How is industrial smog formed? Why is it grey in colour?

Explanation

### Step-by-Step Solution:

1. **Understanding Industrial Smog Formation**:
- Industrial smog is primarily formed from the burning of fossil fuels, particularly coal. When coal is burned, it releases smoke and sulfur dioxide (SO2) into the atmosphere.

2. **Combination with Fog**:
- The smoke and sulfur emissions do not remain isolated. They combine with water vapor in the air, especially during cooler weather when fog is present. This combination leads to the formation of industrial smog.

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