Causes and Effects of Ozone Depletion

Discuss the various causes and effects of ozone depletion.

The steady and gradual thinning of the protective layer of Earth, the ozone layer, is called ozone layer depletion. This depletion leaves a hole in the ozone layer, which exposes the Earth to harmful rays from the sun. 

The synthesis of ozone occurs in the stratosphere from molecular oxygen when it absorbs UV radiation. However, ozone is continuously removed due to various chemical reactions that convert it back to molecular oxygen. 

The concentration of ozone depends on the balance of these reactions. The reduction in this ozone concentration is commonly known as ozone depletion. 

Causes of Ozone Depletion

When exposed to UV light, some chemical compounds containing chlorine and bromine release these elements into the stratosphere. They interact with ozone to break it into molecular oxygen. 

One chlorine atom can destroy almost 100,000 ozone molecules, and one bromine atom is 40 times more powerful than chlorine. 

The chemical compounds that have these elements that destroy ozone are chlorofluorocarbon (CFC), hydrobromofluorocarbon, halons, etc. Such compounds that deplete ozone are called ozone-depleting compounds.

These are manmade compounds emitted as a result of the usage of common products such as refrigerators, air conditioners, aerosols, etc. Apart from these chemicals, water vapour and nitrous oxide also take part in ozone depletion. 

Major Ozone-Depleting Substances

The ozone-depleting substances all interact with ozone in one way or the other and degrade it with atoms and molecules released by them. 

• CFC: Chlorofluorocarbons that have 1-3 carbon atoms and at least one chlorine and fluorine atom. They are emitted from aerosols, refrigerators, sprays, solvents, etc. These CFC molecules reach the atmosphere, where it is exposed to the UV Rays. This interaction acts on the molecule will eventually release chlorine. Chlorine, in turn, reacts with the ozone molecule and degrades it.
• Unregulated Rocket Launches: The process of rocket launching is another major cause of ozone depletion.
• Hydrochloroflurocarbons (HCFCs): These compounds will have an additional hydrogen atom than the CFCs.
• Hydrobromoflurocarbons _HBFCs): These are compounds with 1-4 carbon atoms, and at least one bromine, one fluorine atom, and one hydrogen atom.
• Methyl Bromide
• Methyl Chloride from the ocean
• Carbon tetrachloride, which has a lifetime of almost 26 years, can cause considerable damage to the ozone layer.
• Methyl Chloroform emitted by terrestrial and oceanic ecosystems is are source of chlorine that can damage ozone, even though they have a very short lifetime.
• Nitrogenous Compounds such as NO, N^₂O, and NO₂, emitted in small amounts due to various human activities, are also considered to be responsible for ozone depletion.
• Halons
• Bromochloroform is another short-lived gas containing bromine that can damage ozone.

Effects of Ozone Depletion

The ozone layer protects the Earth from harmful UVB radiation and thus helps regulate the climate. In the absence of the ozone layer or having a hole in this layer, UV radiation gets access to the Earth’s surface. Exposure to this radiation causes harmful effects on plants, animals, and humans. It causes, 

• Reduced crop growth and yield by affecting the rate of photosynthesis, flowering, and growth.
• Affects the overall productivity of natural ecosystems and biodiversity.
• Causes skin cancer in humans with longer exposure to UV radiation.
• Elderly and children with respiratory disorders may be vulnerable to the ozone exposure, especially the ground-level ozone. Such ground-level ozone is formed by the interaction of combustion gases from the vehicles and UV radiation.
• Cataracts in humans.
• Degradation of biopolymers and synthetic polymers, and other clothing materials.

References

• https://www.geeksforgeeks.org/ozone-layer-depletion/#causes-of-ozone-layer-depletion
• Anwar, Fakhra & Nazir, Fahad & Nazeer, Saiqa & Zaman, Noshila & Azam, Saba. (2016). Causes of Ozone Layer Depletion and Its Effects on Human: Review. Atmospheric and Climate Sciences. 06. 129-134. 10.4236/acs.2016.61011
• https://csl.noaa.gov/assessments/ozone/2006/chapters/Q7.pdf

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