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Introduction
Vapor Pressure
Humidity Equations and Conversion Chart
The following symbols appear in the equations below:
e = Vapor Pressure, millibars
e
= Vapor Pressure with respect to ice, millibars
i
e
= Vapor Pressure with respect to water, millibars
w
e
= Saturation vapor pressure, ice, millibars
is
e
= Saturation vapor pressure, water, millibars
ws
P = Total Pressure, millibars
T = Temperature, °C
T
= Ambient temperature, °C
a
T
= Dew point temperature, °C
d
T
= Frost point temperature, °C
f
Saturation vapor pressure with respect to water is a function of
temperature only and is given by the following:
Saturation vapor pressure with respect to ice requires a minor
adjustment of the constants as given by the following:
In addition to yielding saturation vapor pressure as a function of
ambient temperature, the above equations also yield ambient vapor
pressure as a function of dew/frost point.
The total pressure of a gas mixture is equal to the sum of the partial
pressure each gas would exert, were it to occupy the same total
volume, according to Dalton's law.
6.1121EXP 17.502T
E
=
----------------------- -
WS
240.97 T
6.1115EXP 22.452T
E
=
----------------------- -
IS
272.55 T
October 2007
(B-1)
+
(B-2)
+
B-1
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