[Chemistry Class Notes] on Effects of Ozone Layer Depletion Pdf for Exam

The ozone layer is a region in Earth’s stratosphere where a higher concentration of Ozone gas is present. It is considered “good” in the stratosphere as it absorbs some of the sun’s harmful UltraViolet radiations and hence protects lives on Earth.However, in recent studies, scientists have observed changes in equilibrium between the formation and destruction of Ozone due to the influx of various substances into the atmosphere which reacts with ozone and destroys it.

Ozone layer is present in the upper part of the atmosphere. It is often found in the upper part of the stratosphere. It protects the earth from the harmful ultraviolet rays of the sun. harmful UV rays of the sun are very harmful for human beings as the rays can cause skin cancer. The ultraviolet rays break the oxygen molecule into free oxygen atms and the free oxygen atoms combine with the oxygen molecule to form ozone. This layer lies at a close distance beyond the earth surface.

Ozone -Defensive Shield of the Earth

The ozone layer is a shield that is found in the stratosphere of the earth’s atmosphere. It helps in protecting the earth from the harmful ultraviolet radiations of the sun.

The ozone layer, a fragile shield of gas, preserves the Earth from the harmful portion of the rays of the sun, thus helping protect life on the planet.

Preparation of Ozone

 It is an allotropic form of oxygen and it is formed by passing dry oxygen through a silent electric current. During this process a part of the oxygen molecule dissociates to form atomic oxygen which combines with a molecule of oxygen to give allotropic form of oxygen. This product is called ozonized oxygen.

Ozone Structure

Ozone is a polar molecule and we will look at the structure of ozone. Ozone resonates between two structures such as given here:

What Does Ozone Layer Depletion Mean?

Ozone Layer depletion is the significant decrease in the concentration of ozone in the upper layer of the atmosphere caused due to the reaction of chemical compounds containing chlorine and bromine. It implies that the rate at which the Ozone is being destroyed is much faster than the rate at which it is being formed.

Causes of Ozone Layer Depletion?

1. Chlorofluorocarbons: These are made up of Chlorine, Fluorine and Carbon. They are released into the atmosphere by discarded refrigerators, aerosols, solvents, etc. Molecules of CFCs when exposed to UV radiation break up, thus freeing Chlorine atoms. This free chlorine atom reacts with Ozone and depletes it.

2. Nitrogenous Compounds: like NO₂, NO, N₂O are responsible for ozone depletion. The sources of Nitrogen Oxides are mainly explosions of thermonuclear weapons, agricultural fertilizers and industrial emissions. 

3. Bromine Compounds: These are called Hydrobromofluorocarbons (HBFCs) and are used in fire extinguishers. Each bromine atom destroys a hundred times more ozone molecules than a chlorine atom does.

4. Natural Causes: The ozone layer is depleted by a number of natural causes like the sunspot cycle, volcanic eruption. However, the percentage effect is less i.e around 1-3%. 

5. Fossil fuels destroy the ozone layer. The three main forms of fossil fuels are oil, natural gas, and coal. Fossil fuels are used in cars, factories, and for electricity. These fuels are called fossil fuels as fossil fuels have been formed from the organic remains of prehistoric plants and the animals.

Properties of Ozone

• Ozone is blue in its pure form and has a strong disturbing smell but in a limited proportion it has a pleasant smell.

• It can absorb the harmful UV rays of the sun.

• The boiling point of ozone is 161.2K and gives violet blue crystals when solidified. Its melting point is 80.6K

• It is a strong oxidizing agent because it is an unstable compound which decomposes very quickly.

 

What are Ozone Depleting Substances?

Ozone Depleting Substances are those which deplete the Ozone layer by reacting with Ozone and thus thinning the Ozone layer. The number of substances and their sources is present in the following table:

What are the Environmental Effects of Ozone Depletion?

Reduction in the quantity of Ozone implies increased penetration of solar UV-B radiations to the Earth’s surface. It has devastating effects on human health, animals, plants, microorganisms and air quality.

Effects on Human Health and Animal Health

1. People become vulnerable due to the increase in the incidence of morbidity from eye diseases, skin cancer and infectious diseases.

2. In light skin coloured populations, UV_B radiation is the main risk factor for the development of Non-Melanoma skin cancer.

Effects on Plants

1. Psychological processes of plants are affected by UV-B radiation.

2. Response to UV-B also varies voraciously among different species. Therefore, in agriculture, it becomes necessary to use more UV-B tolerant species.

3. In forests and grasslands, it results in changing the composition of species.

4. There are several indirect changes like plant form, biomass allocation of the plant, timing of development phases triggered due to UV-B radiation.

Effects on Aquatic Ecosystems

1. More exposure to UV-B radiation has affected motility in phytoplanktons which results in reduced survival rates of these organisms.

2. UV-B radiation has been found to cause damage in the early development stages of fish, crabs, amphibians and various other animals. The more severe effect is a decrease in reproductive capacity.

Effects on Air Quality

1. Reduction of Ozone in upper layers of atmosphere and the direct increase of UV-B radiation penetrating to the lower atmosphere results in higher photodissociation rates of gasses that control the chemical reactivity of the Troposphere.

2. Products formed due to these reactions are know
n to have adverse effects on human health, plants and outdoor materials.

3. Increase in tropospheric reactivity will lead to increased production of particulates due to oxidation and nucleation of sulfur due to anthropogenic and natural causes.

Effects on Materials

1. Materials like polymers, naturally occurring biopolymers and some other materials of commercial interest are affected by UV radiations.

2. Increase in solar UV-B content due to partial ozone depletion accelerates the photodegradation rate of these materials and therefore limits their life outdoors.

The Solution to Address the Problem of Ozone Layer Depletion

Instead of using chemicals, one should stop using pesticides and switch to natural methods to get rid of pests. A significant amount of greenhouse gasses are produced by cars, contributing to global warming as well as ozone depletion. The use of vehicles should therefore be reduced as much as possible. Many of the materials used for cleaning have chemicals that damage the ozone layer. We should substitute eco-friendly goods for that. Maintain air conditioners, as CFC escapes into the atmosphere via their malfunctions. 

How Can We Protect the Ozone Layer?

• Avoid the consumption of gasses that are harmful for the ozone layer due to their content and manufacturing process.

• Reduce use of vehicles

• Avoid using cleaning products that cause harmful effects to the environment and human beings.

• Use natural and local products

• Avoid excessive use of appliances having chlorofluorocarbons like refrigerators and AC.