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

Options

A. Ozone
B. Acrolein
C. Peroxyacetyl nitrate
D. Chlorofluorocarbone

Explanation

To determine which of the following is not a common component of photochemical smog, we need to analyze each option provided:

1. **Nitrous Oxide (NO₂)**: This is a common component of photochemical smog. It is produced from vehicle emissions and industrial processes. In the presence of sunlight, nitrous oxides react with volatile organic compounds (VOCs) to form ozone.

2. **Ozone (O₃)**: Ozone is a significant component of photochemical smog. It is formed when sunlight reacts with pollutants such as nitrous oxides and VOCs. Ozone contributes to the brownish color of smog.

3. **Peroxacetyl Nitrate (PAN)**: PAN is also a component of photochemical smog. It is formed from the reaction of ozone with VOCs and is known to contribute to the harmful effects of smog.

4. **Chlorofluorocarbons (CFCs)**: CFCs are not a common component of photochemical smog. They are primarily known for their role in ozone depletion in the stratosphere rather than contributing to ground-level smog.

Based on this analysis, the answer to the question "Which of the following is not a common component of photochemical smog?" is **Chlorofluorocarbons (CFCs)**.

### Final Answer:
**Chlorofluorocarbons (CFCs)**