Dew point is not affected by

Analyze the question: We are asked which factor does not affect the dew point.

Concept: The dew point is the temperature at which air becomes saturated with water vapour, so that condensation (dew) begins to form. It depends on:

• The amount of water vapour in the air. More vapour means a higher dew point, and less vapour means a lower dew point. This is the main factor.
• Atmospheric pressure. The saturation vapour pressure and the partial pressure of the vapour depend on the surrounding pressure, so changes in pressure shift the dew point slightly.
• Air temperature. This is related indirectly. The air temperature determines how close the air is to its dew point, and it affects how much vapour the air can hold, so it is usually treated as a related factor in textbook questions.

Step by step:

1. Option C (amount of water vapour): this directly determines the dew point, so it does affect it.
2. Option D (atmospheric pressure): this changes the vapour pressure and the saturation conditions, so it affects it.
3. Option A (temperature): it is linked to saturation and humidity, so it is considered to have an effect.
4. Option B (wind): wind only moves air around and speeds up evaporation or mixing. It does not change the dew point of a given sample of air.

Note on the answer: Strictly speaking, temperature does not change the dew point of a fixed sample of air at constant pressure. The dew point depends on moisture content and pressure. So A could be argued as well. Wind is the factor that is clearly unrelated, because it is not a property of the air's moisture content or pressure. My working agrees with the key that B is the best answer.

Correct answer: B (wind)

Tip: Remember that dew point depends on moisture and pressure. If an option is about air movement (wind), it is the "not affected" choice.