35
ATMOS 41W
Teflon screen
Vapor pressure
sensor
Figure 19 Vapor pressure sensor
If the relative humidity of the air is desired, it can be computed using
Equation 1
Equation 1
RH
r ,air
=
e
a
e
s
(T
air
)
where
e
a
is the vapor pressure of the air, from the ATMOS 41W, and
e
s
(
T
air
) is saturation vapor
pressure at the air temperature given by the ATMOS 41W.
The saturation vapor pressure is calculated using the Magnus-Tetens equation (
Equation 2
)
with the following coefficients described by Buck (1981).
Equation 2
e
s
T
air
=
aexp
bT
air
c
+
T
air
⎛
⎝
⎜⎜
⎜⎜
⎞
⎠
⎟⎟⎟
⎟⎟
Water
a
= 0.611 kPa
b
= 17.502
c
= 240.97 °C
T
air
= Temperature in °C
Ice
a
= 0.611 kPa
b
= 21.87
c
= 265.5 °C
T
air
= Temperature in °C
