Ozone Layer Depletion Montreal Protocol

Ozone Layer Depletion and Montreal Protocol (UPSC Prelims + Mains Notes)

Think of a very hot Indian summer day. You carry an umbrella, wear sunglasses, and apply sunscreen. But even with all this, your skin can burn if the Sun's ultraviolet (UV) rays are too strong. The ozone layer is Earth's natural "UV filter". When it gets thinner, more harmful UV reaches us.

The Ozone Paradox: Distinguishing between 'Good' stratospheric ozone that protects from UV radiation and 'Bad' ground-level ozone as a potent pollutant.

This topic is important for UPSC because it connects environment, science, international treaties, climate policy, and India's regulatory action. The Montreal Protocol is also one of the most successful global environmental treaties, often used as a model for cooperation.

Quick Overview for UPSC

What is the ozone layer? A region in the stratosphere with high ozone (O₃) that absorbs harmful UV radiation.
What is ozone depletion? Long-term thinning of the stratospheric ozone due to chemicals like CFCs releasing chlorine/bromine in the stratosphere.
What is the ozone hole? A seasonal extreme depletion mainly over Antarctica during Southern Hemisphere spring.
Core treaty: Montreal Protocol (1987), enforced from 1989, controls ozone-depleting substances (ODS).
Related treaty: Vienna Convention (1985) is the framework; Montreal Protocol gives binding controls.
New climate link: Kigali Amendment (2016) targets HFCs (not ODS, but strong greenhouse gases).
India: Ozone Cell (MoEFCC), ODS Rules, 2000, phase-out plans, and transition to ozone-friendly technologies.

1) Ozone Layer: Meaning, Location, and Role

📘 Ozone Layer

A region in the Earth's stratosphere (roughly 15–35 km altitude) where ozone (O₃) concentration is high enough to absorb most harmful UV-B and almost all UV-C radiation.

UV-B Biological Impact: The damaging effects of ultraviolet radiation on cellular structures and ecosystems, emphasizing the need for ozone layer protection.

📘 Stratosphere

The atmospheric layer above the troposphere, extending roughly from about 10 km to 50 km. It contains the ozone layer and is more stable (less vertical mixing) than the troposphere.

Why ozone is crucial: Ozone absorbs dangerous UV radiation. Without it:

Skin cancers and cataracts would increase sharply.
Immune suppression risks would rise.
Crops and forests could lose productivity.
Marine food chains (phytoplankton) could get disrupted.

Types of UV radiation (UPSC-friendly)

UV-C: Most harmful; almost fully blocked by ozone and oxygen.
UV-B: Harmful; partially blocked by ozone. Main concern in ozone depletion.
UV-A: Least energetic; mostly reaches Earth and contributes to tanning/skin ageing.

2) How Ozone is Formed and Destroyed Naturally (Chapman Cycle)

📘 Chapman Cycle

The natural set of reactions that create and destroy ozone in the stratosphere using sunlight and oxygen molecules/atoms, maintaining a dynamic balance.

Simple explanation: Sunlight breaks oxygen (O₂) into oxygen atoms (O). These oxygen atoms combine with O₂ to form ozone (O₃). Ozone also breaks down naturally. So ozone is always being made and destroyed, but normally stays in balance.

Key idea for UPSC: Ozone depletion becomes serious when human-made chemicals speed up ozone destruction beyond the natural balance.

3) Ozone Depletion vs Ozone Hole

📘 Ozone Depletion

A long-term reduction in the total amount of stratospheric ozone, mainly caused by ozone-depleting substances (ODS) releasing chlorine and bromine radicals that destroy ozone.

📘 Ozone Hole

A region of severe seasonal ozone depletion (mainly over Antarctica) where total ozone drops dramatically during spring. It is called a "hole" but ozone is not completely absent.

Important UPSC point: The ozone hole is strongest over Antarctica because of special conditions:

Very low temperatures in polar winter
Formation of polar stratospheric clouds (PSCs)
Strong polar vortex trapping air
Return of sunlight in spring triggers rapid ozone destruction

📘 Dobson Unit (DU)

A unit to measure total ozone in a column of air above a location. Typical global values are often around a few hundred DU. The Antarctic "ozone hole" is commonly associated with values below about 220 DU.

4) Main Cause: Ozone-Depleting Substances (ODS)

📘 Ozone-Depleting Substances (ODS)

Chemicals that release chlorine or bromine in the stratosphere and destroy ozone catalytically. Examples: CFCs, halons, carbon tetrachloride, methyl chloroform, HCFCs, methyl bromide.

Why were ODS widely used? Many ODS were stable, non-flammable, and effective for:

Refrigeration and air-conditioning (coolants)
Aerosol propellants (older sprays)
Foam blowing (insulation, packaging)
Fire extinguishers (halons)
Industrial cleaning solvents

Why do CFCs cause damage mainly in the stratosphere?

CFCs are very stable in the lower atmosphere. They remain for years and slowly travel upward. In the stratosphere, strong UV breaks them and releases chlorine radicals.

📘 Catalytic Ozone Destruction

A process where a reactive radical (like chlorine) destroys ozone repeatedly without being consumed, so one chlorine atom can destroy many ozone molecules.

Simple reaction idea:

Cl + O₃ → ClO + O₂
ClO + O → Cl + O₂
Net: O₃ + O → 2O₂

5) Why Antarctica is Special: Polar Stratospheric Clouds (PSCs)

📘 Polar Stratospheric Clouds (PSCs)

Clouds that form in the extremely cold polar stratosphere. They enable chemical reactions that convert chlorine into "active" forms that rapidly destroy ozone when sunlight returns in spring.

UPSC-ready explanation:

During polar winter, sunlight is absent and temperatures are extremely low.
PSCs form and provide surfaces for reactions that convert "safe" chlorine compounds into reactive chlorine.
When spring sunlight returns, the reactive chlorine destroys ozone very quickly.

6) Impacts of Ozone Depletion

A) Human health

Skin cancer: Increased UV-B increases risks.
Cataracts and eye damage: UV affects eye lens.
Immune suppression: Higher UV exposure can weaken immune responses.

B) Agriculture and forests

UV-B can reduce crop yields (damage to plant tissues and photosynthesis).
Sensitive crops and seedlings can be affected.

C) Marine ecosystems

UV can reduce phytoplankton productivity, affecting the marine food chain.
Fish larvae and amphibian eggs can be sensitive to UV.

D) Materials and economy

Faster degradation of plastics, rubber, paints, and building materials.
Higher healthcare costs and productivity loss.

7) The Global Response: Vienna Convention and Montreal Protocol

Chronology (must-remember for Prelims)

Year	Event	Why Important
1985	Vienna Convention for the Protection of the Ozone Layer	Framework for cooperation, research, monitoring
1987	Montreal Protocol on Substances that Deplete the Ozone Layer	Binding controls to phase out ODS
1989	Montreal Protocol enters into force	Implementation begins
1990	London Amendment	Stronger controls, more ODS added
1992	Copenhagen Amendment	Further strengthened phase-out schedules
1997	Montreal Amendment	Licensing systems for controlled substances
1999	Beijing Amendment	More chemicals controlled, tighter measures
2016	Kigali Amendment	Phase-down of HFCs (climate link)

8) Vienna Convention (1985): The Framework

📘 Vienna Convention (1985)

An international agreement to promote cooperation on research, systematic observation, information exchange, and adoption of measures to protect the ozone layer. It provided the legal and scientific foundation for the Montreal Protocol.

UPSC angle: Vienna Convention is a framework convention. It encouraged cooperation but did not set specific binding phase-out targets. Those came under the Montreal Protocol.

9) Montreal Protocol (1987): The Core Treaty

📘 Montreal Protocol (1987)

A legally binding global treaty to control and phase out production and consumption of ozone-depleting substances (ODS), with different timelines for developed and developing countries.

Why Montreal Protocol is called a "success story"

Universal participation: Almost every country joined.
Science-policy link: Regular assessments update policy.
Flexible mechanism: "Adjustments" can tighten controls without rewriting the whole treaty.
Financial + technology support: Help for developing countries through the Multilateral Fund.
Trade provisions: Controls trade in ODS with non-parties to encourage participation.

📘 Multilateral Fund (MLF)

A financial mechanism under the Montreal Protocol that supports developing countries (Article 5 parties) in phasing out ODS through funding, technology transfer, capacity building, and training.

📘 Article 5 Parties

Developing countries under the Montreal Protocol that receive grace period and financial/technical assistance to meet phase-out targets, based on lower per-capita ODS consumption thresholds.

10) What Substances are Controlled? (Very Important for Prelims)

Major ODS groups (easy list)

CFCs: Used in old refrigerators, ACs, aerosols, foam.
Halons: Fire-fighting (very high ozone damage due to bromine).
Carbon tetrachloride: Solvent and industrial uses.
Methyl chloroform: Industrial cleaning solvent.
HCFCs: Transitional substitutes for CFCs; still ozone-depleting (lower ODP), being phased out.
Methyl bromide: Fumigant (pesticide) used in agriculture; phased down with exemptions.

📘 Ozone Depletion Potential (ODP)

A relative measure of how much a substance can destroy ozone compared to CFC-11 (ODP = 1). Higher ODP means more ozone damage.

11) How Montreal Protocol Works (Mechanism and Institutions)

A) Control schedules

Countries must reduce and eventually eliminate the production and consumption of listed ODS as per agreed timelines. "Consumption" typically means production + imports − exports.

B) Differentiated responsibilities

Developing countries got more time and support because they had lower historical responsibility and needed time for technology transition.

C) Reporting and licensing

Countries report data on production and consumption.
Licensing systems help track and control imports/exports of controlled substances.

D) Scientific and technical assessment

Scientific panels review ozone science and recommend updates.
Technical bodies assess alternatives and cost-effective pathways.

E) Compliance mechanism (non-punitive, corrective)

The Protocol is known for a cooperative compliance approach, helping countries return to compliance rather than only punishing.

12) HCFCs: The Transitional Problem

📘 HCFC (Hydrochlorofluorocarbon)

A class of chemicals used as transitional substitutes for CFCs. They have lower ODP than CFCs but still deplete ozone, so they are being phased out under the Montreal Protocol.

Why HCFCs were used: They were easier "drop-in" replacements for CFC technology in refrigeration and foam. But because they still harm ozone, the world decided to phase them out.

UPSC trap: "HCFCs are ozone-friendly" is wrong. They are less harmful than CFCs but still ODS.

13) Kigali Amendment (2016): The Climate Link

📘 HFC (Hydrofluorocarbon)

Chemicals widely used as replacements for CFCs/HCFCs in refrigeration and air-conditioning. They have zero ODP (do not deplete ozone), but many have high global warming potential (GWP).

📘 Kigali Amendment (2016)

An amendment to the Montreal Protocol that aims to phase down HFCs globally because they are strong greenhouse gases, even though they do not deplete ozone.

📘 Global Warming Potential (GWP)

A measure of how much heat a greenhouse gas traps in the atmosphere compared to CO₂ over a specific time period (often 100 years). CO₂ has GWP = 1.

Why Kigali matters for India: India has huge cooling demand (homes, offices, cold chains, food storage). A low-GWP transition can protect climate while supporting development.

Very clear UPSC distinction

Montreal Protocol: Protects ozone (controls ODS like CFCs, HCFCs, halons).
Kigali Amendment: Protects climate (phases down HFCs).

14) India and Ozone Protection: Laws, Institutions, and Actions

A) Institutional setup

Ozone Cell under the Government of India coordinates Montreal Protocol implementation.
Works with industry, customs, and implementing agencies to meet targets.

B) Key legal step

📘 ODS (Regulation and Control) Rules, 2000

India's rules notified under the Environment (Protection) Act, 1986 to regulate and control manufacture, import, export, and use of ozone-depleting substances, supporting Montreal Protocol compliance.

C) What India practically did (UPSC-ready points)

Stopped or reduced use of major ODS in industry through phase-out plans.
Shifted to ozone-friendly alternatives in refrigeration, foam, aerosols, and solvents.
Training of refrigeration/AC servicing sector to prevent leaks and improve safety with new refrigerants.
Strengthened customs and licensing to reduce illegal trade of ODS.

D) Why this is challenging for India

Large informal servicing sector in refrigeration/AC.
Need for affordable cooling for development and public health.
Safety issues with some alternatives (flammability/toxicity) need training and standards.
Balancing ozone safety and climate safety together (low ODP + low GWP).

15) Ozone Protection and Climate Change: Relationship (Common UPSC Confusion)

A) Ozone depletion is NOT the main cause of global warming

Ozone depletion and global warming are different problems. But they are linked because many ODS are also strong greenhouse gases.

B) Montreal Protocol also helped climate indirectly

Many ODS (like CFCs) trap heat strongly.
Phasing them out reduced warming pressures.
But some substitutes (HFCs) created a new climate challenge, which Kigali addresses.

C) Simple one-line UPSC memory

Montreal saved ozone first, and also helped climate; Kigali is to ensure the replacements do not heat the planet.

16) Current Status: Is the Ozone Layer Recovering?

Because countries reduced ODS under the Montreal Protocol, the amount of ozone-destroying chlorine and bromine in the stratosphere has been declining over time. This supports recovery of the ozone layer. However, recovery is slow because many ODS stay in the atmosphere for long durations.

UPSC takeaway: The ozone layer is on a recovery path due to global action, but strict compliance, stopping illegal ODS trade, and managing substitutes (HFCs) remain important.

17) Role of Technology and Alternatives (Prelims + Mains)

Better alternatives used today

HFOs (hydrofluoroolefins): often lower GWP than HFCs.
Natural refrigerants: ammonia (NH₃), carbon dioxide (CO₂), hydrocarbons (propane/isobutane) — require safety standards and skilled handling.
Energy efficiency improvements: Efficient cooling reduces both emissions and electricity demand.

Why efficiency is a big UPSC angle

India's future electricity demand will rise due to cooling needs.
Efficient cooling reduces load, improves energy security, and reduces emissions.
Policies can combine Kigali goals with energy efficiency standards.

18) UPSC Prelims: High-Probability Statements (Concept Checks)

Montreal Protocol is related to ozone protection, not directly to CO₂ reduction.
CFCs and halons are ODS with high ozone damage.
HCFCs are transitional ODS with lower ODP than CFCs but still harmful.
HFCs do not deplete ozone (ODP ~ 0) but many have high GWP.
Kigali targets HFC phase-down under the Montreal framework.
Ozone hole is strongest over Antarctica due to PSCs and polar vortex.
Ozone is measured in Dobson Units.

19) UPSC Mains: Answer Writing Points

A) Introduction ideas (choose one)

Define ozone layer and its protective role against UV radiation.
Start with the "global commons" idea and the success of Montreal Protocol.
Use a data-style line: ODS reduction led to ozone recovery trend (without needing exact numbers).

B) Body structure (best format)

Causes: CFCs, halons, HCFCs; catalytic destruction; PSCs in polar regions.
Impacts: Health, agriculture, marine ecosystems, materials.
Global response: Vienna + Montreal + amendments; MLF; compliance mechanism.
India's response: ODS Rules 2000, Ozone Cell, phase-out plans, challenges in cooling sector.
Way forward: low-GWP transition, energy-efficient cooling, skill training, enforcement against illegal trade.

C) Conclusion lines (ready to use)

Montreal Protocol proves that science-based cooperation can solve global environmental crises.
India can lead in climate-friendly cooling by combining Kigali goals with energy efficiency and strong standards.

20) PYQ Boxes (Theme-Based for UPSC)

📝 UPSC PYQ (Theme) - Montreal Protocol

Questions commonly test: Which treaty targets ozone depletion? Which chemicals are controlled (CFCs/HCFCs/halons)? What is the objective of the Montreal Protocol?

📝 UPSC PYQ (Theme) - Ozone Hole vs Ozone Depletion

Questions commonly test: Why is ozone hole prominent over Antarctica? Role of polar stratospheric clouds and sunlight in spring.

The Montreal Protocol: A historic timeline of the most successful global environmental agreement, from its 1987 signing to the 2016 Kigali Amendment.

📝 UPSC PYQ (Theme) - HFCs and Kigali Amendment

Questions commonly test: HFCs do not deplete ozone but contribute to global warming; Kigali amendment phases down HFCs under Montreal framework.

📝 UPSC PYQ (Theme) - Dobson Unit and UV Radiation

Questions commonly test: Meaning of Dobson Unit; which UV type is most blocked by ozone; which UV type increases health risks when ozone depletes.

📝 UPSC PYQ (Theme) - International Environmental Governance

Questions commonly test: Why Montreal is successful (universal participation, financial mechanism, binding controls, scientific assessment panels).

21) Practice MCQs (UPSC Prelims Style) with Answers and Explanations

MCQ 1

Which of the following best describes the role of the ozone layer?

A) Absorbing infrared radiation to control global warming
B) Absorbing UV-B and UV-C radiation to protect life
C) Producing oxygen through photosynthesis
D) Preventing earthquakes by stabilizing the atmosphere

Answer: B

Explanation: The ozone layer mainly absorbs harmful ultraviolet radiation (especially UV-B and UV-C), protecting humans and ecosystems.

MCQ 2

The "ozone hole" is most strongly observed over Antarctica mainly because:

A) High industrial pollution over Antarctica
B) Presence of polar stratospheric clouds and strong polar vortex
C) High temperatures in the stratosphere
D) High ocean salinity around Antarctica

Answer: B

Explanation: Extremely cold polar stratosphere forms PSCs and a polar vortex, enabling rapid ozone destruction when sunlight returns.

MCQ 3

Consider the following statements:

1) CFCs are stable in the lower atmosphere and release chlorine radicals mainly in the stratosphere.
2) Chlorine radicals destroy ozone through catalytic reactions.

Which is correct?

A) 1 only
B) 2 only
C) Both 1 and 2
D) Neither 1 nor 2

Answer: C

Explanation: Both statements are correct and form the core scientific explanation of ozone depletion.

MCQ 4

Montreal Protocol (1987) primarily targets the reduction of:

A) CO₂
B) Methane
C) Ozone-depleting substances like CFCs and halons
D) Nitrogen gas

Answer: C

Explanation: Montreal Protocol controls ODS (CFCs, halons, HCFCs, etc.) to protect the ozone layer.

MCQ 5

Which of the following is correct about HFCs?

A) They have high ODP and low GWP
B) They have zero ODP but many have high GWP
C) They are natural gases produced by oceans
D) They are the main cause of the Antarctic ozone hole

Answer: B

Explanation: HFCs do not deplete ozone, but many are strong greenhouse gases, so Kigali targets them.

MCQ 6

Which treaty is the framework convention that led to the Montreal Protocol?

A) Basel Convention
B) Vienna Convention (1985)
C) Ramsar Convention
D) Cartagena Protocol

Answer: B

Explanation: Vienna Convention provided cooperation and research framework; Montreal Protocol introduced binding controls.

MCQ 7

Dobson Unit (DU) is used to measure:

A) Ocean depth
B) Total ozone in an atmospheric column
C) Earthquake magnitude
D) Soil fertility

Answer: B

Explanation: DU measures total ozone overhead in a column of air.

MCQ 8

Which of the following are controlled substances under the Montreal Protocol (originally or via later amendments)?

1) CFCs
2) Halons
3) HCFCs
4) CO₂

Select the correct answer:

A) 1 and 2 only
B) 1, 2 and 3 only
C) 2 and 4 only
D) 1, 2, 3 and 4

Answer: B

Explanation: CFCs, halons, and HCFCs are ODS. CO₂ is not an ODS.

MCQ 9

The Kigali Amendment is significant because it:

A) bans all plastic production worldwide
B) phases down HFCs to reduce global warming impacts
C) bans nuclear energy
D) creates a global forest police force

Answer: B

Explanation: Kigali targets HFC phase-down due to high GWP.

MCQ 10

India's key domestic step to regulate ODS includes:

A) ODS (Regulation and Control) Rules, 2000
B) Forest Rights Act, 2006
C) Biological Diversity Act, 2002
D) Disaster Management Act, 2005

Answer: A

Explanation: India notified ODS Rules in 2000 to support Montreal Protocol compliance.

22) One-Page Revision (Last-Minute Prelims Notes)

Ozone layer: Stratosphere; absorbs UV-B/UV-C.
Ozone depletion: Long-term thinning due to ODS.
Ozone hole: Seasonal extreme depletion over Antarctica (PSCs + polar vortex + spring sunlight).
Key ODS: CFCs, halons, HCFCs, methyl bromide, etc.
Vienna (1985): Framework; research and cooperation.
Montreal (1987): Binding controls; phase-out; Multilateral Fund.
Kigali (2016): HFC phase-down (climate link).
India: Ozone Cell + ODS Rules (2000) + enforcement + transition to alternatives.

23) Mini Mains Practice (Optional)

Q1. Explain the causes of ozone depletion and evaluate the role of the Montreal Protocol in addressing it. Also discuss India's efforts and the new challenges due to HFCs.

Hints: Start with ozone role; chemistry (chlorine/bromine catalytic cycles); Antarctic PSCs; Montreal features (phase-out, MLF, compliance, trade controls); India rules and sectoral transition; Kigali and climate-friendly cooling.