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PAN (Peroxyacetyl nitrate) is an important constituent of photochemical smog. It is
A. Primary pollutant
B. Secondary pollutant
C. Natural pollutant
D. Corollary pollutant

Last updated date: 20th Jun 2024
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Hint: Smog is the opaque or dark fog that is a combination of dust, water vapour, and a mixture of gases. Photochemical smog is formed in the congested cities with lots of traffic where warm conditions due to intense solar radiations are present.

Complete answer: Photochemical smog is a mixture of gases like ozone, PAN (Peroxyacetyl nitrate), and different nitrogen oxides \(\left({N{O_X}} \right)\). It is called the brown air and the grey air when the solar radiation is lesser and intense. The ozone of the photochemical smog corrodes the heritage building surfaces and damages the marble structures. On the other hand, the PAN inhibits the process of ETS (or Electron Transport System) in plants and damages the chloroplast. The PAN is the secondary air pollutant. Air pollutants are mainly of two types. They are classified based on the form of pollutants in which they persist after their release. These two types are:
a) Primary pollutants – These pollutants are emitted directly into the environment from definite sources. For example – Metal particles, DDT, carbon, tar, resin, sulphur compounds, carbon compounds, nitrogen compounds, pollen, fungi, plastics, bacteria, etc.
Secondary pollutants – These pollutants are formed by the reactions of the primary pollutants in the environment. For example – PAN, Ozone, etc.
Thus, based on the above information we can conclude that PAN is a secondary pollutant.
Hence, the correct answer is option B.

Note: The second category of smog is also present. It is known as the ‘London smog’. The London smog is also known as the classical smog. This smog occurs at lower temperatures. London smog contains a mixture of harmful gases like Hydrogen sulfide and Sulfur dioxide. It has a reducing type of environment and it is dark brown. The secondary type of pollutants has no role in causing it and it is solely caused by the primary pollutants.