Stratospheric Pollution

The upper stratosphere consists of considerable amount of ozone (O₃), which protects us from the harmful ultraviolet (UV) radiations (λ 255 nm) coming from the sun. These radiations cause skin cancer (melanoma) in humans. Therefore, it is important to maintain the ozone shield.

Ozone in the stratosphere is a product of UV radiations acting on dioxygen (O₂) molecules. The UV radiations split apart molecular oxygen into free oxygen (O) atoms. These oxygen atoms combine with the molecular oxygen to form ozone.

Ozone Layer

Ø The ozone layer is basically naturally occurring gas in the region of stratosphere where ozone particles are accumulated.

Ø Ozone layer is also naturally broken down but there is a balance between its formation and natural depletion.

Ø As a result the total amount of ozone remains constant. But ozone layer thickness varies with altitude and seasonal change. Ozone concentration is highest between 19 - 23 km.

Ø Most of ozone is formed at equator where there is maximum sunshine but with winds it travels at high altitude and get accumulated in stratosphere.

Causes of Ozone Layer Depletion

1. Chlorofluoro Carbon:

ü Ozone depletion occurs when the natural balance between the production and destruction of stratospheric ozone is disturbed.

ü Although natural phenomenon can cause ozone depletion but human activities such as CFCs are now accepted as major cause of depletion. All ozone depleting chemicals contain chlorine and bromine.

ü CFCs are highly volatile and non-combustible so they are very quickly evaporated and can easily reach in stratosphere where ozone is present here they start depleting ozone molecules.

ü These CFCs have also adverse affects on human health. According to the chemical model for ozone destruction proposed about 20 years ago, the photolysis of Cl₂O₂ is key to ozone depletion reaction.

ü But now atmospheric researchers studied that the rate of this reaction is not extremely high as it was thought previously so we can no longer say that CFCs are the main cause of ozone depletion.

2. Global Warming:

ü Global warming also leads to ozone layer depletion. Due to global warming and greenhouse effect most of the heat is trapped in troposphere which is the layer below the stratosphere.

ü As we all know ozone is present in stratosphere so heat don’t reaches troposphere and it remain cold as recovery of ozone layer requires maximum sunlight and heat so it leads to depletion of ozone layer.

3. Effects on Eyes:

ü The major cause of blindness in this world is cataracts. There would be 0.3% - 0.6% increase in risk of cataract if there will be 1% decrease in Ozone level. Eye lens can be damaged by oxidative agents.

ü Oxidative oxygen produced by UV radiation can severely damage eye lens and cornea of eye is also badly damaged by UV radiation. Photokeratitis, cataract, blindness all are caused due to UV rays.

4. Effects on Skin:

ü Exposure to UV radiations can cause skin cancer. UV radiations alter the structure of biomolecules and thus lead to different diseases.

ü Skin is the most often exposed part of body to UV radiations

ü There are two types of skin cancer,

o Melanoma

o Non-melanoma

ü Melanoma is most serious form of cancer and is often fatal, while non-melanoma is most common type and less fatal.

ü Depletion of ozone layer leads to both Sun burn and skin cancer. UV radiations are also responsible for breast cancer and leukemia.

5. Effects on Human Immunity:

ü Exposure to UV radiations can also result in suppression of immune response to skin cancer, infectious diseases and other antigens.

ü The immune supression is due to changes in skin photoreceptors and antigen presenting cells that are brought by UV radiations.

ü More increase in depletion of ozone results in more decrease in immune system.

6. DNA Damage and Lung Disease:

ü Short exposure to UV-B radiations can cause the DNA damage because UV radiations can disturb biomolecules such as lipids, proteins and Nucliec acids.

ü Due to UV-B radiations there would be cryptic transposable elements which may lead towards the mutations which is more dangerous than the immediate DNA damage.

ü Excessive UV-B radiation exposure results in the basal and squamous cells carcinomas. These types of cancers are induced due to transcriptional errors during DNA replication which are caused by changes in pyrimidine bases.

ü The ultimate cause of this whole mechanism is found to be the prolonged exposure to UV radiations. It is estimated that there is increase of 2% of incidence of these cancers by 1% depletion of ozone layer.

ü Exposure to UV radiations equally affects lungs. Bronchitis, obstruction of lungs Emphysema, asthma all can be resulted from UV radiations exposure.

7. Effects of Food Storage and Human Population:

ü Depletion of ozone layer is also causing the problem of food shortage to humans. UV radiations are disturbing developmental and physiological processes which is decreasing the productivity of crops.

ü As humans are heavily dependent on crops for food so there is a great chance if depletion of ozone layer is not checked it may cause seriously shortage of food to humans.

ü Researches also show that UV radiations can also be used to enhance yield of crops by the use and application of phytohormones.