Appendix b. useful equations – Campbell Scientific EC155 CO2 and H2O Closed-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer User Manual
Page 59
Appendix B. Useful Equations
The following table lists all the variables and constants used in the equations
below:
Table of Variables and Constants
Variable or Constant
Description
Units
c
ρ
CO
2
Mass Density
mg m
-3
v
ρ
H
2
O Mass Density
g m
-3
d
ρ
Mass Density of Dry Air
g m
-3
c
X
CO
2
Molar Mixing Ratio
(concentration relative to dry air)
µmol mol
-1
v
X
H
2
O Molar Mixing Ratio
(concentration relative to dry air)
mmol mol
-1
c
M
Molecular Weight of CO
2
44 mg mmol
-1
d
M
Molecular Weight of dry air
0.029 g mmol
-1
v
M
Molecular weight of H
2
O
0.018 g mmol
-1
P
Ambient Pressure
kPa
R
Universal Gas Constant
8.3143×10
–6
kPa m3 K
–1
mmol
–1
T
Ambient Temperature
o
C
e
Vapor Pressure
kPa
f
Enhancement Factor
Arbitrary
d
T
Dew Point Temperature
o
C
tmp
d
T
_
Temporary variable for dew point
calculation
Arbitrary
Mass Density from Molar Mixing Ratios
(
)
−
+
=
v
v
c
c
c
M
T
R
P
M
X
ρ
ρ
15
.
273
10
6
(B-1)
(
)(
)
v
v
v
v
X
T
R
PM
X
+
+
=
1000
15
.
273
ρ
(B-2)
(
)
(
)
15
.
273
+
−
=
T
R
M
e
P
d
d
ρ
(B-3)
(
)
15
.
273
1000
+
+
−
=
T
R
M
X
P
X
P
d
v
v
d
ρ
(B-4)
B-1