London smog is ............... in nature.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the nature of London smog. To answer this, we need to identify the characteristics and composition of London smog.

2. **Identifying London Smog**: London smog is also known as "sulphurous smog." This name indicates that it has a significant amount of sulfur compounds in its composition.

3. **Formation of London Smog**: London smog is formed due to high concentrations of sulfur oxides, particularly sulfur dioxide (SO₂), which are released into the atmosphere primarily from the burning of sulfur-bearing fossil fuels, such as coal.

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