Which of the following is not a common component of photochemical smog ?

Question

Accepted Answer

Photochemical smog is a type of air pollution that results from the reaction of sunlight with pollutants such as hydrocarbons and nitrogen oxides in the atmosphere. It is characterized by the presence of several key components, which are typically formed through complex chemical reactions.

1. **Option 4: CFC's (Chlorofluorocarbons)** - This is the correct answer because CFCs are not a common component of photochemical smog. CFCs are primarily known for their role in ozone layer depletion rather than contributing to smog formation. They are stable compounds that do not react easily in the lower atmosphere where smog forms. Instead, they rise to the stratosphere, where they release chlorine atoms that break down ozone molecules. Therefore, CFCs are not involved in the chemical reactions that produce photochemical smog.

2. **Option 1: Peroxyacetyl nitrate (PAN)** - This option is incorrect because PAN is indeed a common component of photochemical smog. It is a secondary pollutant formed from the reaction of volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight. PAN is known for its role in causing eye irritation and respiratory problems, and it is a significant component of the smog complex.

3. **Option 2: Ozone** - This option is incorrect because ozone is a major component of photochemical smog. Ground-level ozone is formed when nitrogen oxides and volatile organic compounds react in the presence of sunlight. It is a harmful pollutant that can cause respiratory issues and other health problems, and it is a key indicator of photochemical smog.

4. **Option 3: Nitric oxide (NO)** - This option is incorrect because nitric oxide is a precursor to photochemical smog. It is emitted from vehicles and industrial processes and reacts with oxygen in the atmosphere to form nitrogen dioxide (NO2), which then participates in further reactions leading to the formation of ozone and other smog components.

In summary, while peroxyacetyl nitrate, ozone, and nitric oxide are all involved in the formation and composition of photochemical smog, CFCs are not. CFCs are associated with ozone layer depletion rather than smog formation, which is why Option 4 is the correct answer.