Discuss in detail the photochemical smog emphasizing its formation, effects and mitigation. Explain the 1999 Gothenburg Protocol.
Approach · directive: “discuss / explain”
What it asks · Explain how photochemical smog forms, what harm it causes and how to curb it, and state what the 1999 Gothenburg Protocol requires.
The question has 2 parts — answer each
- Discuss photochemical smog in detail: its formation, its effects and its mitigation
- Explain the 1999 Gothenburg Protocol: what it is and what it requires
Open with · Photochemical smog is a brown haze of ground-level ozone and other oxidants formed when sunlight acts on vehicle and industrial emissions.
Cover
- Formation: nitrogen oxides and volatile organic compounds react in strong sunlight to make ozone, peroxyacetyl nitrate (PAN) and aldehydes; stagnant air and temperature inversion trap the haze.
- Health effects: eye irritation, cough, asthma and lung damage, worst for children and the elderly.
- Other effects: damage to crops and forests, cracked rubber and faded materials, poor visibility, and ozone adds to warming as a greenhouse gas.
- Mitigation: cleaner fuels and tighter vehicle norms, catalytic converters, public transport and electric vehicles, controls on solvents and petrol vapour, and smog alerts.
- Gothenburg Protocol, 1999: a UNECE protocol under the Convention on Long-range Transboundary Air Pollution that sets national emission ceilings for sulphur dioxide, nitrogen oxides, VOCs and ammonia to cut acidification, eutrophication and ground-level ozone.
- It was the first multi-pollutant, multi-effect protocol; the amended version, in force since 2019, adds 2020 targets and fine particles (PM2.5).
Close with · Coordinated control of the precursors, nitrogen oxides and VOCs, through clean transport and industry norms is the surest cure for photochemical smog.
Question: UPSC's CS (Main) 2022, GS Paper III — paper ↗. Approach: Minimalist IAS, checked 30 Sept 2026 (how we verify) — UPSC publishes no model answers. ·
Model answer · 223 words (UPSC limit 150) · Minimalist IAS
Photochemical smog is the brown haze of ground-level ozone and other oxidants that forms when strong sunlight acts on vehicle and industrial exhaust.
Formation
- Precursors: nitrogen oxides and volatile organic compounds (VOCs) from vehicle exhaust, refineries, solvents and petrol vapour.
- Reaction: in strong sunlight they react to form ozone, peroxyacetyl nitrate (PAN) and aldehydes; stagnant air and temperature inversion trap the haze over the city.
Effects
- Health: eye irritation, cough, asthma and lung damage, worst for children and the elderly.
- Environment and economy: damaged crops and forests, cracked rubber and faded materials, poor visibility, and ozone adds to warming as a greenhouse gas.
Mitigation
- Cut precursors: cleaner fuels and tighter vehicle norms, catalytic converters, controls on industrial solvents and petrol vapour recovery.
- Shift mobility: public transport and electric vehicles, with smog alerts to curb traffic on bad days.
Gothenburg Protocol, 1999
- Adopted under the UNECE Convention on Long-range Transboundary Air Pollution, it sets national emission ceilings for sulphur dioxide, nitrogen oxides, VOCs and ammonia to cut acidification, eutrophication and ground-level ozone together.
- It was the first multi-pollutant, multi-effect protocol; the amended version, in force since 2019, adds 2020 targets and fine particles (PM2.5).
Smog is made in the air from precursors, so coordinated control of nitrogen oxides and VOCs through clean transport and industry norms, the logic of Gothenburg, is the surest cure.
Written by Minimalist IAS from facts checked at source (how we verify) — a little fuller than exam length, so every part of the question is covered; in the hall, keep the structure and trim the detail. UPSC publishes no model answers: compare your structure and coverage with this, then write your own.