Classical smog is

Options

A. Dark brown smog
B. yellow brown smog
C. los Angeles smog
D. Smog with secondary pollutants

Answer

**Step-by-Step Solution:**

1. **Understanding Smog**:
- Smog is a combination of fog and smoke. It is important to know this basic definition to differentiate between types of smog.

2. **Types of Smog**:
- There are two main types of smog: classical smog and photochemical smog. Recognizing the distinction between these two types is crucial for answering the question.

3. **Defining Classical Smog**:
- Classical smog is characterized by high concentrations of sulfur dioxide and particulate matter. This occurs primarily due to the combustion of fossil fuels.

4. **Color of Classical Smog**:
- Classical smog typically appears dark brown in color. This is an important identifying feature that helps differentiate it from other types of smog.

5. **Conditions for Formation**:
- Classical smog usually forms in cold or humid climates, which is another distinguishing factor from photochemical smog that forms in warm and dry climates.

6. **Identifying the Correct Option**:
- Given the options, we can analyze them:
- Option A: Dark brown smog - This is correct as classical smog is dark brown.
- Option B: Yellow brown smog - This is incorrect; this describes photochemical smog.
- Option C: Los Angeles smog - This is incorrect; this term refers to photochemical smog.
- Option D: Smog with secondary pollutants - This is vague and does not specifically describe classical smog.

7. **Conclusion**:
- The correct answer is Option A: Classical smog is dark brown smog.