You have recently witnessed each of the natural phenomena listed below. Identify the natural phenomenon which does not contribute to air pollution.

Options

A. Volcanic eruptions
B. Earthquakes
C. Forest fires
D. Grass fires

Explanation

To solve the question of identifying the natural phenomenon that does not contribute to air pollution among volcanic eruptions, earthquakes, forest fires, and grass fires, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Air Pollution**: Air pollution is caused by the release of harmful substances into the atmosphere. These substances are known as air pollutants.

2. **Analyze Each Phenomenon**:
- **Volcanic Eruptions**: These release significant amounts of sulfur dioxide and carbon dioxide, both of which are air pollutants. Therefore, volcanic eruptions contribute to air pollution.

- **Earthquake**: This is a geological event characterized by the shaking of the earth. It does not produce any air pollutants as it does not involve the release of gases or particulates into the atmosphere. Thus, it does not contribute to air pollution.

- **Forest Fires**: These involve the burning of trees and vegetation, which releases carbon dioxide and nitrogen compounds into the air. Both of these can contribute to air pollution.

- **Grass Fires**: Similar to forest fires, grass fires release particulate matter and other pollutants into the air, which can cause respiratory issues and contribute to air pollution.

3. **Identify the Non-Contributor**: After analyzing all four phenomena, we find that:
- Volcanic eruptions, forest fires, and grass fires all contribute to air pollution by releasing harmful substances.
- The earthquake does not release any pollutants and therefore does not contribute to air pollution.

### Conclusion:
The natural phenomenon that does not contribute to air pollution is **earthquake**.