and carbon tetrachloride (CCl4) are both significant ozone-depleting substances. Carbon tetrafluoride (CF4) is also recognized as a greenhouse gas with potential atmospheric impacts, making all listed options contributors to the broader issue.

Nitric oxide and other nitrogen species react with ozone in the stratosphere, leading to the catalytic destruction of ozone (O3) molecules.

The Vienna Convention for the Protection of the Ozone Layer was the first global conference and treaty, held in 1985, to address the issue of ozone depletion.

In HCFCs, the chlorine atom is the primary agent that is released in the stratosphere and participates in the catalytic cycle that destroys ozone molecules.

Ozone depletion in the stratosphere has resulted in formation of a large area of thinned ozone layer, commonly called as the ozone hole. UV radiation of wavelengths shorter than UV-B, are almost completely absorbed by Earth's atmosphere, given that the ozone layer is intact. But, UV-B damages DNA and mutation may occur. It causes aging of skin, damage to skin cells and various types of skin cancers. In human eye, cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of cornea, called as snow-blindness, cataract, etc. Such exposure may permanently damage the cornea. Thus, the correct answer is option D.

Ozone layer is a region of concentration of ozone molecule. $O _3 (O _2+ O)$ in the earth's atmosphere. The layer lies in the stratosphere at an altitude of 18-50 kms. The ozone layer naturally Shields earth's life from the harmful effect of the Sun's ultraviolet radiations.

Ozone is an inorganic molecule. It is a pale blue gas with a distinctively pungent smell. In the environment ozone is known for its both harmful and useful effects.
Ozone present in stratosphere is useful as it act like shield and protect the earth from harmful UV-rays which can cause serious problems like skin cancer and decrease in level of photosynthesis. Ozone present in troposphere act as pollutant and have many deleterious effects. 

Therefore, the correct answer is option C.

Ozone depletion causes the harmful UV-B radiations to strike the earth surface. These radiations are capable of causing various health issues like malignant skin cancers, cataract, decreased immunity, decreased primary productivity, chlorophyll bleaching etc. 

The UV-C radiations breakdown the bonds in the chlorofluorocarbons (CFCs) to release the chlorine monoxide and the nascent chlorine. These further react with the ozone to split it into ordinary oxygen molecules. The oxygen molecules are further broken down into nascent oxygen, which acts as the radicle. 

Polar spring, also known as the Antarctic Spring is the period from late August to early October and the strong westerlies circulate around the Antarctic continent creating a polar vortex. The polar vortex results in the formation of the polar stratospheric clouds which trap most of the gases including the ozone-depleting factors like CFCs, methyl bromide etc. 

In the stratosphere of the atmosphere, the UV rays are concentrated and these react with the oxygen to produce the ozone. This ozone persists in the form of the ozone layer and acts as the absorbent for the UV rays. Ozone layer does not allow the UV-B and UV-C from hitting the earth's surface, thereby preventing the various harmful after effects. Sulphur dioxide, carbon monoxide and methane are the primary pollutants of air.

The ever increase in the use of ozone-depleting substances like CFCs, HFCs, methyl bromide etc. will continue destroying the ozone layer in the stratosphere. The depletion of the ozone layer will result in the penetration of more UV-A and UV-B radiations to the earth surface. These radiations are strong mutagens as they distort the structure of the skin cell DNA when the skin is exposed to the UV rays. It results in skin related disorders like pigmentation, skin cancer etc. 

Chlorofluorocarbons are the halogenated paraffin hydrocarbons containing chlorine, fluorine and carbon. These have been extensively used as the refrigerants and the spray propellants due to their non-toxic nature. But, the CFCs have found their way to the stratosphere of the atmosphere where the incidence of the UV rays is very high. The CFC splits up when exposed to the UV rays and release the reactive chlorine species. This is harmful to the ozone in the stratosphere because the chlorine reacts with ozone to release the simple oxygen, that is further converted to the reactive nascent oxygen.

The main cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbon refrigerants, solvents, propellants and foam-blowing agents (chlorofluorocarbons (CFCs), HCFCs, halons), referred to as ozone-depleting substances (ODS). These compounds are transported into the stratosphere by the winds after being emitted from the surface.[2] Once in the stratosphere, they release halogen atoms through photodissociation, which catalyze the breakdown of ozone (O3) into oxygen (O2).[3] Both types of ozone depletion were observed to increase as emissions of halocarbons increased.

Oxides of nitrogen find their way to the environment when they are released from the fertilizers, farms, combustion of coal etc. These bear a similarity to the paraffinated halogens like the chlorofluorocarbons when they reach the stratosphere of the atmosphere. They get unstable when exposed to the UV rays and the reactive nitrogen atom recs with the ozone to form the nitrogen dioxide and the diatomic oxygen molecule, similar to the reaction catalysed by the CFCs which release reactive chlorine that break down the ozone.

Ozone is found in high concentration in the stratosphere of the earth's surface in the form of ozone blanket or commonly known as the ozone layer. The vital function of ozone is to absorb the sun's ultraviolet radiation before it reaches the ground hence protecting the earth from its harmful effect. But the ozone-depleting substance such as Chlorofluorocarbons, nitrous oxides, etc that reacting with the ozone layer cause depletion of it forming ozone hole.

Among the five layers of the earth's surface ozone is present in the stratosphere which absorbs UV radiation before it reaches the ground. The main cause of ozone depletion is manufactured chemicals especially CFCs, these compounds reach the stratosphere by winds, where they release halogen atoms through photodissociation and cause the breakdown of ozone into oxygen. The ozone hole formed due to this increase the exposure of direct UV rays on earth carrying the potential risk of skin cancer and other negative effects. Direct exposure of harmful UV rays that penetrates skin can damage the genetic material I.e., DNA in skin cells and if the body is unable to recover the damage the cells stars to divide and grow uncontrollably which eventually leads to a tumour.

Among the five layers of the earth's surface ozone is present in the stratosphere which absorbs UV radiation before it reaches the ground. The main cause of ozone depletion is manufactured paraffinated halogen chemicals especially CFCs, these compounds reach the stratosphere by winds, where they release halogen atoms through photodissociation and cause the breakdown of ozone into oxygen. The ozone hole formed due to this increase the exposure of direct UV rays on earth carrying the potential risk of skin cancer and other negative effects.

The intermediary lobe of the pituitary gland secreted the Melanocyte Stimulating Hormone (MSH) that acts on the types of cells in the skin called the melanocytes. These cells produce a coloured pigment called the melanin which diverts the UV-A radiations falling on the skin. This prevents the UV rays from reaching to the other sensitive cells of the body and prevents the possible damages to the DNA that can be caused by them. This is the reason that body develops tanning when exposed to the bright sunlight. It is a protective mechanism.

The ozone layer is part of the earth's atmosphere. Ozone is basically found in the stratosphere. Ozone layer contains the high concentration of ozone. It's is vital to human life on earth because it absorbs biologically harmful ultraviolet radiations from the sun. Direct exposure to such rays can cause serious illness and skin problems. The main cause of ozone depletion is manufactured chemicals especially CFCs, these compounds reach the stratosphere by winds, where they release halogen atoms through photodissociation and cause the breakdown of ozone into oxygen. The ozone hole formed due to this increase the exposure of direct UV rays on earth carrying the potential risk of skin cancer and other negative effects.

Methyl bromide, halon, nitrogen oxides and chlorofluorocarbons are the potent ozone-depleting substances. These accumulate in the stratosphere and undergo photodissociation when exposed to the UV rays. The reactive chlorine and bromine react with ozone to form diatomic oxygen and molecular oxygen.

The exposure to the UV radiations have an ionizing and distorting effect to the body of the humans. It causes damage to the eyes by destroying the essentials of the eye-lens. The sunburn occurs due to high intensity. Skin cancer is caused due to distortion of the DNA by the formation of the pyrimidine dimers, such that the DNA cannot be replicated properly.

•  The UV region covers the wavelength range 100-400 nm and is divided into three bands: UVA (315-400 nm) UVB (280-315 nm)
• The most common form of UV radiation is sunlight, which produces three main types of UV rays: UVA, UVB, UVC.
• At certain wavelengths, UV is mutagenic to bacteria, viruses and other microorganisms. Particularly at wavelengths around 260–270 nm, UV breaks molecular bonds within microorganismal DNA, producing thymine dimers that can kill or disable the organisms.
• UVB, the chief cause of skin reddening and sunburn, tends to damage the skin's more superficial epidermal layers. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging.

Cataracts and blindness are among the most common eye diseases associated with further ozone layer depletion and increased UV-B at the Earth's surface.  A 1% decrease in stratospheric ozone may result in 100,000 to 150,000 additional cases of blindness due to eye cataracts worldwide. The ozone layer is responsible for absorbing harmful ultraviolet rays, and preventing them from entering the Earth's atmosphere.

• CFCs and other halogenated ozone depleting substances (ODS) are mainly responsible for manmade chemical ozone depletion.
• The total amount of effective halogen (Chlorine and bromine) in the stratosphere can be calculated and are known as the equivalent effective stratospheric chlorine.

The ozone layer (ozonosphere) is generally found in the stratosphere. Its altitude varies, being lower at the poles (around 11-16 km) and higher at the equator.