ConSciR (version 0.3.0)

calcPw: Calculate Water Vapour Pressure

Description

Function to calculate water vapour pressure (hPa) from temperature (°C) and relative humidity (%).

Water vapour pressure is the pressure exerted by water vapour in a gas.

Usage

calcPw(Temp, RH, ...)

Value

Pw, Water Vapour Pressure (hPa)

Arguments

Temp

Temperature (°Celsius)

RH

Relative Humidity (0-100%)

...

Additional arguments to supply to calcPws

Details

Different formulations for calculating water vapour pressure are available:

• Arden Buck equation ("Buck")

• International Association for the Properties of Water and Steam ("IAPWS")

• August-Roche-Magnus approximation ("Magnus")

• VAISALA humidity conversion formula ("VAISALA")

The water vapor pressure (P_w) is calculated using the following equation:

$$P_w=\frac{P_{ws}\left(Temp\right)\times RH}{100}$$

Where:

• P_ws is the saturation vapor pressure using calcPws.

• RH is the relative humidity in percent.

• Temp is the temperature in degrees Celsius.

References

Wagner, W., & Pru\ß, A. (2002). The IAPWS formulation 1995 for the thermodynamic properties of ordinary water substance for general and scientific use. Journal of Physical and Chemical Reference Data, 31(2), 387-535.

Alduchov, O. A., and R. E. Eskridge, 1996: Improved Magnus' form approximation of saturation vapor pressure. J. Appl. Meteor., 35, 601-609.

Buck, A. L., 1981: New Equations for Computing Vapor Pressure and Enhancement Factor. J. Appl. Meteor. Climatol., 20, 1527–1532, https://doi.org/10.1175/1520-0450(1981)020<1527:NEFCVP>2.0.CO;2.

Buck (1996), Buck (1996), Buck Research CR-1A User's Manual, Appendix 1.

VAISALA. Humidity Conversions: Formulas and methods for calculating humidity parameters. Ref. B210973EN-O

See Also

calcMR for calculating mixing ratio

calcAD for calculating air density

calcPw for calculating water vapour pressure

calcPws for calculating water vapour saturation pressure

Examples

# Water vapour pressure at 20°C (Temp) and 50% relative humidity (RH)
calcPw(20, 50)

# Calculate relative humidity at 50%RH
calcPw(20, 50) / calcPws(20) * 100


# mydata file
filepath <- data_file_path("mydata.xlsx")
mydata <- readxl::read_excel(filepath, sheet = "mydata", n_max = 5)

mydata |> dplyr::mutate(Pw = calcPw(Temp, RH))

mydata |> dplyr::mutate(Buck = calcPw(Temp, RH, method = "Buck"),
                              IAPWS = calcPw(Temp, RH, method = "IAPWS"),
                              Magnus = calcPw(Temp, RH, method = "Magnus"),
                              VAISALA = calcPw(Temp, RH, method = "VAISALA"))