UPSC Mains 2022 GS Paper 3 Q7: model answer
Discuss in detail photochemical smog emphasizing its formation, effects, and mitigation. Explain the 1999 Gothenburg Protocol.
What the question wants
Explain the formation, effects and mitigation of photochemical smog, and the 1999 Gothenburg Protocol.
How to structure it
Formation, effects, mitigation, protocol.
- Formation
- Effects
- Mitigation
- Gothenburg Protocol
How to think it through
NOx + VOCs + sunlight → ozone, PAN, aldehydes; warm sunny, stagnant days; Los Angeles 1940s. Effects: respiratory, eye irritation, crop damage, materials, visibility. Mitigation: catalytic converters, BS-VI, public transport, VOC control at fuel stations (vapour recovery), industrial controls, EVs. Gothenburg Protocol 1999 under UNECE CLRTAP: to abate acidification, eutrophication and ground-level ozone; emission ceilings for SO2, NOx, VOCs, NH3; amended 2012 to add PM2.5 and black carbon; India not a party.
Model answer
Photochemical smog is the brown haze that hung over Los Angeles in the 1940s and now forms over Delhi, Beijing and Mexico City on hot, sunny days. Unlike London's coal smoke, it is cooked by sunlight.
Formation
- Nitrogen oxides from vehicles and power plants, and volatile organic compounds from fuels, paints and solvents, are released.
- Sunlight triggers reactions that form ground-level ozone, peroxyacetyl nitrate (PAN) and aldehydes.
- Worst on warm, sunny, still days with temperature inversions.
Effects
- Health: breathing problems, asthma attacks, eye irritation.
- Crops: ozone lowers wheat and rice yields.
- Materials: rubber and paints crack.
- Poor visibility.
Mitigation
- Catalytic converters and Bharat Stage VI norms.
- Vapour recovery at fuel stations; low-VOC paints.
- Public transport and electric vehicles.
- Industrial NOx controls.
The Gothenburg Protocol (1999)
- Under the UNECE Convention on Long- Range Transboundary Air Pollution.
- Aims to cut acidification, eutrophication and ground-level ozone.
- Sets national emission ceilings for SO2, NOx, VOCs and ammonia; amended in 2012 to add PM2.5.
Smog is made by cars and sunlight together, so it must be cut at the exhaust pipe.
Draw: A flow: NOx + VOCs + sunlight → ozone + PAN.
Keywords, cases and data to drop in
photochemical smog, NOx, VOCs, ozone, PAN, temperature inversion, Los Angeles, BS-VI, catalytic converter, vapour recovery, Gothenburg Protocol 1999, CLRTAP, emission ceilings, 2012 amendment.
Where most answers lose marks
- Confusing photochemical smog with sulphurous London smog.
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Question text as printed in the official UPSC Civil Services (Main) question paper. The model answer is original Battle IAS work; use it to learn structure, not to memorise.
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