Which of the following is a secondary pollutant ?

Options

A. `CO_2`
B. `N_2O`
C. `SO_2`
D. PAN

Answer

To determine which of the given options is a secondary pollutant, we can follow these steps:

### Step 1: Understand the Definitions
- **Primary Pollutants**: These are pollutants that are directly emitted into the atmosphere from a source. Examples include carbon dioxide (CO2), sulfur dioxide (SO2), and nitrogen oxide (N2O).
- **Secondary Pollutants**: These are not emitted directly; instead, they form in the atmosphere through chemical reactions between primary pollutants.

### Step 2: Analyze the Options
1. **CO2 (Carbon Dioxide)**: This is a primary pollutant as it is directly released from sources like burning fossil fuels.
2. **N2O (Nitrous Oxide)**: This is also a primary pollutant, emitted from agricultural and industrial activities.
3. **SO2 (Sulfur Dioxide)**: This is another primary pollutant, primarily produced from the burning of fossil fuels.
4. **PAN (Peroxyacetyl Nitrate)**: This is a secondary pollutant formed from the reaction of nitrogen oxides (NOx) and hydrocarbons in the presence of sunlight.

### Step 3: Identify the Secondary Pollutant
From the analysis:
- CO2, N2O, and SO2 are all primary pollutants.
- PAN is formed through the interaction of primary pollutants, making it a secondary pollutant.

### Conclusion
The secondary pollutant among the options provided is **PAN (Peroxyacetyl Nitrate)**.

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