World Ozone Day - September 16 | Causes and Effects of Ozone Depletion - Ozone Hole | Environmental Chemistry Notes

• September 16: International  Ozone Day | Ozone Day Theme 2023
• Ozone is present mainly in the stratosphere extending 16 kms -50 kms.
• Also known as ozone umbrella, or protective layer.
• The presence of ozone layer in the stratosphere is of vital importance for all living organisms, because the harmful solar radiation, such as ultraviolet rays(UV-B), which are lethal to life on the earth are absorbed by it.
• The ozone umbrella does not allow these harmful UV rays to enter the earth’s atmosphere.

Ozone hole

• The thickness of ozone layer is measured in Dobson unit (DU),where 

                                 1 DU =0.01mm

• The average thickness of the stratosphere ozone layer is estimated to be 32 Du
• A fall in thickness or concentration of spring time ozone layer is termed as ozone hole.
• It was discovered by Farman et al 1985, who coined  the term ozone hole.

Causes of Ozone depletion

• The main cause of ozone layer depletion is the build-up of CFCs (chlorofluorocarbons) in the atmosphere.

• When the CFCs reach the upper atmosphere, high UV radiation reacts with CFCs and releases chlorine atoms. These free chlorine atoms react with ozone thereby leading to the depletion of the ozone layer.

CFCl₃-> CFCl₂+Cl

CFCI₂ ->CFCI+CI

CI+O₃->CIO+O₂

CIO+O₃->CI+2O₂

•  An individual chlorine atom can on average destroy nearly a thousand ozone molecules before it is converted into a form harmless to ozone this is why CFCs are extremely damaging to the ozone layer.
•  The build-up of CFCs is caused by many applications like the production of refrigerants, anesthetics, aerosol sprays.

Social issues and the environment :Climate change, Global warming and Acid rain, Green house effect, ozone layer depletion from Biology Exams 4 U

Ozone Depleting Substances (ODS)

• The green house gases like CFC, Methane and nitrous oxide in the stratosphere destruct ozone layer.
• Substances that cause the depletion of the ozone layer are called Ozone Depleting Substances (ODS).

The different ODS are

• CFCs (14% of total depletion)
• Nitrogen oxides(3.5% depletion)
• Halons (Used in fire extinguishers)
• Methyl Chloroform
• Carbon Tetrachloride
• Hydrofluorocarbons (HCFCs)

Effects of Ozone Depletion

• Due to depletion of ozone layer the dangerous UV B radiation passes through this layer and reaches the earth.
• Cornea absorbs UV b radiations and becomes inflamed. The disorder is called ‘snow blindness’ cataract
• The incidence of UV B radiation damage skin cells cause ageing of skin and skin cancer.
• Decreased photosynthetic activity will increase CO2 concentration of the atmosphere resulting in global warming.