Which of the following is not a common component of photo-chemical smog ?

Question

Accepted Answer

Photo-chemical smog is a type of air pollution that is formed when sunlight reacts with pollutants in the atmosphere. It is primarily composed of ozone (O₃), nitrogen oxides (NOx), and volatile organic compounds (VOCs). Let's examine why Option 4, CFCs (chlorofluorocarbons), is not a common component of photo-chemical smog, and why the other options are indeed components of it.

1. **Option 4: CFCs (Correct Answer)**
   - CFCs are not a common component of photo-chemical smog. They are primarily known for their role in ozone layer depletion in the stratosphere, not for contributing to smog formation in the troposphere. CFCs are stable compounds that do not react easily in the lower atmosphere where smog forms. Therefore, they do not participate in the chemical reactions that lead to the formation of photo-chemical smog.

2. **Option 1: Peroxyacetyl nitrate (PAN)**
   - Peroxyacetyl nitrate is a significant component of photo-chemical smog. It is formed from the reaction of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. PAN is a secondary pollutant that contributes to the eye irritation and respiratory problems associated with smog.

3. **Option 2: Ozone (O₃)**
   - Ozone is a major component of photo-chemical smog. It is formed when nitrogen oxides (NOx) and VOCs react in the presence of sunlight. Ground-level ozone is a harmful pollutant that can cause respiratory issues and other health problems, making it a key component of smog.

4. **Option 3: Nitric oxide (NO)**
   - Nitric oxide is a precursor to the formation of photo-chemical 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 the formation of ozone and other components of smog.

In conclusion, Option 4, CFCs, is correctly identified as not being a common component of photo-chemical smog. The other options, peroxyacetyl nitrate, ozone, and nitric oxide, are all integral to the formation and composition of photo-chemical smog.