Question

The correct set of species responsible for the photochemical smog is:
1. N₂, NO₂ and hydrocarbons
2. CO₂, NO₂, SO₂ and hydrocarbons
3. NO, NO₂, O₃ and hydrocarbons
4. N₂, O₂, O₃ and hydrocarbons

Answer 1

Correct Answer - Option 3 : NO, NO₂, O₃ and hydrocarbons

Concept:

Photochemical smog contains oxides of nitrogen, ozone and hydrocarbons. It is also called oxidation smog.

Photochemical smog is also sometimes known as Oxidizing smog. In that it has a high concentration of oxidizing agents. Ozone is a common oxidizing agent found in photochemical smog.

NO₂ → NO + O

The resultant highly reactive atomic oxygen may combine with molecular oxygen to form a molecule of ozone (O₃).

O + O₂ → O₃

The reaction also occurs in the stratosphere, where the atomic oxygen is formed via the photolysis of O₂. Ozone is capable of reoxidizing nitric oxide to nitrogen dioxide by the thermal reaction.

O₃ + NO → NO2 + O₂

When the atmosphere is illuminated, tropospheric ozone levels increase until the rate of ozone destruction equals the photochemical production rate of ozone. During the night, ozone levels decrease because only the dark reaction can proceed. Because one molecule of NO₂ is consumed for every molecule of O₃ produced, the maximum amount of O₃ that is produced and cannot be greater than the initial amount of NO₂ present in the air.