Ozone Layer Depletion and Air Pollution: Complete Environment Notes for UPSC

Quick Answer: Ozone layer depletion and air pollution are two distinct atmospheric problems. Ozone depletion is the loss of stratospheric “good ozone” (15–35 km), caused mainly by CFCs and other ozone-depleting substances, leading to the Antarctic ozone hole. Air pollution is a tropospheric problem involving PM2.5, NO₂, SO₂ and ground-level “bad ozone”, tracked in India through the National AQI. The Montreal Protocol (1987) fixed the first; the second remains an ongoing challenge.

What Is the Ozone Layer and Where Is It Found?

The ozone layer sits in the stratosphere, roughly 15–35 km above the Earth’s surface, with peak concentration around 20–25 km. It contains a relatively high proportion of ozone (O₃) — still only a few molecules per million, but enough to absorb most of the Sun’s harmful ultraviolet-B (UV-B) radiation.

In exam terminology this is “good ozone”: it shields life on Earth from skin-damaging UV rays. The ozone layer was discovered by French physicists Henri Buisson and Charles Fabry in 1913. Refer to NASA’s ozone resource for authoritative detail: NASA Ozone Watch.

How CFCs and ODS Deplete Stratospheric Ozone

Chlorofluorocarbons (CFCs), along with halons, carbon tetrachloride and HCFCs, are ozone-depleting substances (ODS). Being extremely stable, CFCs survive long enough to drift up to the stratosphere, where intense UV radiation breaks them apart — a process called photolysis — releasing chlorine radicals.

The chlorine radical then reacts catalytically:

• Cl + O₃ → ClO + O₂
• ClO + O → Cl + O₂

The chlorine atom is regenerated, so one chlorine atom can destroy up to ~100,000 ozone molecules before it is locked away in reservoir compounds — a favourite one-liner in SSC and Banking papers.

Why the hole is over Antarctica: Polar stratospheric clouds form in Antarctica’s extreme winter cold (below −78°C). On the surfaces of these ice clouds, reservoir compounds release active chlorine when sunlight returns in spring (September–October). The 1985 discovery of the ozone hole by the British Antarctic Survey (Joe Farman) triggered global action.

What Is Tropospheric (Ground-Level) Air Pollution?

Air pollution occurs in the troposphere — the lowest layer of the atmosphere, extending about 8–15 km up. Here, ozone is “bad ozone”: a secondary pollutant formed when NOₓ and volatile organic compounds (VOCs) react in sunlight. Vehicle exhaust, industrial emissions, stubble burning and thermal power plants are the chief sources.

Sunlight-driven NOₓ + VOC chemistry also produces photochemical smog — the haze that chokes Delhi every winter (mixed with thermal inversion effects). Unlike ozone depletion, air pollution is largely local to regional in origin but global in cumulative impact.

Major Air Pollutants and National AQI Basics

India launched the National Air Quality Index (AQI) in 2014 under the Swachh Bharat campaign, spearheaded by the CPCB. It measures eight pollutants:

• PM2.5 (fine particulate matter, ≤2.5 microns — most harmful)
• PM10 (coarse particulate matter)
• NO₂ (nitrogen dioxide)
• SO₂ (sulphur dioxide)
• CO (carbon monoxide)
• O₃ (ground-level ozone)
• NH₃ (ammonia)
• Pb (lead)

The AQI has six colour-coded categories: Good (0–50), Satisfactory (51–100), Moderately Polluted (101–200), Poor (201–300), Very Poor (301–400) and Severe (401–500). Official details: CPCB and real-time data at CPCB AQI portal.

Comparison Table: Ozone Depletion vs Air Pollution

Health and Environmental Effects of Both Phenomena

Ozone depletion → more UV-B reaching Earth:

• Skin cancers including melanoma
• Cataracts and eye damage
• Suppression of the immune system
• Damage to phytoplankton and crop yields

Air pollution effects: chronic obstructive pulmonary disease (COPD), asthma, lung cancer, heart attacks and strokes from PM2.5; acid rain from SO₂ and NOₓ; crop damage and reduced agricultural productivity. The WHO attributes roughly 7 million premature deaths annually to air pollution (WHO – Air Pollution).

Montreal Protocol 1987: Milestones and Amendments

The Montreal Protocol on Substances that Deplete the Ozone Layer was adopted on 16 September 1987 (now International Day for the Preservation of the Ozone Layer) and entered into force in 1989, under the Vienna Convention (1985) framework. It is the first treaty to achieve universal ratification — all 198 UN members — earning its title as the most successful environmental treaty ever.

Key amendments:

• London (1990): added controls, created the Multilateral Fund
• Copenhagen (1992): accelerated CFC phase-out to 1996 for developed countries
• Montreal (1997) and Beijing (1999): tightened controls on HCFCs and brominated substances, trade licensing
• Kigali (2016): HFC phase-down

Official source: UNEP Ozone Secretariat.

Kigali Amendment 2016 and HFC Phase-Down

Hydrofluorocarbons (HFCs) replaced CFCs because they do not deplete ozone — but they are potent greenhouse gases (some with global warming potential thousands of times that of CO₂). The Kigali Amendment, adopted in Rwanda in October 2016 and in force from 1 January 2019, phases down HFC production and consumption under the same Protocol. India ratified it in 2021. It is expected to avoid up to ~0.4°C of global warming by 2100 — a classic UPSC prelims fact. Details: US EPA on HFCs.

India’s Actions: CFC Phase-Out, HCFC Stage-Out and SAFAR

• India phased out CFC production and consumption fully by 2010 (ahead of the Montreal schedule).
• India is phasing out HCFCs under the HCFC Phase-out Management Plan (HPMP); the Ozone Depleting Substances (Regulation and Control) Rules, 2000 govern production and trade.
• SAFAR (System of Air Quality and Weather Forecasting and Research), developed by IITM, Pune under the Ministry of Earth Sciences, provides city-level air quality forecasts (Delhi, Pune, Mumbai, Ahmedabad).
• The National Clean Air Programme (NCAP, 2019) targets reductions in PM concentrations in non-attainment cities.

Previous Year Questions (PYQ) Patterns: UPSC, SSC and Banking

• UPSC Prelims: match-the-following on ozone chemistry, Vienna Convention/Montreal Protocol/Kigali facts, “good vs bad ozone” distinctions.
• SSC CGL/CHSL: one-liners — year of Montreal Protocol (1987), chlorine radical’s ~100,000 ozone destruction, AQI launch year (2014), International Ozone Day (16 September).
• Banking/RBI: environment questions in GA sections — Kigali Amendment, India’s ratification year (2021).
• UPSC Mains: GS-III essays on treaty effectiveness (“Montreal success vs climate impasse”) and urban air quality governance.

Revision Pointers and Memory Tricks

• AQI pollutants mnemonic — “PM N SOC ONP”: PM2.5, PM10, NO₂, SO₂, CO, O₃, NH₃, Pb. Or remember “3 particulate-free pairs“: NO₂–SO₂, CO–O₃, NH₃–Pb, plus the two PMs.
• Protocol dates chain: Vienna 85 → Montreal 87 → London 90 → Copenhagen 92 → Beijing 99 → Kigali 16.
• Good vs bad ozone: “Up is good, down is bad” — stratospheric ozone protects; tropospheric ozone pollutes.
• AQI categories: “G-S-M-P-V-S” — Good, Satisfactory, Moderate, Poor, Very Poor, Severe (6 categories).

Conclusion and Exam Takeaways

The Montreal Protocol shows that a binding, universally ratified treaty with clear phase-out schedules and finance (Multilateral Fund) can actually repair a global environmental problem — the ozone layer is on track to recover to 1980 levels by around 2066 over Antarctica. Air pollution, by contrast, remains a decentralised, largely domestic challenge requiring city-level action (NCAP, SAFAR, AQI monitoring). For exams, keep the two cleanly separated: stratosphere + CFCs + Montreal/Kigali versus troposphere + PM2.5/NOₓ/VOCs + AQI/NCAP. Master this distinction and most questions in this section become free marks.

Frequently Asked Questions

Q: Is ozone depletion the same as air pollution?

No. Ozone depletion is the loss of stratospheric “good ozone” caused by CFCs and other ODS; air pollution is a tropospheric problem that includes “bad ozone” formed from NOₓ and VOCs in sunlight.

Q: When did the Montreal Protocol come into force and when was the Kigali Amendment adopted?

The Montreal Protocol was signed in 1987 and entered into force in 1989; the Kigali Amendment was adopted in 2016, entered into force in 2019, and India ratified it in 2021.

Q: Which pollutants are measured in India’s AQI?

Eight pollutants: PM2.5, PM10, NO₂, SO₂, CO, O₃, NH₃ and lead. The AQI has six colour-coded categories, from Good (0–50) to Severe (401–500).

Q: Why did the Kigali Amendment target HFCs if they don’t deplete ozone?

HFCs replaced CFCs but are potent greenhouse gases. Kigali phases them down under the Montreal Protocol’s institutional machinery to fight climate change, potentially avoiding ~0.4°C of warming by 2100.

Q: What does one chlorine atom from a CFC molecule do?

UV radiation splits CFCs in the stratosphere, releasing chlorine radicals. A single chlorine atom can catalytically destroy up to ~100,000 ozone molecules before being deactivated.

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