Which of the following is a major cause of air pollution ?

Question

UnlockIAS · Accepted Answer

Correct — A, Burning of fossil fuels. Combustion of coal, petroleum products and natural gas in power stations, vehicles, industrial boilers, brick kilns and household stoves is the single largest human source of air pollution, and it is the only option here whose primary output goes straight into the atmosphere. What comes out of a flame is a standard list: sulphur dioxide from the sulphur in coal and diesel, oxides of nitrogen formed when atmospheric nitrogen is oxidised at high flame temperatures, carbon monoxide and unburnt hydrocarbons from incomplete combustion, and fine particulate matter — the PM2.5 and PM10 that the Air Quality Index actually measures. Those primary emissions then react in sunlight to make secondary pollutants: ground-level ozone and peroxyacetyl nitrate in photochemical smog, and sulphate and nitrate aerosols that fall out as acid rain. The dominance is not a textbook generalisation but a measured one — the United States Environmental Protection Agency attributes the largest share of sulphur dioxide emissions to power plants burning fossil fuels, and India's own Air Quality Index is built around carbon monoxide, nitrogen dioxide, sulphur dioxide, ozone, PM2.5, PM10, ammonia and lead, of which the combustion-derived species are the majority. The other three options are real environmental problems whose principal medium is soil, water or the biosphere rather than air; each touches air only through a secondary or indirect pathway, which is the distinction the word 'major' is testing.

Why the other options are wrong — (b) Plastic disposal is chiefly a land and marine pollution problem — landfill accumulation, drain blockage, microplastics in rivers and oceans. It becomes an air problem only when plastic is set alight, which releases dioxins, furans and particulates; that is open burning, a different act from disposal, and it is why municipal rules prohibit it.  (c) Pesticide overuse is a soil and water contamination issue — residues in groundwater, runoff into ponds and rivers, and biomagnification up the food chain, the classic DDT story. Spray drift and volatilisation do put some pesticide into the air locally, but nothing on the scale or geographic reach of combustion emissions.  (d) Felling forests removes a carbon sink and exposes soil to wind erosion, so it worsens dust and raises atmospheric carbon dioxide indirectly. But it emits no pollutant of its own unless the clearing is done by fire; it takes away an absorber rather than adding a source, which is a different mechanism from the one the question is after.

Concept: Air pollutants are classified two ways, and both classifications matter for questions like this. By origin, a primary pollutant is emitted directly — sulphur dioxide, oxides of nitrogen, carbon monoxide, particulate matter, unburnt hydrocarbons — while a secondary pollutant is formed in the atmosphere from primary ones, such as ground-level ozone and peroxyacetyl nitrate in photochemical smog, or the sulphuric and nitric acids of acid rain. By source, pollution is either natural (volcanic ash, forest fires, dust storms, pollen) or anthropogenic. Fossil-fuel combustion sits at the head of the anthropogenic list because it produces primary pollutants in every one of those chemical families at once, in enormous volume, and continuously. India measures the result through the National Air Quality Index, which reports eight pollutants — PM2.5, PM10, nitrogen dioxide, sulphur dioxide, carbon monoxide, ozone, ammonia and lead — on a 0 to 500 scale.

State PCS 2024 Q129 — Environment & Ecology PYQ with Answer

State PCS 2024 Q129 — Environment & Ecology PYQ with Answer