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Photochemical smog is a resultant of the reaction among

June 1, 2025 by rawan239

Photochemical smog is a resultant of the reaction among

NO₂, O₃ and peroxyacetyl nitrate in the presence of sunlight

CO, O₂ and peroxyacetyl nitrate in the presence of sunlight

CO, CO₂ and NO₂ at low temperature

high concentration of NO₂, O₃ and CO in the evening

This question was previously asked in

UPSC IAS – 2013

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Photochemical smog is a complex mixture of air pollutants that forms when sunlight reacts with certain chemicals in the atmosphere. Key components and precursors include nitrogen oxides (NOx) and volatile organic compounds (VOCs). The resulting smog contains pollutants like ozone (O₃), peroxyacetyl nitrate (PAN), and aldehydes.

The formation of photochemical smog is driven by sunlight. Nitrogen dioxide (NO₂) is a primary pollutant that photodissociates in sunlight to form nitric oxide (NO) and atomic oxygen (O). This atomic oxygen quickly reacts with molecular oxygen (O₂) to form ozone (O₃). VOCs react with NOx and other atmospheric components in the presence of sunlight to form a variety of secondary pollutants, including PAN. Therefore, NO₂, O₃ (as a product), and PAN (as a product), with sunlight as the driving force, are central to photochemical smog.

Photochemical smog is often referred to as “Los Angeles smog” because it was first recognized in Los Angeles. It differs from traditional “London smog” (sulfurous smog), which is caused by the burning of fossil fuels containing sulfur and occurs under cool, humid conditions. Photochemical smog is more common in sunny, dry climates with significant vehicular traffic.

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