Ozone Layer is part of Environment and Ecology. Below are notes on 11 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Distinction between Stratospheric (Good) and Tropospheric (Bad) Ozone

  • Tropospheric Ozone (Bad Ozone):
    • Location: Lower atmosphere (troposphere), near ground level.
    • Nature: Harmful air pollutant; secondary pollutant formed by photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs) in sunlight.
    • Impact: Damages human respiratory system, causes eye irritation, harms vegetation, crops, and ecosystems. Potent greenhouse gas contributing to global warming.
    • Ambient Concentration (Good/Acceptable): Concentrations up to 0.06 ppm in ambient air are generally considered acceptable or "good" for public health. Higher levels are considered unhealthy.
  • Stratospheric Ozone (Good Ozone):
    • Location: Upper atmosphere (stratosphere), approximately 10-50 km above Earth's surface.
    • Nature: Naturally occurring; formed when molecular oxygen (O2) absorbs high-energy Ultraviolet (UV) radiation.
    • Impact: Crucial for life on Earth; absorbs harmful UV-B and UV-C radiation from the sun, preventing it from reaching the Earth's surface.
    • Role as GHG: While stratospheric ozone technically is a greenhouse gas and contributes to warming the stratosphere, its primary and most significant role for the protection of life on Earth is UV absorption, not primarily contributing to the global greenhouse effect.
  • Ozone Depletion:
    • Cause: Destruction of stratospheric ozone by Ozone Depleting Substances (ODS) such as Chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform.
    • Consequence: Leads to increased penetration of harmful UV radiation (especially UV-B) to Earth's surface, posing risks to human health (skin cancer, cataracts) and ecosystems.

Ecological and Environmental Consequences of Ozone Depletion (e.g., Marine Ecosystems, Plant Life)

  • Ozone depletion primarily leads to increased penetration of harmful Ultraviolet-B (UV-B) radiation to Earth's surface.
  • Consequences for Plant Life:
    • Inhibits photosynthesis, leading to stunted growth and reduced agricultural yields.
    • Causes DNA damage, affecting plant reproduction, flowering times, and overall productivity.
    • Alters plant physiology and biochemical processes.
  • Consequences for Marine Ecosystems:
    • Damages phytoplankton (base of marine food web), reducing their productivity, growth, and survival rates.
    • Impairs the development and reproduction of marine organisms (e.g., fish larvae, zooplankton, crabs, amphibians) due to DNA damage.
    • Disrupts marine food chains and biogeochemical cycles (e.g., carbon cycle).
  • Other Ecological and Environmental Consequences:
    • Suppression of the human immune system.
    • Increased incidence of skin cancers and cataracts in humans.
    • Damage to DNA and other biomolecules in various life forms.
    • Potential for altered biogeochemical cycles (e.g., nitrogen cycle).

Ecological Significance: Absorption of Ultraviolet (UV) Radiation

  • The ozone layer, primarily located in the stratosphere, protects life on Earth by absorbing harmful solar radiation.
  • Its main ecological significance is the absorption of Ultraviolet (UV) radiation from the Sun.
  • The ozone layer effectively absorbs most UV-B radiation and virtually all UV-C radiation. It also absorbs a small fraction of UVA radiation.
  • UV radiation is classified into three main types based on wavelength:
    • UV-C: Most dangerous; completely absorbed by stratospheric ozone and oxygen (O₂).
    • UV-B: Very harmful; largely absorbed by the ozone layer. Excessive exposure causes skin cancer, cataracts, and immune system suppression.
    • UV-A: Least harmful; largely reaches Earth's surface.
  • Therefore, UV-C rays are considered the most dangerous.
  • The presence of the ozone layer is essential for biotic life as it shields Earth from excessive quantities of high-energy, damaging solar radiation.
  • Depletion of the ozone layer (e.g., the 'ozone hole' discovered over Antarctica) increases our exposure to harmful UV radiation.
  • Ozone depletion is primarily linked to the release of man-made chemicals, notably chlorofluorocarbons (CFCs).

Formation and Natural Balance of Ozone

  • Ozone (O₃) is an allotrope of oxygen, consisting of three oxygen atoms.
  • The ozone layer is primarily found in the stratosphere, mostly at altitudes between 15-55 km.
  • Stratospheric ozone is naturally produced by gaseous chemical reactions, specifically photochemical reactions.
  • Ultraviolet (UV) radiation from sunlight initiates ozone formation:
    • UV radiation (λ < 240 nm) splits molecular oxygen (O₂) into two free oxygen atoms (O).
    • Each free oxygen atom (O) then combines with an oxygen molecule (O₂) to form an ozone molecule (O₃).
  • A natural balance of ozone is maintained through continuous formation and destruction.
  • Ozone is destroyed via photolysis when it absorbs UV radiation, particularly wavelengths less than 320 nm, converting back to O₂ and O.
  • The International Day for the Preservation of the Ozone Layer is observed on September 16th.

Global Monitoring and Assessment of the Ozone Layer Status

  • Ozone layer thickness/concentration is measured in Dobson Units (DU).
  • A Dobson Unit (DU) represents the total amount of ozone in a column of air from the ground to the top of the atmosphere.
  • The instrument used to measure atmospheric ozone concentration is the Dobsonmeter.
  • World Ozone Day is celebrated annually on September 16.

Impacts of Ozone Depletion on Human Health (e.g., Skin Cancer, Cataracts)

  • Ozone layer, primarily in the stratosphere, absorbs most harmful Ultraviolet (UV) radiation (specifically UV-B).
  • Depletion of the ozone layer increases the penetration of harmful UV radiation to Earth's surface.
  • Increased exposure to UV radiation leads to severe human health impacts:
    • Skin Cancers: Significantly increases the incidence of various types, including melanoma and non-melanoma skin cancers.
    • Cataracts: Higher risk of ocular damage, leading to clouding of the eye lens (cataracts).
    • Immune System Suppression: Weakens the human immune system, increasing susceptibility to infections.
    • Other Skin Disorders: Causes premature skin aging, sunburns, and other skin-related ailments.

International Efforts for Ozone Layer Protection: Vienna Convention and Montreal Protocol

Vienna Convention for the Protection of the 1. Ozone Layer (1985): Framework convention for international cooperation on ozone protection. Montreal Protocol on Substances that De2. plete the Ozone Layer (1987): International treaty designed to protect the ozone layer by phasing out the production and consumption of ozone-depleting substances (ODS). Main Objective: Protection of the ozone layer 3. and combating its depletion by restricting production of ODS (e.g., CFCs). Signed: August 1987. 4. Entered into force: January 1, 1989. 5. The discovery of "holes" in the ozone layer 6. became clear in 1985. World Ozone Day / International Day for the 7. Preservation of the Ozone Layer: Celebrated annually on September 16. September 16 commemorates the signing of 8. the Montreal Protocol in 1987. Ozone is considered the protective shield of 9. the Earth against harmful UV radiation.

Mechanism of Ozone Depletion in the Stratosphere

Chlorofluorocarbons (CFCs) and other 1. Ozone Depleting Substances (ODS) like halons, carbon tetrachloride, methyl chloroform, and methyl bromide remain inert in the troposphere. CFCs slowly diffuse into the stratosphere due 2. to their long atmospheric lifetimes. In the stratosphere, powerful ultraviolet (UV) 3. radiation breaks down CFCs, cleaving C-Cl bonds and releasing free radical chlorine (Cl•). Chlorine Catalytic Cycle: 4.

    • A free chlorine radical (Cl•) reacts with ozone (O₃) to form chlorine monoxide radical (ClO•) and oxygen (O₂): `Cl• + O₃ → ClO• + O₂`.
    • Chlorine monoxide radical (ClO•) then reacts with an atomic oxygen (O•) (itself formed from UV photolysis of O₂) to regenerate the free chlorine radical (Cl•) and oxygen (O₂): `ClO• + O• → Cl• + O₂`.
    • The regenerated Cl• continues to react with more O₃, making it a catalyst. One Cl• atom can destroy thousands of O₃ molecules. Nitrogen oxides (NOx) released by superson5. ic jets also deplete stratospheric ozone through similar catalytic reactions. Polar Stratospheric Clouds (PSCs): During 6. polar winters, very low temperatures (< -78°C) lead to the formation of PSCs (ice crystals), which provide surfaces for heterogeneous chemical reactions. PSCs facilitate the conversion of inactive 7. chlorine reservoir species (e.g., hydrogen chloride (HCl) and chlorine nitrate (ClONO₂)) into active, ozone-depleting forms (e.g., molecular chlorine (Cl₂) and hypochlorous acid (HOCl)). When sunlight returns in spring, these active 8. forms are photolyzed to release Cl• radicals, leading to rapid ozone depletion. Polar Vortex: A strong circumpolar wind 9. system that isolates air masses over the poles, trapping ODS and active chlorine. The collapsing or breakup of the polar vortex 10. disperses these ozone-destroying forms of chlorine, which contributes to the stabilization of the ozone layer by reducing localized high concentrations. CFCs have permanent and continuing effects 11. on ozone due to their long atmospheric residence time and the catalytic nature of the destruction process. The Montreal Protocol is an international 12. treaty specifically designed to protect the ozone layer by phasing out the production of ODS (unlike the Kyoto Protocol, which targets Greenhouse Gases).

Ozone Depleting Substances (ODS): Types, Sources, and Characteristics (e.g., CFCs, HCFCs, Halons)

  • Ozone Depleting Substances (ODS) are chemicals that react with stratospheric ozone, leading to its depletion, particularly over Antarctica (forming 'ozone holes').
  • Key ODS Types:
    • Chlorofluorocarbons (CFCs): The primary cause of ozone depletion. They are man-made mixed chlorofluoro-hydrocarbons (e.g., Freons).
    • Halons (Bromofluorocarbons): Contain bromine, significantly more potent in ozone destruction than chlorine.
    • Hydrochlorofluorocarbons (HCFCs): Transitional substitutes for CFCs, less damaging but still ODS.
    • Carbon Tetrachloride (CCl₄): A potent ODS used as an industrial solvent.
    • Methyl Chloroform (1,1,1-trichloroethane): An industrial solvent and ODS.
    • Methyl Bromide: Used as a fumigant.
    • Nitrous Oxide (N₂O): A potent greenhouse gas and significant ODS.
  • Characteristics of ODS (e.g., CFCs):
    • Highly stable in the troposphere, allowing them to reach the stratosphere intact.
    • In the stratosphere, UV radiation breaks them down, releasing reactive chlorine or bromine atoms.
    • These halogen atoms act as catalysts, efficiently destroying thousands of ozone (O₃) molecules.
    • CFCs and many other ODS are also potent greenhouse gases, contributing to climate change and indirectly to increased UV radiation on Earth due to ozone depletion.
  • Sources/Applications of ODS:
    • Refrigerants: Historically, CFCs and HCFCs were used in refrigerators and air conditioners. Modern refrigerators generally avoid ODS.
    • Aerosol propellants: Used in products like perfumes, body sprays, and other aerosols.
    • Foam blowing agents: Used in foam mattresses and insulation.
    • Fire extinguishers: Halons.
    • Solvents: Carbon Tetrachloride, Methyl Chloroform.
    • Fumigants: Methyl Bromide.
    • Primarily originate from anthropogenic activities.
  • Substances NOT typically considered primary ODS or directly responsible for significant ozone depletion: Carbon dioxide (CO₂), Sulphur dioxide (SO₂), Oxygen (O₂), Methane (CH₄ - primarily a greenhouse gas, its role in stratospheric ozone chemistry is indirect/complex, not a direct ODS like halocarbons), Nitrogen dioxide (NO₂), Hydrogen Sulphide, Hydrogen Sulphate, PAN, Pesticides, most Hydrocarbons, Carbon Monoxide (CO).
  • The ozone layer is primarily found in the stratosphere.
  • The total amount of ozone in a column of air from the Earth's surface up to an altitude of 50 km is called 'total column ozone' and is measured in Dobson Units (DU).
  • Ozone layer depletion was first noticed in Antarctica.

Structure and Location of the Stratospheric Ozone Layer

  • Ozone (O3) is a tri-atomic molecule of oxygen.
  • Primarily located in the Earth's stratosphere.
  • Extends roughly from 10 km to 50 km above the Earth's surface.
  • Maximum concentration typically found between 20-30 km altitude, often referred to as the lower portion of the stratosphere.
  • Main function is to absorb most of the Sun's harmful Ultraviolet (UV) radiation (UV-B and UV-C).
  • Ozone layer depletion is a major phenomenon that occurs in the stratosphere.
  • Depletion is primarily caused by Ozone Depleting Substances (ODS) such as Chlorofluorocarbons (CFCs), halons, and carbon tetrachloride.

The Antarctic Ozone Hole: Formation and Dynamics

  • Ozone hole is a region of severe stratospheric ozone depletion over the Antarctic.
  • Primary cause: Chlorofluorocarbons (CFCs) and other Ozone Depleting Substances (ODS).
  • Ozone layer depletion is concentrated in high latitude regions, notably the Antarctic.
  • Major stratospheric ozone hole over Antarctica was discovered in 1985.
  • Formation of the Antarctic ozone hole is due to:
    • Polar Vortex: Strong, stable winds isolating cold air over Antarctica.
    • Polar Stratospheric Clouds (PSCs): Form within the extremely cold polar

6. Forest and Wildlife

Practice MCQs: Ozone Layer

Distinction between Stratospheric (Good) and Tropospheric (Bad) Ozone

  1. Which of the following concentrations of Ozone in ambient air is considered good ?

    Asked in: HPPSC HPAS Prelims 2018

    1. upto 0.06 ppm
    2. upto 0.18 ppm
    3. upto 0.15 ppm
    4. upto 0.20 ppm
    Show answer

    Answer: A. upto 0.06 ppm

    Surface-level ozone is harmful; lower concentrations indicate better air quality. Air quality indices define thresholds for acceptable ozone levels.

  2. व्यापक वायु में ओजोन की Ǔनम्नͧलिͨखत मात्रा में से कौनसी अच्छी मानी जाती है ?

    Asked in: HPPSC HPAS Prelims 2018

    1. 0.06 पीपीएम तक
    2. 0.18 पीपीएम तक
    3. 0.15 पीपीएम तक
    4. 0.20 पीपीएम तक
    Show answer

    Answer: A. 0.06 पीपीएम तक

    The question refers to ground-level ozone, which is a major air pollutant harmful to human health and vegetation. High concentrations of ground-level ozone indicate poor air quality. A "good" amount of ozone in ambient air is a low concentration. Air quality standards typically classify levels up to approximately 0.06 ppm (or 60 parts per billion, ppb) as good or satisfactory. Concentrations significantly higher than this are considered moderate, unhealthy, or very unhealthy.

  3. The incorrect statement about Ozone is : (1) Bad Ozone is present in Troposphere. (2) Ozone is responsible for greenhouse effect in Stratosphere. (3) Ozone is destroyed by chlorofluorocarbons in atmosphere. (4) Ozone shields the surface of the earth from harmful UV-radiation from the sun.

    Asked in: School Lecturer (Sanskrit Edu.) 2018

    1. Bad Ozone is present in Troposphere.
    2. Ozone is responsible for greenhouse effect in Stratosphere.
    3. Ozone is destroyed by chlorofluorocarbons in atmosphere.
    4. Ozone shields the surface of the earth from harmful UV-radiation from the sun.
    Show answer

    Answer: B. Ozone is responsible for greenhouse effect in Stratosphere.

    Statement (1) is correct: "Bad Ozone" or ground- level ozone, which is a pollutant, is primarily found in the troposphere. Statement (2) is incorrect. While ozone does absorb some terrestrial infrared radiation, its primary role in the stratosphere is to absorb UV radiation. The major greenhouse gases responsible for the greenhouse effect are water vapor, carbon dioxide, methane, and nitrous oxide. Ozone plays a minor role, if any, in the stratospheric greenhouse effect compared to its role in UV absorption. Statement (3) is correct: Chlorofluorocarbons (CFCs) and other halocarbons are known to catalytically destroy ozone molecules in the stratosphere. Statement (4) is correct: The ozone layer in the stratosphere absorbs most of the Sun's harmful ultraviolet (UV) radiation, protecting life on Earth.

Ecological and Environmental Consequences of Ozone Depletion (e.g., Marine Ecosystems, Plant Life)

  1. Which of the following are ecological impacts of ozone depletion? (a) Damage human immune system (b) Stunted growth of the plants (c) Rise of temperature (d) Causes cataracts

    Asked in: MPSC CS Prelims 2021

    1. Only (a) and (b)
    2. Only (c) and (d)
    3. Only (b), (c) and (d)
    4. All the above
    Show answer

    Answer: A. Only (a) and (b)

    - Ozone depletion in the stratosphere leads to an increase in harmful UV-B radiation reaching the Earth's surface. - Increased UV-B radiation can damage plant DNA, reduce photosynthesis, and alter plant morphology, leading to stunted growth and reduced biomass (option b). This is a direct ecological impact on primary producers. - UV-B radiation can suppress the immune systems of humans and animals (option a), making them more susceptible to infectious diseases. This is an impact on organisms within the ecosystem. - Increased UV- B radiation causes eye damage like cataracts (option d) and skin damage, including cancer, in humans and animals. These are health impacts on organisms within the ecosystem. - Ozone depletion itself does not directly cause a significant rise in global surface temperature (option c). Greenhouse gases like CO2 are the primary drivers of global warming. Ozone is a greenhouse gas, and its depletion in the stratosphere has a minor cooling effect, while increased tropospheric ozone (a pollutant) has a warming effect. - Considering "ecological impacts" to include effects on organisms within the ecosystem, (a), (b), and (d) are valid impacts of increased UV-B. However, option (c) is incorrect. Given the options, only option A contains two valid impacts ((a) and (b)) and excludes the incorrect one (c). Options B, C, and D include the incorrect statement (c).

  2. The direct effect of Ozone depletion would lead to:

    Asked in: RPSC RAS Prelims 1998

    1. Decrease in yield of plants
    2. Skin cancer
    3. Increase in ultra violet solar radiations
    4. Change in climate
    Show answer

    Answer: C. Increase in ultra violet solar radiations

    The ozone layer in the stratosphere absorbs most of the sun's harmful UV-B radiation. Depletion of this layer means less absorption, leading directly to higher levels of UV-B radiation reaching the ground. The other options (decrease in yield of plants, skin cancer, change in climate) are consequences or indirect effects resulting from increased UV radiation or other related atmospheric changes, not the direct physical effect of ozone depletion itself on radiation levels.

  3. Result of Ozone hole is

    Asked in: WBCS Main Paper 4 2021

    1. greenhouse effect
    2. global warming
    3. acid rain
    4. UV radiations reach the earth
    Show answer

    Answer: D. UV radiations reach the earth

    The stratospheric ozone layer acts as a natural filter, absorbing most of the Sun's biologically damaging UV-B and UV-C radiation. When this layer thins, the absorption is reduced, leading to increased levels of UV radiation reaching the ground.

Ecological Significance: Absorption of Ultraviolet (UV) Radiation

  1. Which rays of ultraviolet are most dangerous ?

    Asked in: CGPSC Prelims Exam 2012

    1. UV A
    2. UV C
    3. UV B
    4. UV D
    Show answer

    Answer: C. UV B

    Ultraviolet (UV) radiation is categorized into three types: UV-A, UV-B, and UV-C. UV-C has the shortest wavelength and highest energy, making it the most dangerous type.

  2. Which of the following protects life on earth from the harmful radiations of the Sun ?

    Asked in: CGPSC Prelims Exam 2013

    1. troposphere
    2. ionosphere
    3. ozone layer
    4. mist
    Show answer

    Answer: C. ozone layer

    The ozone layer is primarily located in the stratosphere. It absorbs most of the Sun's harmful UV-B radiation.

  3. The ultraviolet solar radiations are largely absorbed by

    Asked in: UPSC Geoscientist 2022

    1. carbon dioxide and nitrogen
    2. oxygen and carbon dioxide
    3. oxygen and ozone
    4. nitrogen and ozone
    Show answer

    Answer: C. oxygen and ozone

    - The ozone layer is crucial for life on Earth as it absorbs most of the harmful UV-B and UV-C radiation from the sun. - Absorption of UV-C by oxygen molecules initiates the process of ozone formation (O2 + UV-C -> 2O; O + O2 -> O3).

  4. Direction to the following two questions (Q. Nos. 29 & 30). Read the two statements Assertion (A) & Reason (R). Choose the correct answer from the four choices (a), (b), (c) or (d) as given below : Statement-I (A) : Ozone layer protects the earth from excessive quantities of severely damaging Solar radiation. Statement-II (R) : Ozone hole has been discovered over the Continent of Antarctica.

    Asked in: KPSC KAS Prelims 2014

    1. Both (A) and (R) are correct and (R) explains (A).
    2. Both (A) and (R) are correct, but (R) does not explain (A).
    3. (A) is correct, but (R) is false.
    4. (A) is false, but (R) is true.
    Show answer

    Answer: B. Both (A) and (R) are correct, but (R) does not explain (A).

    Statement (A) is correct because the ozone layer in the stratosphere absorbs most of the sun's harmful ultraviolet-B (UV-B) radiation. Statement (R) is correct as a significant thinning of the ozone layer, often called the ozone hole, was discovered and is most pronounced over Antarctica during the spring months.

  5. The depletion of the ozone layer surrounding our earth increases our exposure to

    Asked in: MPSC CS Prelims 2012

    1. UV radiation
    2. IR radiation
    3. Visible radiation
    4. Microwave radiation
    Show answer

    Answer: A. UV radiation

    The ozone layer in the Earth's stratosphere absorbs most of the Sun's harmful ultraviolet (UV) radiation. Depletion of this layer reduces the amount of UV radiation absorbed, leading to an increase in UV radiation reaching the Earth's surface.

  6. Ozone layer of atmosphere absorbs

    Asked in: TNPSC CS Prelims 2017

    1. Visible radiations
    2. Infrared radiations
    3. Ultraviolet radiations
    4. Radio waves
    Show answer

    Answer: C. Ultraviolet radiations

    The ozone layer (O₃) is primarily located in the stratosphere, about 15-35 kilometers above the Earth's surface. Its crucial function is to absorb a significant portion of the Sun's harmful ultraviolet (UV) radiation, particularly UV-B and UV-C rays. This absorption prevents most of the high-energy UV radiation from reaching the Earth's surface, where it can cause damage to living organisms (like skin cancer, cataracts, and harm to plant life and marine ecosystems).

  7. Which of the following is responsible for protecting humans from harmful ultraviolet rays?

    Asked in: TNPSC CS Prelims 2022

    1. UV-A
    2. UV-C
    3. Ozone layer
    4. None of the above
    Show answer

    Answer: C. Ozone layer

    - The ozone layer is a region of high ozone concentration in the stratosphere, about 15-35 kilometers above the Earth's surface. - Ozone molecules (O₃) effectively absorb UV radiation, preventing most of the highly energetic and damaging wavelengths from reaching the surface. - Exposure to excessive UV radiation can cause skin cancer, cataracts, and harm to the immune system.

  8. Presence of ozone in the atmosphere is important because it absorbs

    Asked in: UPSC CAPF 2017

    1. ultraviolet-A and ultraviolet-B radiations
    2. ultraviolet-B radiations only
    3. infrared-B radiations only
    4. outgoing ultraviolet-B radiations and incoming ultraviolet-A radiations
    Show answer

    Answer: A. ultraviolet-A and ultraviolet-B radiations

    Ozone (O₃) in the stratosphere forms the ozone layer, which is crucial for life on Earth because it absorbs a significant portion of the sun's harmful ultraviolet (UV) radiation before it reaches the surface. While ozone is most effective at absorbing UV-B radiation (wavelengths 280-315 nm), which is particularly harmful to living organisms, it also absorbs a considerable amount of UV-A radiation (315-400 nm) and virtually all UV-C radiation (100-280 nm).

  9. Statement-I : Ozone is essential for biotic life Statement-II : The ozone layer protects the earth's surface from high energy radiation. Select the correct answer from the code given below :

    Asked in: UPPSC Upper Mains 2010

    1. Both (A) and (R) are true and (R) is the correct explanation of (A).
    2. Both (A) and (R) are true, but (R) is not the correct explanation of (A).
    3. (A) is true, but (R) is false.
    4. (A) is false, but (R) is true.
    Show answer

    Answer: A. Both (A) and (R) are true and (R) is the correct explanation of (A).

    Statement-I says Ozone is essential for biotic life. While ground-level ozone is harmful, the ozone layer in the stratosphere is crucial for life on Earth. Statement-II clarifies the essential role: The ozone layer protects the earth's surface from high energy radiation (specifically, most of the sun's harmful ultraviolet (UV) radiation). Without this protection, UV radiation would reach the surface in levels that would cause severe harm to DNA, leading to increased rates of skin cancer, eye damage, and harm to plant and animal life.

Formation and Natural Balance of Ozone

  1. Which one of the following statements with regard to ozone is not correct?

    Asked in: UPSC CDS 2 2020

    1. Ozone is found mostly at 15-55 km in the at‐ mosphere.
    2. Ozone is produced by gaseous chemical reac‐ tions.
    3. 16th November is celebrated as the Interna‐ tional Day for the Preservation of the Ozone Lay‐ er.
    4. Ozone is a form of oxygen in which three oxygen atoms are bounded together.
    Show answer

    Answer: C. 16th November is celebrated as the Interna‐ tional Day for the Preservation of the Ozone Lay‐ er.

    The International Day for the Preservation of the Ozone Layer is celebrated annually on September 16th. This date commemorates the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987.

  2. Ultra-violet radiation from sun light causes the reaction that produce which of the following?

    Asked in: UPPCS Prelims 2018

    1. CO
    2. SO₂
    3. O₃
    4. Fluorides
    Show answer

    Answer: C. O₃

    The formation of stratospheric ozone is a direct photochemical reaction driven by the absorption of ultraviolet radiation from the sun. This process is crucial for absorbing most of the harmful UV-B and UV-C radiation before it reaches the Earth's surface, protecting life.

  3. Ozone undergoes photolysis due to ultra- violet radiations of wavelength ______

    Asked in: WBCS Main Paper 4 2021

    1. <320 nm
    2. <400 nm
    3. <500 nm
    4. <600 nm
    Show answer

    Answer: A. <320 nm

    Ozone (O₃) in the stratosphere absorbs ultraviolet (UV) radiation from the sun, particularly wavelengths shorter than approximately 320 nanometers (nm). This absorption process leads to the photolysis (breakdown by light) of ozone molecules into oxygen (O₂) and atomic oxygen (O).

  4. Ozone layer is mainly made up of :-

    Asked in: Assistant Engineer (AE) Exam 2013

    1. Ozone gas
    2. Carbon dioxide gas
    3. Nitrogen gas
    4. Hydrogen gas
    Show answer

    Answer: A. Ozone gas

    Ozone is a molecule consisting of three oxygen atoms. The ozone layer is a region of higher ozone concentration in the Earth's atmosphere.

  5. Ozone in the upper atmosphere is produced from

    Asked in: Section Officer(LDCE) 2021 22 2021

    1. lightning
    2. electrical appliances on earth
    3. photochemical reaction
    4. electrochemical reaction
    Show answer

    Answer: C. photochemical reaction

    The formation of stratospheric ozone is a result of the interaction between solar ultraviolet radiation and oxygen molecules.

Global Monitoring and Assessment of the Ozone Layer Status

  1. The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of

    Asked in: CGPSC Prelims Exam 2023

    1. Ozone unit
    2. Thomson unit
    3. Dobson units
    4. None of the above
    Show answer

    Answer: C. Dobson units

    A Dobson Unit (DU) is a measure of the total amount of ozone in a vertical column extending from the Earth's surface to the top of the atmosphere. If all the ozone in a column were compressed to standard temperature and pressure (STP), 1 DU would occupy a thickness of 0.01 millimeters. The average amount of ozone in the Earth's atmosphere is about 300 DU.

  2. The instrument used to measure the atmospheric ozone concentration is

    Asked in: TNPSC CS Prelims 2022

    1. Dobsonmeter
    2. Barometer
    3. Hygrometer
    4. Anemometer
    Show answer

    Answer: A. Dobsonmeter

    A Dobsonmeter is the standard ground-based instrument for measuring total column ozone.

  3. Ozone layer thickness is measured in:

    Asked in: MPPSC CS Prelims 2024

    1. Decibels
    2. Dobson units
    3. PPB
    4. PPM
    Show answer

    Answer: B. Dobson units

    Dobson Units are the standard unit of measurement for the total amount of ozone in a vertical column of the atmosphere.

  4. Ozone day is _____

    Asked in: WBCS Main Paper 4 2021

    1. January 30
    2. September 16
    3. April 21
    4. December 25
    Show answer

    Answer: B. September 16

    The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production and consumption of ozone-depleting substances.

  5. Dobson unit is used to measure which one of the following?

    Asked in: Assistant Conservator of Forest Exam 2019

    1. Thickness of Ozone layer.
    2. Pesticide contamination in water.
    3. Aerosol concentration in atmospheric column.
    4. None of these.
    Show answer

    Answer: A. Thickness of Ozone layer.

    This question tests the knowledge of specific units of measurement used in environmental science, particularly related to atmospheric composition.

  6. Dobson Unit (DU) is used to measure the following :

    Asked in: Co operative Supervisor & Environment Supervisor (Group C) Exam 2023

    1. Depth of sea
    2. Thickness of rocks
    3. Ozone layer
    4. None of these
    Show answer

    Answer: C. Ozone layer

    Dobson Units are a convenient way to quantify the total amount of ozone in a vertical column above a specific location on the Earth's surface.

  7. Which one among the following is measured by Dobson unit?

    Asked in: RO ARO Mains 2021

    1. Ozone concentration
    2. Thermal conductivity
    3. Soil moisture
    4. Radiation
    Show answer

    Answer: A. Ozone concentration

    Dobson unit is used to measure ozone concentration.

Impacts of Ozone Depletion on Human Health (e.g., Skin Cancer, Cataracts)

  1. In coming years, skin related disorders will become more common due to :

    Asked in: HPPSC HPAS Prelims 2011 · WBCS Main Paper 4 2022

    1. Excessive use of detergents
    2. Water pollution
    3. Air pollution
    4. Depletion of ozone layer
    Show answer

    Answer: D. Depletion of ozone layer

    Depletion of the stratospheric ozone layer allows more ultraviolet (UV) radiation, particularly UV-B, to reach the Earth's surface. Increased exposure to UV-B radiation is a major risk factor for various skin disorders, including skin cancers (melanoma and non-melanoma), premature aging of the skin, and other skin damage. While other factors can contribute to skin issues, the projected increase in severe disorders like skin cancer is most directly linked to ozone depletion and resultant increased UV radiation.

  2. Directions : The following five (5) items consist of two statements, Statement I and Statement II. Examine these two statements carefully and select the correct answer using the code given below. Statement I : 32. Skin cancer is generally caused by the ultraviolet radiation. Statement II : Stratosphere allows ultraviolet radiation to enter the earth from the sun.

    Asked in: UPSC CDS 2 2017

    1. Both the statements are individually true and Statement II is the correct explanation of Statement I
    2. Both the statements are individually true but Statement II is not the correct explanation of Statement I
    3. Statement I is true but Statement II is false
    4. Statement I is false but Statement II is true
    Show answer

    Answer: C. Statement I is true but Statement II is false

    - Statement I: Skin cancer is indeed generally caused by excessive exposure to ultraviolet (UV) radiation from the sun or artificial sources like tanning beds. - Statement II: The stratosphere, particularly the ozone layer within it, acts as a shield that absorbs most of the harmful UV-B and UV-C radiation from the sun, preventing it from reaching the Earth's surface. Therefore, the stratosphere does not allow harmful UV radiation to enter; it blocks it.

  3. Which one of the following pairs is correctly matched?

    Asked in: UPPCS Prelims 2015

    1. Sulphur dioxide — Teeth
    2. Fluoride pollution — Bhopal gas tragedy
    3. Methyl isocyanate — Acid rain
    4. Ozone depletion — Skin cancer
    Show answer

    Answer: D. Ozone depletion — Skin cancer

    The stratospheric ozone layer absorbs most of the Sun's UV radiation. Its thinning (depletion) allows more UV-B rays to penetrate, increasing health risks like skin cancer and cataracts.

International Efforts for Ozone Layer Protection: Vienna Convention and Montreal Protocol

  1. Montreal protocol is related with

    Asked in: CGPSC Prelims Exam 2015

    1. To protect the Ozone layer depletion
    2. Global warming
    3. Acid rain
    4. Photochemical smog
    Show answer

    Answer: A. To protect the Ozone layer depletion

    The primary objective of the Montreal Protocol is the protection of the stratospheric ozone layer.

  2. Montreal Protocol ratifies:

    Asked in: UPSC Geoscientist 2021

    1. restricting the production of CFCs.
    2. sustainable development.
    3. carbon trading.
    4. restricting the global average temperature below 2 °C above the pre-industrial level.
    Show answer

    Answer: A. restricting the production of CFCs.

    Ratified in 1987, the Montreal Protocol is considered one of the most successful international environmental agreements. Its implementation has led to a significant reduction in the emission of ODS and the slow recovery of the ozone layer.

  3. World Ozone Day is celebrated on:

    Asked in: HPPSC HPAS Prelims 2014 · UPPCS Prelims 2021

    1. June 19
    2. August 19
    3. September 16
    4. November 19
    Show answer

    Answer: C. September 16

    - The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production and consumption of ozone-depleting substances (ODS). - World Ozone Day is used to raise awareness about the importance of the ozone layer and the success of the Montreal Protocol.

  4. ͪवश्व ओज़ोन Ǒदवस मनाया जाता है :

    Asked in: HPPSC HPAS Prelims 2014

    1. 19 जून को
    2. 19 अगस्त को
    3. 16 lसतम्बर को
    4. 19 नविम्बर को
    Show answer

    Answer: C. 16 lसतम्बर को

    World Ozone Day is celebrated annually on September 16th to commemorate the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer.

  5. Which of the following days is designated as World Ozone Day by the U.N. General Assembly ?

    Asked in: MPSC CS Prelims 2018

    1. 1st June
    2. 5th June
    3. 1st September
    4. 16th September
    Show answer

    Answer: D. 16th September

    The United Nations General Assembly proclaimed 16 September as the International Day for the Preservation of the Ozone Layer, commemorating the date in 1987 when the Montreal Protocol on Substances that Deplete the Ozone Layer was signed.

  6. In relation to Ozone which statements are true ?

    Asked in: MPSC CS Prelims 2023

    1. Ozone is called protection shield of the Earth.
    2. In 1985 it was clear that Ozone layer has holes.
    3. 16th September is celebrated as World Ozone Day.
    4. In 1989 chemicals responsible for Ozone depletion are banned to utilize. A. Only A, B and C B. Only B, C and D C. Only A, C and D D. All the above
    Show answer

    Answer: D. In 1989 chemicals responsible for Ozone depletion are banned to utilize. A. Only A, B and C B. Only B, C and D C. Only A, C and D D. All the above

    A. The stratospheric ozone layer absorbs most of the sun's harmful ultraviolet (UV) radiation, protecting life on Earth. B. The scientific paper reporting the discovery of the Antarctic ozone hole by Farman, Gardiner, and Shanklin was published in Nature in May 1985. C. September 16th is internationally recognized as World Ozone Day, marking the date the Montreal Protocol on Substances that Deplete the Ozone Layer was signed in 1987. D. The Montreal Protocol, which came into effect in 1989, is an international treaty designed to phase out the production and consumption of ozone-depleting substances (ODS) such as CFCs and HCFCs.

  7. When is the ‘World Ozone Day’ celebrated ?

    Asked in: UKPSC CS Prelims 2021

    1. 25th December
    2. 21st April
    3. 16th September
    4. 30th January
    Show answer

    Answer: C. 16th September

    - This day commemorates the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987. - The Montreal Protocol is a landmark international treaty designed to protect the ozone layer by phasing out the production and consumption of ozone-depleting substances (ODS).

  8. On which date Ozone Day is observed?

    Asked in: UPPCS Prelims 2022

    1. October 2
    2. September 16
    3. April 29
    4. January 30
    Show answer

    Answer: B. September 16

    This date commemorates the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987.

  9. Which one of the following is the main objective of Vienna Convention and Montreal Protocol ?

    Asked in: UPSC CAPF 2019

    1. Combat desertification
    2. Formulate sustainable developmental goals
    3. Protection of ozone layer
    4. Combat climate change
    Show answer

    Answer: C. Protection of ozone layer

    Identifying the key international environmental agreements and their primary focus is important. The Vienna Convention and Montreal Protocol are landmark agreements solely focused on protecting the stratospheric ozone layer.

Mechanism of Ozone Depletion in the Stratosphere

  1. Consider the following statements about Chlorofluorocarbons (CFCs) : 1. CFCs remain inert in the troposphere but slowly diffuse into the stratosphere. 2. CFCs in the upper atmosphere are subjected to UV radiations, generating free radical chlorine that immediately reacts with O₃ to form a radical called chlorine monoxide (ClO). 3. Each ClO can initiate a series of chemical reactions, leading to the destruction of the ozone layer. How many of the statements given above is/are correct ?

    Asked in: UPSC Geoscientist 2024

    1. 1
    2. 2
    3. 3
    4. None
    Show answer

    Answer: C. 3

    - Statement 1 is correct: Chlorofluorocarbons (CFCs) are very stable in the lower atmosphere (troposphere) and do not easily react or break down. Over time, they slowly migrate upwards through diffusion into the stratosphere. - Statement 2 is correct: Once in the upper atmosphere (stratosphere), CFC molecules are exposed to high-energy ultraviolet (UV) radiation from the sun, which breaks the carbon-chlorine bond, releasing highly reactive free radical chlorine atoms (Cl•). A chlorine radical then reacts with an ozone molecule (O₃) to form chlorine monoxide (ClO•) and oxygen (O₂). - Statement 3 is correct: The chlorine monoxide radical (ClO•) is also highly reactive. It can react with a free oxygen atom (O) (which is naturally present in the stratosphere from the breakdown of O₃) to form another chlorine radical (Cl•) and oxygen (O₂). The regenerated chlorine radical can then attack another ozone molecule, continuing the cycle. This chain reaction allows a single chlorine atom to destroy many thousands of ozone molecules before it is eventually removed from the stratosphere by other processes. This catalytic cycle leads to significant depletion of the ozone layer.

  2. On the ozone layer, the CFC has continuing their effects as :

    Asked in: OPSC CS Prelims 2021

    1. Reactions use up the Cl atoms formed by them leading to the degradation of ozone.
    2. Their efficient absorption by water vapours of the atmosphere.
    3. In reactions, the Cl atoms formed by them serve as catalysts leading to the degradation of ozone.
    4. They are constantly produced in increasing quantities, globally.
    Show answer

    Answer: C. In reactions, the Cl atoms formed by them serve as catalysts leading to the degradation of ozone.

    Chlorofluorocarbons (CFCs) are stable in the lower atmosphere. However, when they reach the stratosphere, they are broken down by ultraviolet (UV) radiation from the sun, releasing chlorine atoms (Cl). These free chlorine atoms then act as catalysts in a chain reaction that destroys ozone molecules (O₃). A single chlorine atom can destroy thousands of ozone molecules before it is removed from the stratosphere.

  3. Collapsing of polar vortex contributes to the stabilization of the ozone layer because it :

    Asked in: TSPSC Group 1 Prelims 2024

    1. Allows ozone depleting chemicals to accu‐ mulate
    2. Disperses ozone-destroying forms of chlor‐ ine
    3. Accelerates ozone depletion reactions
    4. Triggers the release of additional chlorine into the stratosphere
    Show answer

    Answer: B. Disperses ozone-destroying forms of chlor‐ ine

    A stable and cold polar vortex isolates air, allowing the formation of Polar Stratospheric Clouds (PSCs). Reactions on PSCs activate inert chlorine compounds into ozone-depleting forms. The vortex also prevents mixing with ozone-rich air. When the vortex collapses, the isolated, chlorine-activated air mixes with air from lower latitudes, diluting the concentration of activated chlorine. Warmer temperatures also deactivate chlorine. This dispersion and deactivation reduce the rate of ozone depletion.

  4. Which of the following processes would explain ozone losses in the atmosphere? When ozone is exposed to 1. CFCs and UV radiation. 2. long winter circumpolar winds to form ice crystals. 3. singlet oxygen atom and chlorine monoxide. Select the correct answer using the code given below :

    Asked in: UPSC CAPF 2011

    1. 1, 2 and 3
    2. 2 and 3 only
    3. 1 and 2 only
    4. 1 and 3 only
    Show answer

    Answer: A. 1, 2 and 3

  5. CFCs (and other halogenated hydrocarbons like halons) are transported to the stratosphere where UV radiation breaks them down, releasing reactive chlorine and bromine atoms. These halogen atoms catalyze the destruction of ozone (O3). Thus, statement 1 is correct. 2. In polar regions during winter, extremely cold temperatures and the presence of the polar vortex (circumpolar winds) lead to the formation of Polar Stratospheric Clouds (PSCs), which can consist of ice crystals or nitric acid particles. These clouds provide surfaces for heterogeneous chemical reactions that convert less reactive halogen compounds into highly reactive forms (like Cl2). When sunlight returns in spring, these reactive forms are photolyzed, releasing large amounts of chlorine and bromine atoms, leading to rapid ozone depletion (the ozone hole). Thus, statement 2 is correct. 3. Ozone destruction primarily occurs through catalytic cycles involving reactive species. A key cycle involves chlorine monoxide (ClO) and oxygen atoms (O). Chlorine atoms react with ozone (Cl + O3 -> ClO + O2). Chlorine monoxide then reacts with an oxygen atom (ClO + O -> Cl + O2), regenerating the chlorine atom. The oxygen atoms (O) in the stratosphere are formed by the photolysis of oxygen molecules (O2) by UV light; these can be in ground (triplet) or excited (singlet) states, and both react with ClO. Thus, statement 3 refers to the reactive intermediates and partners involved in the catalytic destruction cycle and is correct. 57. Depletion of the stratospheric ozone layer occurs when molecules of ozone are destroyed by chemicals such as

    Asked in: WBCS Main Paper 4 2022

    1. CFC
    2. DDT
    3. O₃
    4. PCB
    Show answer

    Answer: A. CFC

    CFCs (Chlorofluorocarbons) are major chemicals responsible for ozone depletion in the stratosphere.

  6. The supersonic jets cause pollution by the thinning of

    Asked in: WBCS Main Paper 4 2022

    1. O₂ layer
    2. O₃ layer
    3. CO₂ layer
    4. SO₂ layer
    Show answer

    Answer: B. O₃ layer

    The ozone layer is located primarily in the lower portion of the stratosphere and absorbs most of the Sun's harmful ultraviolet (UV) radiation. Depletion of the ozone layer allows more UV radiation to reach the Earth's surface, which can cause harm to living organisms. Nitrogen oxides, such as nitric oxide (NO) and nitrogen dioxide (NO₂), can react with ozone, breaking it down.

  7. Statement (A) : Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen molecule. Statement (B) : The decrease in ozone has been linked to synthetic chemicals like chloro-fluoro-carbons (CFCs). - Question not attempted

    Asked in: Deputy Jailor 2024

    1. Both statements (A) and (B) are correct.
    2. Both statements (A) and (B) are incorrect.
    3. Statement (A) is correct, but (B) is incor‐ rect.
    4. Statement (A) is incorrect, but (B) is cor‐ rect.
    Show answer

    Answer: A. Both statements (A) and (B) are correct.

    Statement (A) describes the photochemical formation of ozone in the stratosphere. Statement (B) describes the cause of ozone depletion, which is primarily attributed to anthropogenic chemicals like CFCs.

  8. Select the incorrect statement from the following - (1) In stratosphere chlorine atoms are released from Chlorofluorocarbons (CFCs) by UV rays. (2) Chlorofluorocarbons (CFCs) added to the stratosphere, have permanent and continuing effects on Ozone. (3) The ‘Kyoto protocol’ is for the substances that deplete Ozone layers. (4) In stratosphere, chlorine atoms act as a catalyst for degrading ozone.

    Asked in: Head Master Praveshika School (Sanskrit Edu.) 2021

    1. (1)
    2. (2)
    3. (3)
    4. (4)
    Show answer

    Answer: C. (3)

    The Kyoto Protocol deals with reducing greenhouse gas emissions to combat climate change. The Montreal Protocol is the treaty aimed at protecting the ozone layer by regulating ozone- depleting substances like CFCs.

Ozone Depleting Substances (ODS): Types, Sources, and Characteristics (e.g., CFCs, HCFCs, Halons)

  1. Which one is responsible for Ozone holes ?

    Asked in: CGPSC Prelims Exam 2014

    1. CO₂
    2. SO₂
    3. O₂
    4. CFC
    Show answer

    Answer: D. CFC

    Ozone holes, referring to the depletion of the stratospheric ozone layer, are primarily caused by the release of man-made chemicals containing chlorine and bromine. Chlorofluorocarbons (CFCs) are a major class of such ozone-depleting substances (ODS). When CFCs reach the stratosphere, UV radiation breaks them down, releasing chlorine atoms which catalytically destroy ozone molecules (O₃). CO₂ is a greenhouse gas affecting climate change, SO₂ contributes to acid rain and air pollution, and O₂ is atmospheric oxygen, none of which are responsible for ozone depletion.

  2. Which of the following is not an ozone depleting substance?

    Asked in: GPSC Prelims CSP 2 2019

    1. Nitrous oxide
    2. Bromine oxide
    3. Sulphur dioxide
    4. None of the above
    Show answer

    Answer: C. Sulphur dioxide

    ODS primarily contain chlorine or bromine, which catalyze the destruction of stratospheric ozone.

  3. Freons cause great environmental damage. They are :

    Asked in: HPPSC HPAS Prelims 2010

    1. Mixed carbon gases
    2. Mixed chlorofluoro-hydrocarbons
    3. Mixed sulphur gases
    4. Free gases
    Show answer

    Answer: B. Mixed chlorofluoro-hydrocarbons

    Freons are a group of chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) compounds. These are organic compounds that contain carbon, fluorine, and chlorine atoms, and often hydrogen atoms (in HCFCs).

  4. Which of the above statements are correct? A) B) C) D) Methane and Carbon Tetrachloride () are responsible for ozone depletion.

    Asked in: KPSC KAS Prelims 2024

    1. (1) only
    2. (2) only
    3. (3) only
    4. (4) only
    Show answer

    Answer: D. (4) only

    Carbon Tetrachloride (CCl4) is a known and potent ozone-depleting substance (ODS), listed under the Montreal Protocol. Methane (CH4), however, is primarily a greenhouse gas and not considered a major direct ozone-depleting substance in the same way as halogenated compounds like CCl4, CFCs, and Halons. Its indirect effects on stratospheric ozone chemistry are complex.

  5. The main gas responsible for ozone depletion is :

    Asked in: MPSC CS Prelims 2014

    1. Carbon dioxide
    2. Nitrogen dioxide
    3. Methane
    4. Chloro fluro carbon
    Show answer

    Answer: D. Chloro fluro carbon

    Ozone depletion, particularly in the stratosphere, is a significant environmental issue caused by certain man-made chemicals that release halogen atoms (chlorine, bromine) when they break down.

  6. Match the following with correct options. (a) Inexhaustible re‐ (i) Anthropogenic activitsources ies (ii) Fossil fuels like coal (b) Stratosphere and petrol (iii) Solar Energy (c) Non-renewable resources (d) Chlorofluorocar‐ (iv) Rich layer of Ozone bons

    Asked in: MPSC CS Prelims 2020

    1. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
    2. (a)-(iv), (b)-(ii), (c)-(iii), (d)-(i)
    3. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
    4. (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
    Show answer

    Answer: C. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)

    - Inexhaustible resources are renewable and unlimited (e.g., solar energy). - The stratosphere contains the protective ozone layer. - Non-renewable resources are finite and depletable (e.g., fossil fuels). - Chlorofluorocarbons are synthetic compounds produced by humans (anthropogenic).

  7. Ozone layer in the stratosphere is affected by the increase in the atmospheric concentration of :

    Asked in: OPSC CS Prelims 2017

    1. CO₂
    2. NH₃
    3. SO₂
    4. CFC
    Show answer

    Answer: D. CFC

    Chlorofluorocarbons (CFCs) are the primary chemicals responsible for the depletion of the stratospheric ozone layer. When CFCs reach the stratosphere, they are broken down by UV radiation, releasing chlorine atoms which catalytically destroy ozone molecules.

  8. The major cause for the depletion of Ozone is

    Asked in: TNPSC CS Prelims 2021

    1. Aerosol
    2. Hydrogen Sulphide
    3. Hydrogen Sulphate
    4. Carbon di oxide
    Show answer

    Answer: A. Aerosol

    The depletion of the ozone layer is primarily caused by human-produced chemicals known as Ozone- Depleting Substances (ODS), such as Chlorofluorocarbons (CFCs) and Halons. CFCs were widely used as propellants in aerosol spray cans, refrigerants, and in foam blowing. While 'Aerosol' itself is a physical state (particles suspended in gas), its use as propellants for products containing ODS like CFCs made aerosols a significant contributor to ozone depletion before these substances were phased out.

  9. The depletion in atmospheric ozone layer in last century was due to :

    Asked in: UPSC CAPF 2023

    1. chlorofluorocarbon
    2. carbon monoxide
    3. methane
    4. pesticides
    Show answer

    Answer: A. chlorofluorocarbon

    - CFCs and other ozone-depleting substances (ODS) like halons, carbon tetrachloride, and methyl chloroform were widely used in refrigerants, aerosols, fire extinguishers, and solvents. - When these chemicals reach the stratosphere, they are broken down by ultraviolet radiation, releasing chlorine and bromine atoms which catalytically destroy ozone molecules ($\text{O}_3$).

Structure and Location of the Stratospheric Ozone Layer

  1. Ozone layer, which absorbs the ultra-violet radiation, is found in which one of the following layers of the atmosphere ?

    Asked in: UPSC CDS 1 2021

    1. Ionosphere
    2. Troposphere
    3. Mesosphere
    4. Stratosphere
    Show answer

    Answer: D. Stratosphere

    - The atmosphere is divided into several layers: Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere. - Each layer has distinct characteristics regarding temperature profile and composition.

  2. Statement I : Ozone is a tri-atomic molecule of oxygen. Statement II : Ozone is mainly concentrated in stratosphere.

    Asked in: UPSC NDA 2 2016

    1. Both the statements are individually true and Statement II is the correct explanation of Statement I
    2. Both the statements are individually true but Statement II is not the correct explanation of Statement I
    3. Statement I is true but Statement II is false
    4. Statement I is false but Statement II is true
    Show answer

    Answer: B. Both the statements are individually true but Statement II is not the correct explanation of Statement I

    - Ozone (O3) is a molecule composed of three oxygen atoms. This is its chemical structure. - The ozone layer, where most atmospheric ozone is found, is located primarily in the stratosphere, about 15-35 km above the Earth's surface.

  3. The maximum concentration of Ozone is found in which of the following?

    Asked in: UPPCS Prelims 2018

    1. Troposphere
    2. Mesosphere
    3. Stratosphere
    4. Exosphere
    Show answer

    Answer: C. Stratosphere

    The maximum concentration of ozone is found in the stratosphere, specifically in a region often referred to as the ozone layer, located approximately 15 to 35 kilometers above the Earth's surface. This layer absorbs most of the Sun's ultraviolet (UV) radiation.

  4. Which of the following paris is NOT correctly matched?

    Asked in: UPPCS Prelims 2018

    1. Renneting-Cheese
    2. Genetic Engineering-Plasmids
    3. Golden rice-Vitamin A
    4. Ozone layer-Troposphere
    Show answer

    Answer: D. Ozone layer-Troposphere

    The Earth's atmosphere is divided into distinct layers based on temperature profiles and composition. The stratosphere is the layer above the troposphere, and it is where the majority of atmospheric ozone is concentrated, forming the ozone layer.

  5. Ozone layer depletion is a major phenomenon in :

    Asked in: UPSC CAPF 2015

    1. Troposphere
    2. Stratosphere
    3. Thermosphere
    4. Exosphere
    Show answer

    Answer: B. Stratosphere

    The Earth's atmosphere is divided into several layers: Troposphere (lowest), Stratosphere, Mesosphere, Thermosphere, and Exosphere (highest). The ozone layer resides primarily within the stratosphere.

  6. Identify the correct statements from the following and select the correct answer using the code given below : I. Ozone layer exists in the lower portion of the earth's stratosphere. II. Ozone layer acts as sunscreens against the sun's ultraviolet radiations. III. The first ozone layer was discovered over Antarctica in 1985. IV. Chlorofluorocarbons (CFCs), halons, carbon tetrachloride, etc. are ozone depleting substances.

    Asked in: Asst Mana APDCL GS 06 2023

    1. I and II
    2. II and III
    3. I, II and IV
    4. All statements are correct
    Show answer

    Answer: C. I, II and IV

    The ozone layer's location in the stratosphere and its function as a UV shield are fundamental concepts. Understanding the historical context of ozone hole discovery and identifying common ozone-depleting substances are also crucial.

The Antarctic Ozone Hole: Formation and Dynamics

  1. Ozone hole is a region over :

    Asked in: UPSC CDS 2 2024

    1. the Antarctic caused mainly by CFC gases.
    2. the Antarctic caused mainly by carbon dioxide gas.
    3. the Arctic caused mainly by CFC gases.
    4. the Arctic caused mainly by carbon dioxide gas.
    Show answer

    Answer: A. the Antarctic caused mainly by CFC gases.

    The "ozone hole" refers to the dramatic thinning of the stratospheric ozone layer that occurs annually over Antarctica during the Southern Hemisphere spring (August-October). This severe depletion is primarily driven by catalytic reactions involving chlorine and bromine atoms released from synthetic ozone-depleting substances (ODS) like chlorofluorocarbons (CFCs) and halons, which accumulate in the stratosphere and are activated under the extremely cold conditions and sunlight present in the Antarctic polar vortex.

  2. Ozone layer depletion is concentrated in:

    Asked in: UPSC Geoscientist 2020

    1. mid-latitude regions.
    2. high latitude regions.
    3. equatorial regions.
    4. tropical regions.
    Show answer

    Answer: B. high latitude regions.

    - Ozone depletion is concentrated at the poles. - This phenomenon is driven by chemical reactions involving ozone-depleting substances (like CFCs) which are catalyzed on the surface of polar stratospheric clouds (PSCs) that form at very low temperatures in the polar stratosphere during winter. - The depletion becomes pronounced in spring when sunlight returns, initiating the catalytic cycles.

  3. Which one among the following is true about Ozone Hole?

    Asked in: UPSC Geoscientist 2021

    1. It is the loss of Tropospheric ozone over Ant‐ arctica
    2. It is the loss of Stratospheric ozone over Ant‐ arctica
    3. It is a hole in the Antarctic ice sheet created due to ozone
    4. It is the loss of equatorial ozone
    Show answer

    Answer: B. It is the loss of Stratospheric ozone over Ant‐ arctica

    The stratospheric ozone layer absorbs most of the Sun's harmful ultraviolet (UV) radiation. Its depletion, mainly due to human-produced chemicals like CFCs and halons, leads to increased UV radiation reaching the Earth's surface.

  4. The major stratospheric ozone layer over Antarctica was discovered in _____.

    Asked in: WBCS Main Paper 4 2021

    1. 1983
    2. 1985
    3. 1987
    4. 1980
    Show answer

    Answer: B. 1985

    Scientists from the British Antarctic Survey (Joe Farman, Brian Gardiner, and Jonathan Shanklin) first published their findings on significant ozone depletion over Antarctica in the journal Nature in May 1985, based on their ground-based measurements dating back several years. This discovery drew global attention to the issue of ozone depletion.

  5. The formation of ozone hole in the Antarctic region has been a cause of concern. What could be the reason for the formation of this hole?

    Asked in: WBCS Main Paper 4 2022

    1. Presence of prominent tropospheric turbu‐ lence; and inflow of CFCs.
    2. Presence of prominent polar front and strato‐ spheric clouds; and inflow of CFCs.
    3. Absence of polar front and stratospheric clouds; and inflow of methane and CFCs.
    4. Increased temperature at polar region due to global warming.
    Show answer

    Answer: B. Presence of prominent polar front and strato‐ spheric clouds; and inflow of CFCs.

    The key factors are the formation of the polar vortex, extremely low stratospheric temperatures leading to the formation of Polar Stratospheric Clouds (PSCs), and the presence of CFCs and their breakdown products. PSCs provide surfaces for chemical reactions that convert inactive chlorine compounds into active forms (like ClO) which catalytically destroy ozone when sunlight returns after