Civil Services Prep

Prelims 2013 · Environment · Question 99

Photochemical smog is a resultant of the reaction among

  1. NO2, O3 and peroxyacetyl nitrate in the presence of sunlight
  2. CO, O2 and peroxyacetyl nitrate in the presence of sunlight
  3. CO, CO2 and NO2 at low temperature
  4. high concentration of NO2, O3 and CO in the evening

Answer

NO2, O3 and peroxyacetyl nitrate in the presence of sunlight

  • (a) Photochemical smog forms when NOx and hydrocarbons react in sunlight, producing secondary pollutants like ozone (O3) and peroxyacetyl nitrate (PAN). Verdict: Correct.
  • (b) CO, O2 and PAN are not the standard precursor set for photochemical smog; the key reactants are nitrogen oxides and hydrocarbons/VOCs under sunlight. Verdict: Incorrect.
  • (c) CO, CO2 and NO2 at low temperature do not describe photochemical smog formation; this is not a sunlight-driven oxidant-smog combination. Verdict: Incorrect.
  • (d) Photochemical smog is associated with sunlight-driven daytime reactions, not simply high evening concentrations of gases. Verdict: Incorrect.
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