Consider the following:
- 1.Carbon monoxide
- 2.Methane
- 3.Ozone
- 4.Sulphur dioxide
Which of the above are released into atmosphere due to the burning of crop/biomass residue?
Answer & explanation
Answer: (d) 1, 2, 3 and 4
Why not the tempting option · UPSC's key counts ozone among the gases released due to crop-residue burning. Ozone is a secondary pollutant that forms in the air from the nitrogen oxides and volatile organic compounds in the smoke, but the question says 'due to the burning', which covers that. The doubt does not change the answer: carbon monoxide, methane and sulphur dioxide are certainly emitted, and (d) is the only option that contains all three. In the exam, settle the sure statements first and let the option grid decide the rest.
UPSC counts all four. Burning crop residue puts carbon monoxide, methane and sulphur dioxide straight into the air, and the smoke's nitrogen oxides and volatile organic compounds go on to form ground-level ozone. Since 1, 2 and 4 are certain, only option (d) can be right.
- ✓ 1. Burning rice straw releases carbon monoxide; about 7% of the carbon in the straw leaves as CO.
- ✓ 2. Methane is also released; about 0.66% of the carbon in burnt rice straw is emitted as CH4.
- ✓ 3. Ozone is not emitted as such; it forms in the air from the nitrogen oxides and volatile organic compounds in stubble smoke, so it is released into the atmosphere 'due to' the burning. In any case CO, CH4 and SO2 are certain, and (d) is the only option that contains all three.
- ✓ 4. Stubble burning emits sulphur dioxide along with carbon monoxide, nitrogen oxides, methane and fine particles.
Remember · Crop-residue burning gives CO, CO2, CH4, N2O, NOx, SO2 and particulates; the smoke's VOCs and NOx then form ground-level ozone.
Sources
- Ministry of Agriculture, National Policy for Management of Crop Residues (2014), section 2.3 (Internet Archive copy) ↗ “It is estimated that upon burning, Carbon (C) present in rice straw is emitted as CO2(70% of Carbon present), CO (7%) and CH4(0.66%)”
- RSC Advances (2026): air quality and greenhouse gas emissions from rice crop burning in Punjab, 2012-2020, open-access copy on PubMed Central (NIH) ↗ “The stubble burning emits various trace gases such as particulate matter (PM 2.5 and PM 10 ), carbon dioxide (CO 2 ), carbon monoxide (CO), sulphur dioxide (SO 2 ), nitrogen oxides (NO x ), ammonia (NH 3 ), methane (CH 4 ) … In addition, the gaseous pollutants contribute to secondary aerosols and ground-level ozone.”
Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). ·