11th Class Chemistry Environmental Chemistry

  • question_answer 8) What are the harmful effects of photochemical smog and how they can be controlled?


    Photochemical smog causes serious health problems. Both ozone and PAN act as powerful eye irritants. Ozone and nitric oxide irritate the nose and throat and their high concentration causes headache, chest pain, dryness of throat, cough and difficulty in breathing. Compared to human beings, vegetation is more prone to harmful effects of oxidants. Ozone causes a reduction in plant growth. High concentration of ozone damages forests. Organic oxidants act as poisons to plants. Ozone may cause harm to fibres, dyes, paints and polymers. Natural rubber and synthetic polymers become brittle and crack. Smog also causes corrosion of metals, stones and building materials. Control of Photochemical Smog Many techniques are used to control or reduce the formation of photochemical smog. (i) The most straight forward way is to minimize the release of oxides of nitrogen and hydrocarbons to the atmosphere. Usually catalytic converters are used in automobiles which convert harmful gases into harmless gases and thus prevent the release of nitrogen oxide and hydrocarbons to the atmosphere. (ii) Chemical method: Smog can be suppressed by certain compounds which act as free radical traps. When these compounds are sprayed to the atmosphere, they generate free radicals which readily combine with free radical precursors of photo chemical smog. (iii) Certain plants, e.g., pinus, juniparus, quereus, pyrus and vitis can metabolise nitrogen oxide and therefore, their plantation could help in reducing nitrogen oxide from atmosphere.

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