Ozone layer and its depletion, Biology

Assignment Help:

About 90% of ozone of atmosphere resides in stratosphere (16 to 40 km) layer of atmosphere as ozone layer. It protects life on this planet from harmful U.V. radiations. In absence of this layer the U.V. radiations would have caused disastrous effect on life.

Ozone is formed by multi-step photochemical reaction:

                     O2 + UV (242 nm) 399_hydrocarbon.png O+O

                               O2 (g) + O 399_hydrocarbon.png   O3

Thickness of ozone layer is measured in Dobson units (DU). It was observed iin mid 1970s that some human activities are destroying thickness of ozone layer. Ozone depletion is caused by following types of compounds.

(i)     Chlorofluoro  (Freon's) (CCI2F2)

(ii)   Nitric oxide (NO)

(iii) Reactive hydroxyl radicals (OH)

Mechanism of ozone depletion:

(i)     Chlorofluorocarbons:

CFC's are stable at earth surface but at high altitude of 15-30 km they decompose to form chlorine atoms in presence of U.V. radiations.

                     CCL2 F2 + hv  399_hydrocarbon.png  CI0 + CCIF2

                        CL0 + O3    399_hydrocarbon.png    CIO0 + O2

                              O3  + hv  399_hydrocarbon.png  O2 + O0

The Oxygen Atom Reacts With CIO to produce more CI0 leading to further loss of O3.

                     O + CIO0   399_hydrocarbon.png CI0 + O2

                     CI0 + O3   399_hydrocarbon.png  CIO0 +O2

            O +O3    399_hydrocarbon.png  2O2           

CFC's are mainly used propellants in aerosol sprays, as coolant in refrigerating equipments.

(ii)   Nitric oxide molecule:

The emissions of nitrogen oxide by high flying supersonic aircrafts and nuclear explosion have been found to be responsible for ozone depletion.

                                 NO + CIO0  399_hydrocarbon.png   CI0 + NO2

                                   CI0 + O3 399_hydrocarbon.png  CIO0 + O2

                                   NO + O3  399_hydrocarbon.png  NO2 + O2

The CI0 is formed in chain reaction leading to ozone depletion actually 105 molecules of ozone are converted into oxygen by a single chlorine atom.

(iii) Hydroxyl radicals:

Hydroxyl ions produced by photo dissociation of water molecules in the atmosphere, which reacts with ozone molecules to produce HO2, which reacts  with another O3 molecules to field hydroxyl ions again.

                                 OH + O3  399_hydrocarbon.png   HO2 + O2

                                 HO2 + O3  399_hydrocarbon.png OH + 2O2

OH  ion is again regenerated which leads to chain reaction.

Main causes of ozone depletion:

(i)     Excessive use of chlorofluorocarbons (CFC's)

(ii)   Excessive use of nitrogenous fertilizers.

(iii) Combustion of fossil fuels and organic matter.

(iv) Nuclear explosions.

(v)   Supersonic aircrafts, rockets and space shuttles.

Effect of ozone depletion:

1.      Exposures to U.V. radiations damages the cornea and lens and lens of eye causing blindness.

2.      The excess U.V. radiation cause sun burn, skin cancer and various kinds of damages to animals and plants.

3.      The genetic material DNA has capacity to absorb U.V. radiations which may cause DNA breakage inhibition and alteration of DNA's replication.

4.      U.V. radiations causes leukemia and breast cancer.

5.      It may cause lung cancer, lungs injury, dizziness, visual impairment.

6.      Ozone depletion has strong effect on climate change  indirectly.

7.      Many micro-phytoplankton would die because of their exposure to U.V. radiation.

 

Measures for protecting ozone depletion:

In 1987 a global agreement was assigned by 30 countries in montreal for the reduction in production and consumption of ozone depleting substances.

Main objective:

(i)     Phase out production and consumption of CFC's by 2010.

(ii)   Phase out production and consumption of halogen as soon as possible.

(iii) Commitment to develop eco-friendly chemicals.

(iv) Scientific information, training and techniques must be given to developing of countries by developed countries.

Substitute for chlorofluoro carbons:

(i)     As CFC's are hazardous ozone depleting substances so there was a need to find a safe alternative for CFC's.

(ii)   Hydro- chloro- fluoro carbon (HCF'S) and HFC'S (hydro fluoro carbon) have proved to be a good substitute for CFC'S because of their low ODP (potential to release CI atmos and Their  Life time in the atmosphere).


Related Discussions:- Ozone layer and its depletion

Controlling introduction of alien species, Controlling Introduction of Alie...

Controlling Introduction of Alien Species As you know the alien species can cause the existing population to decrease or even become extinct. The individuals of alien species

Procedure for nelson somogyi method for glucose estimation, Explain Procedu...

Explain Procedure for nelson somogyi method for glucose estimation? Carry out the procedure following the steps enumerated herewith: 1. Label a series of  Folins tubes as bl

What is surgical therapy, Surgical Therapy The clinician may use a surg...

Surgical Therapy The clinician may use a surgical approach when non-surgical therapies are not indicated or are unsuccessful. The surgical techniques are modified from those

What do you mean by the coelom, Q. What is the coelom? To which structures ...

Q. What is the coelom? To which structures do coeloms give birth? Are all animals coelomate? Coeloms are cavities delimited by mesoderm and Coeloms originate the cavities where

Soils of tropical and temperate forests, Soils of Tropical and Temperate Fo...

Soils of Tropical and Temperate Forests Although soils of tropical forests are generally poor in nutrients they are able to maintain high productivity under natural conditions

Symptoms of dyspepsia, Q. Symptoms of dyspepsia? The life style modific...

Q. Symptoms of dyspepsia? The life style modification in terms of work schedules, eating behaviour like consuming meals when extremely tired, quitting alcohol and smoking would

Use of alternate metabolic pathways, Use of Alternate Metabolic Pathways ...

Use of Alternate Metabolic Pathways Plants surviving under water-logged conditions offer the simplest example of such a response. The submerged parts of such plants use the an

Tolerance range, Maximum and minimum range of an animal with the factors of...

Maximum and minimum range of an animal with the factors of Ph Salinity Pressure Relative human

What are compound eyes, Q. What are compound eyes? Arthropods have comp...

Q. What are compound eyes? Arthropods have compound eyes made of several visual units called as ommatidia. Each ommatidium transmits visual information through the optic nerve

How is plant tissues classified according to their functions, How is plant ...

How is plant tissues classified according to their functions? Plant tissues are separated into growth (embryonic) supporting, tissues, filling and photosynthetic tissues (groun

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd