[Biology Class Notes] on Ozone Layer and It's Depletion Pdf for Exam

Ozone layer, also named as ozonosphere, is present in the stratosphere region, which is the upper-atmosphere region, between about 15 – 35 km (9-22 miles) above Earth’s surface, containing relatively high ozone molecules (O₃) concentrations. 

The ozone layer effectively blocks almost all solar wavelength radiation of less than 290 nanometers from reaching the surface of the Earth, including some types of ultraviolet (UV) and other sources of radiation that could harm or destroy most living organisms.

What is Ozone Layer Depletion?

Ozone gas in the stratosphere is continuously formed by the action of UV rays on molecular oxygen, and also degraded to molecular oxygen. The stratosphere will strike a balance between development and ozone depletion. By late, chlorofluorocarbons (CFCs) have disturbed the equilibrium due to increased ozone depletion.

The CFCs find widespread use as coolants. In the lower part of the atmosphere, discharged CFCs move upwards and reach the stratosphere. UV rays act on them in the stratosphere, releasing atoms of Cl. Cl degrades ozone that releases molecular oxygen, with these atoms merely serving as catalysts; Cl atoms are not consumed in the answer. Consequently, whatever CFCs are applied to the stratosphere, they are indefinitely and continuously show effect on Ozone levels.

While ozone depletion occurs widely in the stratosphere, the depletion is especially marked over the Antarctic region. This contributed to the creation of a wide area of thin ozone layer, widely known as the ozone hole.

Ozone in the stratosphere is a result of the dioxygen (O₂) molecules that act on UV radiations. The UV radiation separates molecular oxygen into free (O) atoms. Such atoms of oxygen interact with the molecular oxygen to form ozone

[O_{2}(g) overset{uv} rightarrow O(g) + O(g) ]

[ O(g) + O_{2} (g) overset {uv} rightleftarrows O_{3}(g) ]

Ozone Layer Depletion Reaction

CFCs interact with the usual atmospheric gases once they are released into the atmosphere and ultimately enter the stratosphere. In the stratosphere, powerful UV radiations break them down, releasing chlorine-free radicals

[CF_{2}Cl_{2}(g) rightarrow Cl(g) + C˙ F_{2} Cl (g) ] (in the presence of sunlight )

Chlorine monoxide radical reacts with atomic oxygen yields more chlorine radicals.

[ClO O˙(g) + O(g) →→C˙C˙l(g) + O₂(g) ]

The chlorine radicals are regenerated continuously and cause an ozone breakdown. CFCs thus transport agents to the stratosphere for the continuous generation of chlorine radicals and to damage the ozone layer.

Chemicals, in particular manufactured halocarbon refrigerants, solvents, propellants, and foam-blowing agents (chlorofluorocarbons (CFCs), HCFCs, halons), called ozone-depleting substances (ODS), are the main cause of ozone depletion and the ozone hole.

After being expelled from the surface these substances are transported into the stratosphere through turbulent swirling, much faster than the molecules can settle.

When halogen atoms are released in the stratosphere by means of photodissociation, which catalyzes the breakdown of ozone (O₃) into oxygen (O₂). All forms of loss of ozone were found to increase as the halocarbon emissions increased.

Causes of Ozone Layer Depletion

Causes can be categorized into two types. They are

Natural Causes of Depletion of Ozone Layer

Some natural phenomena such as Sun-spots and stratospheric winds have been found to affect the ozone layer. But this has been found to cause the ozone layer to deplete no more than 1-2 percent and the results are also assumed to be only temporary. 

 

Man-Made Causes of Depletion of Ozone Layer

The main reason of ozone depletion is determined as excessive chlorine and bromine release from man-made compounds, such as chlorofluorocarbons (CFCs)

Effects of Ozone Layer Depletion

When the ozone layer is depleted, this means that humans are overly exposed to strong UV light. Overexposure to heavy UV light causes skin cancer, cataracts, sunburns, immune system weakening and accelerated aging.

Many species of crops are susceptible to strong UV light, and overexposure can result in minimal growth, photosynthesis and flowering. Some of the UV-vulnerable crop species include barley, wheat, corn, oats, rice, broccoli, tomatoes, cauliflower, to name only a few. Forests bear the brunt of ozone depletion in the same way.

Certain marine life is greatly impacted by exposure to strong ultraviolet rays, particularly planktons. Planktons appear high up in the aquatic food chain. If planktons decrease in number due to destruction of the ozone layer, it would disrupt the marine food chain in many ways.

Too much Ultraviolet radiation could also cause skin and eye cancer in domesticated animals.

Too much ultraviolet radiation massively degrades materials such as plastics, wood, fabrics, rubber

Prevention of Ozone Layer Depletion

Pesticides are perfect chemicals to rid the farm of pests and weeds, but they do make an immense contribution to deplete the ozone layer. Applying natural methods is the surefire solution to get rid of pests and weeds. Just manually weed your farm, and use alternative, environmentally friendly chemicals to alleviate pests.

Limiting the number of vehicles on the road is the simplest strategy to reduce ozone depletion. Such vehicles emit a lot of greenhouse gases, which ultimately form smog, a catalyst in ozone layer depletion. Most cleaning supplies products are loaded with harsh chemicals that find their way into the atmosphere, ultimately contributing to ozone layer degradation. To arrest this case, using the safe and environmentally friendly cleaning materials.

The Montreal Protocol that was developed in 1989 significantly helped to restrict chlorofluorocarbons (CFCs). Nitrous oxide, which is a proven hazardous chemical that can kill the ozone layer, has never been included in the protocol however. Nowadays nitrous oxide is still in use. Governments must act now and ban the use of nitrous oxides to reduce the rate of ozone depletion

Key Points

Ozone in the stratosphere, which shields us against the harmful effects of ultraviolet radiation, is rapidly depleting due to CFC pollution, thus raising the risk of skin cancer, mutation and other disorders

Depletion of ozone and the ozone hole has created concern worldwide about rising cancer risks and other negative impacts. The ozone layer prevents most damaging Solar rays from passing into the Earth’s atmosphere through ultraviolet radiation (UV light).

These wavelengths cause skin cancer, sunburn, permanent blindness and cataracts that have been predicted to rise significantly as a result of thinning ozone, as well as harming plants and livestock. Such concerns led to the Montreal adoption

1987 Protocol restricts the production of CFCs, halons and other ozone de
pleting chemicals.