UPSC CSE Prelims
Greenhouse Gases Previous Year Questions (PYQs)

Detailed Explanation:

Statement I — Incorrect. India's per capita CO₂ emissions are around 1.9–2.0 tonnes, NOT less than 0.5 tonnes. The number given is too low and wrong.

Statement II — Correct. India ranks second in the Asia-Pacific region for CO₂ emissions from fuel combustion — after China (which ranks first).

Statement III — Correct. Electricity and heat production (mostly coal-based) is the largest source of CO₂ emissions in India.

Detailed Explanation:

Answer: Option 3 — Only three

Hydrofluorocarbons (HFCs) are synthetic compounds primarily used as replacements for ozone-depleting substances. Among the given applications, HFCs are used in aerosols (as propellants), foam agents (for blowing plastic foams), and fire retardants (as clean fire suppressants), but NOT in lubricants.

✅ Aerosols – Correct: HFCs serve as non-flammable propellants in aerosol products like hairsprays, deodorants, and cleaning sprays.
✅ Foam agents – Correct: HFCs are widely used as foam-blowing agents in manufacturing polyurethane and polystyrene foams for thermal insulation.
✅ Fire retardants – Correct: HFCs (such as HFC-227ea) are used as "clean agents" in fire suppression systems, replacing ozone-depleting Halons.
❌ Lubricants – Incorrect: Lubricants are formulated from mineral oils, synthetic hydrocarbons (polyalphaolefins), or esters, not HFCs.

📝 Short Notes: Hydrofluorocarbons (HFCs)

• Nature: Synthetic organic compounds containing hydrogen, fluorine, and carbon atoms; do not contain chlorine.
• Ozone Impact: HFCs do not deplete the ozone layer (unlike CFCs and HCFCs) as they lack chlorine and bromine.
• Climate Impact: Potent greenhouse gases with high Global Warming Potential (GWP), ranging from hundreds to thousands of times that of CO₂.
• Common Uses: Refrigeration and air conditioning, aerosol propellants, foam-blowing agents, fire suppression systems, and solvent applications.
• Regulatory Framework: Controlled under the Kigali Amendment (2016) to the Montreal Protocol, which mandates phased reduction of HFC production and consumption.
• India's Commitment: India ratified the Kigali Amendment in 2021, committing to reduce HFC use by 85% by 2047.
• Alternatives: Natural refrigerants (ammonia, CO₂, hydrocarbons), HFOs (hydrofluoroolefins) with lower GWP.

Detailed Explanation:

Answer: Option 2 — Rice

Rice cultivation is the most important anthropogenic source of both methane (CH₄) and nitrous oxide (N₂O) among the given crops. Flooded rice paddies create anaerobic conditions that promote methane production by methanogenic bacteria, which is then released through the rice plants. Additionally, the heavy use of nitrogen-based fertilizers in rice cultivation leads to nitrous oxide emissions when soil microbes convert excess nitrogen that is poorly absorbed by the rice plants.

📝 Short Notes: Greenhouse Gas Emissions from Agriculture

• Methane from Rice: Waterlogged paddy fields create oxygen-depleted (anaerobic) conditions ideal for methanogenic archaea, producing CH₄ that escapes through rice plant stems and soil.
• Nitrous Oxide from Fertilizers: Nitrogen fertilizers undergo microbial processes (nitrification and denitrification) in soil, releasing N₂O, especially when applied in excess.
• Global Warming Potential: CH₄ is 28-34 times more potent than CO₂ over 100 years; N₂O is approximately 265-298 times more potent than CO₂.
• Rice vs Other Crops: Cotton, wheat, and sugarcane are primarily upland crops without prolonged flooding, producing minimal methane. Rice paddies account for ~10-12% of global methane emissions.
• Mitigation Strategies: Alternate wetting and drying (AWD), improved fertilizer management, use of slow-release fertilizers, and development of low-emission rice varieties.

Detailed Explanation:

Answer: Option 4 — 1, 2 and 3

All three statements are correct as agricultural soils, cattle, and poultry industry are significant sources of reactive nitrogen compounds that contribute to environmental pollution and climate change.

✅ Statement 1 – Correct: Agricultural soils release nitrogen oxides (particularly nitrous oxide - N₂O) through microbial processes like nitrification and denitrification, especially from nitrogen-based fertilizers.

✅ Statement 2 – Correct: Cattle release ammonia (NH₃) into the environment primarily through urine and manure decomposition, contributing to air pollution and acid rain.

✅ Statement 3 – Correct: The poultry industry releases reactive nitrogen compounds including ammonia, nitrous oxide, and nitrogen oxides from manure management and feed production processes.

📝 Short Notes: Reactive Nitrogen Pollution

• Nitrogen Oxides (NOx): Primarily N₂O from agricultural soils; potent greenhouse gas with ~300 times the warming potential of CO₂; also contributes to ozone depletion.
• Ammonia (NH₃): Released from livestock waste and manure; forms particulate matter (PM2.5) in atmosphere; contributes to eutrophication when deposited in water bodies.
• Sources of Agricultural Nitrogen: Synthetic fertilizer application, animal manure, crop residue decomposition, and legume cultivation.
• Environmental Impacts: Air quality degradation, soil acidification, water pollution, biodiversity loss, and greenhouse gas emissions.
• Livestock Contribution: Global livestock sector responsible for ~10-12% of anthropogenic greenhouse gas emissions, with significant nitrogen compounds release.