Which of the following is a secondary air pollutant?

Options

A. Aerosol
B. CO
C. PAN
D. `CO_(2)`

Explanation

To determine which of the following is a secondary air pollutant, we need to understand the definitions and characteristics of primary and secondary pollutants.

### Step-by-Step Solution:

1. **Define Primary and Secondary Pollutants**:
- Primary pollutants are those that are emitted directly into the atmosphere from sources such as vehicles, industries, and natural events. Examples include carbon monoxide (CO), sulfur dioxide (SO2), and particulate matter.
- Secondary pollutants, on the other hand, are not emitted directly. Instead, they form in the atmosphere through chemical reactions between primary pollutants and other atmospheric components, often in the presence of sunlight.

2. **Identify the Options**:
- The options provided are:
- A) Aerosol
- B) Carbon monoxide (CO)
- C) PAM (Peroxyacetyl nitrate)
- D) Carbon dioxide (CO2)

3. **Analyze Each Option**:
- **Aerosol**: This term generally refers to tiny solid or liquid particles suspended in the air. Aerosols can be primary or secondary depending on their source.
- **Carbon monoxide (CO)**: This is a primary pollutant, as it is emitted directly from sources like vehicle exhaust.
- **PAM (Peroxyacetyl nitrate)**: This is a secondary pollutant formed from the reaction of primary pollutants (like volatile organic compounds and nitrogen oxides) in the presence of sunlight.
- **Carbon dioxide (CO2)**: This is primarily a product of combustion and is considered a primary pollutant, although it can also be involved in secondary reactions.

4. **Conclusion**:
- Among the options, PAM (Peroxyacetyl nitrate) is identified as a secondary air pollutant because it is formed through the interaction of primary pollutants with atmospheric gases.

### Final Answer:
The correct answer is C) PAM (Peroxyacetyl nitrate).

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