Discuss in detail the photochemical smog emphasizing its formation, effects and mitigation. Explain the 1999 Gothenburg Protocol.

Sample Answer


Photochemical smog is a mixture of pollutants that are formed when nitrogen oxides and volatile organic compounds (VOCs) react to sunlight, creating a brown haze above cities. 



  • Nitrogen oxides produced through car fumes combine with water to form nitric acid, which then combine with molecular oxygen to produce ozone.
  • The nitric acid may precipitate to the Earth resulting in acid rain, or remain in the smog.


  • When the chemicals indoors interact with hydrocarbons, they cause eye irritation.
  • The nitrogen cycle is hampered by the atmospheric radicals because ground-level ozone cannot be removed.
  • Ozone at ground level has the potential to be exceedingly hazardous to people.
  • Decreased vision and shortness of breath.


  • Reduction of nitrogen oxide: by a process called ‘catalytic reduction’, which is used in industry and in motor vehicles
  • Reduction of VOCs: These include the use of liquefied petroleum gas (LPG) or compressed natural gas (CNG) rather than petrol


The 1999 Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-level Ozone is a multi-pollutant protocol designed to reduce acidification, eutrophication and ground-level ozone by setting emissions ceilings for sulphur dioxide, nitrogen oxides, volatile organic compounds and ammonia to be met by 2010.

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