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UPSC Prelims 1993 · Environment · Pollution Files
Acid precipitation is now regarded as a serious problem in some European and Asian countries. Its major cause or source is
- (a) discharge of acidic effluents onto neutral or slightly alkaline land where the acidic components precipitate
- (b) emissions of Sulphur oxides and nitrogen oxides from thermal power plants and burning of fossil fuels; these oxides dissolve in atmospheric water vapour and fall back on earth as acid rain
- (c) natural carbon dioxide released during respiration of living organisms dissolves in water, forming carbonic acid which is the chief contributor to acidity in rain water
- (d) chloro-fluoro-carbons readily react with various chemicals near the earth's surface, producing acidic intermediates which cause acid precipitation
Show the answer and explanation
Answer: (b) emissions of Sulphur oxides and nitrogen oxides from thermal power plants and burning of fossil fuels; these oxides dissolve in atmospheric water vapour and fall back on earth as acid rain
SO₂ and NOₓ from power plants and fuel burning dissolve in cloud water and fall as acid rain.
The idea
“Acid deposition” is wider than acid rain: it includes wet deposition in rain, snow and fog, and dry settling of acidic gases and particles. The pollution travels with the wind, so the country that suffers is often not the country that burnt the coal.
Power plants burn coal → SO₂ and NOₓ rise from tall chimneys → Winds carry them across borders → They turn into acids in the air → Fall as acid rain or snow far away
Why the others are wrong
(a) Acid effluents on land are water or soil pollution, not acid rain.
(c) CO₂ from respiration makes rain only mildly acidic (pH 5.6) — that is natural.
Also know
Lakes in Sweden and Norway were damaged by emissions from Britain and Germany. This led to the 1979 Convention on Long-Range Transboundary Air Pollution, the first treaty on air pollution across borders. Europe and North America then cut sulphur with low-sulphur fuel and scrubbers; the problem has since shifted to Asia.
🔒 Acid rain = SO₂ + NOₓ from fossil fuels; damages lakes, forests, monuments.