Question

The chief constituent of photochemical smog in metropolitan areas is

• A. SO${}_2$
• B. NO${}_2$
• C. N${}_2$O
• D. NO

Answer 1

Answer: (B)

NO${}_2$

Photochemical smog is injurious to health. The increase in air pollutants accentuates its formation. It is formed when solar radiation interacts with airborne pollutants like nitrogen oxides, or NOx, which are emitted by combustion engines in automobiles. Another pollutants are the volatile organic compounds, or VOCs, which are produced in many manufacturing processes. Nitrogen oxides and VOCs are primary pollutants.

The sun's ultraviolet light breaks down nitrogen dioxide to form nitrogen oxide and monatomic oxygen. The monatomic oxygen then combines with the oxygen already present in the atmosphere to form ozone. Chemicals, such as ozone, that result from these types of reactions are called secondary pollutants. Photochemical smog is visible mixture of secondary and primary pollutants, even though many of the individual components are invisible.

So, the correct answer is option B.