Psychrometrics terminology The wet-bulb depression (DBT − WBT) is primarily an indicator of which humidity measure of air?

Introduction / Context:
Wet-bulb depression—the difference between dry-bulb temperature (DBT) and wet-bulb temperature (WBT)—is widely used in field measurements to estimate moisture content and comfort conditions.

Given Data / Assumptions:

• DBT measured with a standard dry thermometer.
• WBT measured with a wetted wick and adequate air motion.
• Near-atmospheric pressure; ideal gas approximation for moist air.

Concept / Approach:
As relative humidity (RH) decreases (air becomes drier), evaporation from the wet bulb increases, lowering WBT and enlarging the depression. Conversely, as RH approaches 100%, WBT → DBT and the depression tends to zero.

Step-by-Step Solution:
Compute depression: ΔT = DBT − WBT.Interpretation: large ΔT → strong evaporative potential → low RH.Therefore, wet-bulb depression is primarily an indicator of relative humidity.

Verification / Alternative check:
Psychrometric tables convert DBT and WBT directly to RH; a one-to-one mapping exists for fixed barometric pressure.

Why Other Options Are Wrong:

• Absolute/specific humidity depend on total moisture content but are not read directly from the depression alone without charts/tables.
• Adiabatic saturation temperature is a related concept but not the quantity indicated by the depression per se.

Common Pitfalls:
Interpreting depression without accounting for barometric pressure in precise calculations; however, qualitatively it reflects RH.

Final Answer:
Relative humidity