At 100% relative humidity (saturated air), the psychrometric temperatures coincide. Which statement correctly describes this condition?

Introduction / Context:
Psychrometrics uses several temperature definitions: dry-bulb (ambient), wet-bulb (adiabatic saturation surrogate), and dew point (condensation onset). At saturation (100% relative humidity), these converge, simplifying analysis for cooling coils and evaporative processes.

Given Data / Assumptions:

• Air–water vapor mixture is at thermodynamic equilibrium with liquid water.
• No measurement errors or radiation effects on thermometers.

Concept / Approach:
At saturation, the partial pressure of water vapor equals the saturation pressure at the mixture temperature. The adiabatic saturation line intersects the state point, so wet-bulb equals dry-bulb. Dew point equals the same temperature because the air is already saturated. This temperature is also the saturation temperature corresponding to that vapor pressure.

Step-by-Step Solution:

Verification / Alternative check:
On the psychrometric chart, the state point at 100% RH lies on the saturation curve where DBT, WBT, and DPT converge, confirming the statement.

Why Other Options Are Wrong:

• Options stating differences contradict saturation behavior.
• At saturation, none of the psychrometric temperatures remain distinct.

Common Pitfalls:
Confusing near-saturation (e.g., 95% RH) with exact saturation; small thermometer errors can also create apparent differences in practice.

Final Answer:
Wet-bulb temperature = Dry-bulb temperature = Dew point temperature = Saturation temperature