Ozone Depletion MCQs Quiz | Class 10

Understanding Ozone Depletion: Causes, Effects, and Prevention

The ozone layer is a vital part of Earth’s stratosphere, acting as a natural shield that absorbs most of the Sun’s harmful ultraviolet (UV) radiation. Without this protective layer, life on Earth would be severely impacted. However, human activities have led to the depletion of this crucial layer, primarily due to the release of certain chemicals into the atmosphere.

Causes of Ozone Depletion

Ozone depletion primarily occurs when human-made chemicals called Ozone-Depleting Substances (ODS) reach the stratosphere. These substances release chlorine and bromine atoms, which then react with and destroy ozone molecules.

• Chlorofluorocarbons (CFCs): Widely used in refrigerants, aerosols, foam blowing agents, and solvents. When released, they slowly rise to the stratosphere where UV radiation breaks them down, releasing chlorine atoms. One chlorine atom can destroy thousands of ozone molecules.
• Halons: Used in fire extinguishers, these compounds contain bromine, which is even more effective at destroying ozone than chlorine.
• Methyl Bromide: An agricultural fumigant, also containing bromine.
• Carbon Tetrachloride and Methyl Chloroform: Industrial solvents that also contribute to ozone depletion.

Here’s a quick look at common ODS and their uses:

Effects of Ozone Depletion

A thinning ozone layer allows more UV-B radiation to reach the Earth’s surface, leading to several adverse effects:

• On Human Health:
  • Skin Cancer: Increased exposure to UV-B radiation is a major risk factor for various types of skin cancer, including melanoma.
  • Cataracts: Prolonged exposure can lead to eye damage, including the formation of cataracts, which can cause blindness.
  • Weakened Immune System: UV-B radiation can suppress the human immune system, making individuals more susceptible to infections and diseases.
• On Ecosystems:
  • Damage to Marine Life: UV-B radiation can harm phytoplankton, the microscopic organisms at the base of the marine food web, leading to reduced fish populations and disruptions in marine ecosystems.
  • Reduced Crop Yields: Increased UV-B can affect plant growth, damaging DNA and inhibiting photosynthesis, thereby reducing crop productivity.
  • Impact on Forests: Some tree species and forest ecosystems are sensitive to UV radiation.
• On Materials:
  • UV-B radiation can degrade synthetic polymers, plastics, and other materials used in outdoor construction and products, leading to shorter lifespans and increased costs.

Prevention of Ozone Depletion (Basic)

The global community has taken significant steps to address ozone depletion, primarily through international agreements and the phasing out of ODS.

• The Montreal Protocol: Signed in 1987, this landmark international treaty successfully aimed to phase out the production and consumption of ODS. It is considered one of the most successful environmental agreements globally.
• Phasing Out ODS: Countries worldwide have committed to replacing CFCs and halons with safer alternatives, such as Hydrofluorocarbons (HFCs), which do not deplete the ozone layer (though some are potent greenhouse gases). Hydrochlorofluorocarbons (HCFCs) were used as transitional substances but are also being phased out due to their ozone-depleting potential.
• Technological Innovation: Development of new, ozone-friendly refrigerants, aerosol propellants, and fire suppression systems.
• Public Awareness and Education: Informing people about the dangers of ozone depletion and encouraging responsible consumption and disposal of products.

Quick Revision List

• Ozone layer is in the stratosphere.
• It protects Earth from harmful UV-B radiation.
• Primary cause of depletion: Chlorofluorocarbons (CFCs) and Halons.
• CFCs release chlorine atoms, Halons release bromine atoms, which destroy ozone.
• Effects: Skin cancer, cataracts, immune system suppression, harm to marine life (phytoplankton), reduced crop yields.
• Key prevention: Montreal Protocol (1987) to phase out ODS.

Extra Practice Questions

1. What is the chemical formula for ozone?
   Answer: O3
2. In which atmospheric layer is “good” ozone primarily found?
   Answer: Stratosphere
3. Name one major international agreement that helped in the recovery of the ozone layer.
   Answer: Montreal Protocol
4. How does increased UV radiation affect marine food webs?
   Answer: It harms phytoplankton, which are at the base of the food web, leading to disruptions.
5. Give one example of an alternative substance used instead of CFCs in refrigeration.
   Answer: Hydrofluorocarbons (HFCs) or Hydrochlorofluorocarbons (HCFCs – transitional)