Previous Year Question

Burning crop and biomass residues produces several gaseous and particulate air pollutants.

Their type and quantity depend on the moisture content, chemical composition of the residue, combustion temperature and availability of oxygen.

Carbon monoxide: Inadequate availability of oxygen causes incomplete combustion of biomass, resulting in the production of carbon monoxide.

Carbon monoxide emissions can be particularly high during smouldering or low-temperature combustion.

Carbon monoxide can bind with haemoglobin in the blood and reduce the oxygen-carrying capacity of the body.

Methane: During incomplete combustion of crop residues, particularly in the smouldering stage, some carbon is not oxidised completely and methane may be produced.

Methane is a powerful greenhouse gas and also plays an indirect role in the formation of tropospheric ozone.

Ozone: Biomass burning releases ozone-precursor pollutants such as carbon monoxide, nitrogen oxides and volatile organic compounds.

Photochemical reactions between these precursor pollutants in the presence of sunlight produce tropospheric ozone.

Therefore, ozone should primarily be understood not as a primary pollutant emitted directly from the combustion source but as a secondary pollutant formed due to biomass burning.

Sulphur dioxide: Oxidation of sulphur-containing compounds present in plants and crop residues may produce sulphur dioxide.

Its emission depends on the sulphur content of the residue and is generally lower than that from high-sulphur fossil fuels.

Apart from these pollutants, crop-residue burning also releases PM₂.₅, PM₁₀, black carbon, nitrogen oxides and volatile organic compounds.

These pollutants may contribute to smog, reduced visibility, respiratory problems and climate change.

Therefore, all four listed pollutants may be directly emitted or secondarily formed in the atmosphere due to crop/biomass-residue burning.