Question

Which one of the following pollutants or pairs of pollutants is formed due to photochemical reactions?

• A. CO alone
• B. O\(_3\) and PAN
• C. PAN and NH\(_3\)
• D. NH\(_3\) and CO

Hint:

Photochemical smog contains ozone and PAN, both of which are secondary pollutants formed by sunlight-driven reactions involving NO\(_x\) and VOCs.

Answer 1

The Correct Option is B

Photochemical reactions in the atmosphere occur when sunlight reacts with nitrogen oxides (NO\(_x\)) and volatile organic compounds (VOCs), leading to the formation of secondary pollutants. Two key secondary pollutants formed by these reactions are:
- Ozone (O\(_3\)): Although O\(_3\) is beneficial in the stratosphere (ozone layer), ground-level ozone is a harmful air pollutant formed by sunlight-driven reactions involving NO\(_x\) and VOCs.
- Peroxyacetyl Nitrate (PAN): This is a component of photochemical smog. PAN is formed through a reaction involving hydrocarbons and nitrogen oxides in the presence of sunlight.
Other substances like CO (carbon monoxide) and NH\(_3\) (ammonia) are not formed through photochemical reactions. CO is primarily a product of incomplete combustion, and NH\(_3\) is released from agricultural activities and waste treatment, not from atmospheric chemical reactions involving sunlight.
Hence, O\(_3\) and PAN are the correct answer.