Question

The chief constituent of photochemical smog is
1. NO₂ gas
2. None of these
3. PAN
4. Both 1 and 3

Answer 1

Correct Answer - Option 1 : NO₂ gas

Concept:

Photochemical Smog

• Photochemical smog is formed when ultraviolet light from the sun reacts with nitrogen oxides in the atmosphere.
• Photochemical smog is a brownish-gray haze caused by the action of solar ultraviolet radiation on the atmosphere polluted with hydrocarbons and oxides of nitrogen.
• It contains anthropogenic air pollutants, mainly ozone, nitric acid, and organic compounds, which are trapped near the ground by temperature inversion. These pollutants and also some others can affect human health and cause damage to plants.
• Photochemical smog often has an unpleasant odor due to some of its gaseous components.
• Photochemical smog is also known as “Los Angeles smog. 
• Nitric oxide (NO) and nitrogen dioxide (NO₂) are emitted from the combustion of fossil fuels, along with being naturally emitted from things such as volcanos and forest fires. These are main constituent of the photochemical smog.
• When exposed to ultraviolet radiation, NO₂ goes through a complex series of reactions with hydrocarbons to produce the components of photochemical smog—a mixture of ozone, nitric acid, aldehydes, Peroxyacyl nitrates (PANs) and other secondary pollutants.

Conclusion:

So the main constituent is NO2 gas.