Specific Humidity Calculator G/Kg Formula

Specific Humidity Formula:

\[ SH = 0.622 \times \frac{Pw}{P - Pw} \times 1000 \]

Specific Humidity (SH):

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1. What is Specific Humidity?

Specific humidity is defined as the mass of water vapor per unit mass of moist air. It is typically expressed in grams of water vapor per kilogram of air (g/kg). Unlike relative humidity, specific humidity is not temperature-dependent, making it a more precise measure of the actual moisture content in air.

2. How Does the Calculator Work?

The calculator uses the specific humidity formula:

\[ SH = 0.622 \times \frac{Pw}{P - Pw} \times 1000 \]

Where:

\( SH \) — Specific humidity (g/kg)
\( Pw \) — Water vapor pressure (Pa)
\( P \) — Total air pressure (Pa)
0.622 — Ratio of molecular weight of water vapor to dry air
1000 — Conversion factor from kg to g

Explanation: The formula calculates the mass mixing ratio of water vapor to dry air, then converts it to grams per kilogram.

3. Importance of Specific Humidity Calculation

Details: Specific humidity is crucial in meteorology, climate studies, and HVAC applications. It helps in weather forecasting, understanding atmospheric processes, and designing climate control systems.

4. Using the Calculator

Tips: Enter water vapor pressure and total air pressure in Pascals (Pa). Both values must be positive, and total pressure must be greater than water vapor pressure.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between specific humidity and relative humidity?
A: Specific humidity measures the actual moisture content (g/kg), while relative humidity expresses how close the air is to saturation at a given temperature (%).

Q2: Why use Pascals as the pressure unit?
A: Pascals are the SI unit for pressure. The formula works with any consistent pressure units, but inputs must be in the same units.

Q3: What are typical specific humidity values?
A: Values range from near 0 g/kg in dry deserts to about 20 g/kg in very humid tropical regions.

Q4: Can I use hPa instead of Pa?
A: Yes, but ensure both pressure values use the same units (1 hPa = 100 Pa).

Q5: Why is the constant 0.622 used?
A: It represents the ratio of the molecular weight of water vapor (18.015 g/mol) to that of dry air (28.965 g/mol).