Ozone depletion, Montreal Protocol & Kigali Amendment

Ozone questions become easy only when the student separates layer, substance and treaty before reading the options.

• Core definition: Ozone depletion means a long-term thinning of stratospheric ozone, especially the seasonal Antarctic ozone hole, caused mainly by human-made ozone-depleting substances. It is not the same as ground-level ozone pollution, which is a harmful secondary pollutant in the lower atmosphere.
• Layer distinction: Beneficial ozone is concentrated in the stratosphere and screens biologically damaging ultraviolet radiation; surface ozone belongs to air-pollution chemistry and appears with nitrogen oxides, volatile organic compounds and sunlight. UPSC frequently turns this vertical location difference into a statement trap.
• Syllabus placement: The topic sits at the junction of environmental ecology, climate change and international environmental governance. It requires no specialised chemistry, but it does require knowing mechanisms, treaties, Indian legal tools, phase-out schedules and the climate link of refrigerants.
• Public-health link: More ultraviolet-B exposure is associated with skin cancer risk, cataracts, crop damage, marine plankton stress and material degradation. These consequences explain why the ozone regime was framed as a global environmental-health response rather than a narrow industrial regulation.
• Climate link without confusion: Many controlled ozone-depleting substances are also greenhouse gases. HFCs, however, generally do not deplete ozone; they entered the Montreal Protocol system through the Kigali Amendment because they are powerful greenhouse gases used as replacements in cooling.
• India angle: India studies this topic through constitutional environment duties, the Environment Protection Act, 1986, Ozone Depleting Substances Rules, 2000, Ozone Cell implementation, HCFC phase-out and the HFC phase-down pathway after Kigali ratification in September 2021.
• Exam boundary: Do not over-read the topic as a complete climate-convention chapter. UNFCCC, Kyoto and Paris belong to climate governance, while Vienna, Montreal and Kigali form the ozone-refrigerant regime with strong climate co-benefits.
• Weight in Prelims: Questions usually test exact treaty years, whether HFCs are ozone-depleting, the meaning of Article 5 parties, controlled substances, India's phase-down schedule, and the difference between production-consumption controls and emission-only promises.
• Dobson-unit awareness: Ozone amount is commonly expressed as Dobson Units, a column measure rather than a surface concentration. A sharp Prelims question may mix Dobson Units with Air Quality Index units; the former belongs to total-column ozone, while the latter belongs to local air-pollution reporting.