Ozone Layer

1. Which one of the following is associated with the issue of control and

Which one of the following is associated with the issue of control and phasing out of the use of ozone-depleting substances?

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Bretton Woods Conference
Montreal Protocol
Kyoto Protocol
Nagoya Protocol
This question was previously asked in
UPSC IAS – 2015
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The Montreal Protocol is associated with the issue of control and phasing out of the use of ozone-depleting substances.
The Montreal Protocol on Substances that Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production and consumption of ozone-depleting substances (ODS), such as chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform. It was signed in 1987 and has been successful in reducing the atmospheric concentration of ODS.
– **Bretton Woods Conference (1944):** Established the International Monetary Fund (IMF) and the International Bank for Reconstruction and Development (IBRD, now part of the World Bank Group), focusing on international monetary and financial regulation.
– **Kyoto Protocol (1997):** An international treaty which extends the 1992 United Nations Framework Convention on Climate Change (UNFCCC) that commits state parties to reduce greenhouse gas emissions.
– **Nagoya Protocol (2010):** An international agreement aiming at sharing the benefits arising from the utilization of genetic resources in a fair and equitable way. It is a supplementary agreement to the Convention on Biological Diversity (CBD).

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

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

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chlorofluorocarbon
carbon monoxide
methane
pesticides
This question was previously asked in
UPSC CAPF – 2023
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The correct answer is A. The depletion of the stratospheric ozone layer observed in the last century is primarily attributed to the release of synthetic chemicals, especially chlorofluorocarbons (CFCs).
– 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 ($\text{O}_3$).
The discovery of the ozone hole over Antarctica and subsequent scientific research led to the Montreal Protocol on Substances that Deplete the Ozone Layer (1987), an international treaty designed to phase out the production and consumption of ODS. This has led to a slow recovery of the ozone layer. Carbon monoxide, methane, and pesticides have different environmental impacts but are not the primary cause of stratospheric ozone depletion.

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3. Which one of the following is the main objective of Vienna Convention

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

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Combat desertification
Formulate sustainable developmental goals
Protection of ozone layer
Combat climate change
This question was previously asked in
UPSC CAPF – 2019
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The Vienna Convention for the Protection of the Ozone Layer (1985) and its subsequent Montreal Protocol on Substances that Deplete the Ozone Layer (1987) were specifically established to address the depletion of the Earth’s ozone layer. Their main objective is to phase out the production and consumption of ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs) and halons.
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.
While ozone depletion and climate change are linked (some ODS are also potent greenhouse gases), the direct objective of the Montreal Protocol was ozone protection. Combating desertification is the focus of the UN Convention to Combat Desertification (UNCCD). Sustainable Developmental Goals (SDGs) are a broader framework for global development. Combating climate change is the focus of the UNFCCC (United Nations Framework Convention on Climate Change) and agreements like the Kyoto Protocol and Paris Agreement.

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

Presence of ozone in the atmosphere is important because it absorbs

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ultraviolet-A and ultraviolet-B radiations
ultraviolet-B radiations only
infrared-B radiations only
outgoing ultraviolet-B radiations and incoming ultraviolet-A radiations
This question was previously asked in
UPSC CAPF – 2017
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The correct answer is 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).
UV-A radiation is less harmful than UV-B but can still cause skin damage and premature aging. UV-B radiation is the primary cause of sunburn, skin cancer, and cataracts. UV-C radiation is the most energetic and harmful but is completely absorbed by the ozone layer and oxygen in the atmosphere. Therefore, the presence of stratospheric ozone is important for absorbing both UV-A and UV-B, reducing their intensity at the Earth’s surface.

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5. Ozone layer depletion is a major phenomenon in :

Ozone layer depletion is a major phenomenon in :

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Troposphere
Stratosphere
Thermosphere
Exosphere
This question was previously asked in
UPSC CAPF – 2015
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The ozone layer is a region of Earth’s stratosphere that absorbs most of the Sun’s ultraviolet (UV) radiation. Ozone (O₃) concentration is highest in the lower portion of the stratosphere, from about 15 to 35 kilometers above Earth’s surface, although it is present in small quantities throughout the atmosphere. Ozone depletion, primarily caused by human-produced ozone-depleting substances like chlorofluorocarbons (CFCs), is a significant phenomenon occurring within the 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.
While the stratosphere is where beneficial ozone is found and depleted, ozone is also present in the troposphere. Tropospheric ozone is a key component of smog and is considered a harmful air pollutant and a greenhouse gas, but it does not form a “layer” in the same way as stratospheric ozone and is not where the major depletion phenomenon occurs.

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6. Which of the following processes would explain ozone losses in the atm

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 :

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1, 2 and 3
2 and 3 only
1 and 2 only
1 and 3 only
This question was previously asked in
UPSC CAPF – 2011
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All three listed processes contribute to ozone losses in the atmosphere.
1. 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.
The processes described in statements 1, 2, and 3 collectively explain how human-produced substances like CFCs lead to significant ozone depletion, particularly pronounced over the polar regions due to the unique meteorological conditions that facilitate the reactions on PSCs.

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7. Statement I : Ozone is a tri-atomic molecule of oxygen. Statement II :

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

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Both the statements are individually true and Statement II is the correct explanation of Statement I
Both the statements are individually true but Statement II is not the correct explanation of Statement I
Statement I is true but Statement II is false
Statement I is false but Statement II is true
This question was previously asked in
UPSC NDA-2 – 2016
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Statement I: Ozone is a tri-atomic molecule of oxygen. (True)
Statement II: Ozone is mainly concentrated in stratosphere. (True)
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.
– Statement I describes the chemical composition of an ozone molecule. Statement II describes the primary location of ozone in the atmosphere.
– The location of ozone in the stratosphere is due to its formation process, which involves the photolysis of oxygen molecules (O2) by UV radiation, followed by the combination of resulting oxygen atoms with O2. This process is most efficient in the stratosphere. However, this does not explain *why* the molecule itself has three atoms. The fact that it is tri-atomic is inherent to its chemical form, not dependent on its location.

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8. Directions : The following five (5) items consist of two statements, S

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.

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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.

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Both the statements are individually true and Statement II is the correct explanation of Statement I
Both the statements are individually true but Statement II is not the correct explanation of Statement I
Statement I is true but Statement II is false
Statement I is false but Statement II is true
This question was previously asked in
UPSC CDS-2 – 2017
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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.
While some UV-A radiation does pass through the atmosphere to the surface, and small amounts of UV-B can penetrate depending on ozone depletion, the primary role of the stratospheric ozone layer is protection against the most damaging forms of UV.

9. Consider the following statements about Chlorofluorocarbons (CFCs) :

Consider the following statements about Chlorofluorocarbons (CFCs) :

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  • 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 ?

1
2
3
None
This question was previously asked in
UPSC Geoscientist – 2024
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Correct Answer: C
– 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.
The discovery of the ozone-depleting potential of CFCs led to international agreements like the Montreal Protocol, which phased out the production and consumption of these substances. This has resulted in a gradual recovery of the ozone layer.

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10. The ultraviolet solar radiations are largely absorbed by

The ultraviolet solar radiations are largely absorbed by

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carbon dioxide and nitrogen
oxygen and carbon dioxide
oxygen and ozone
nitrogen and ozone
This question was previously asked in
UPSC Geoscientist – 2022
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Ultraviolet (UV) solar radiation is primarily absorbed by ozone (O3) in the stratosphere, which forms the ozone layer. Oxygen (O2) also absorbs some high-energy UV radiation (UV-C), contributing to the formation of 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).
Nitrogen and carbon dioxide are relatively transparent to ultraviolet radiation. Greenhouse gases like CO2 and water vapour are primarily involved in absorbing outgoing infrared radiation from the Earth’s surface, not incoming UV radiation.

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