Appendix d. useful equations – Campbell Scientific EC150 CO2 and H2O Open-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer User Manual
Page 69
Appendix D. Useful Equations
The following table lists all the variables and constants used in the equations
below:
TABLE D-1. 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
°C
e
Vapor pressure
kPa
f
Enhancement factor
Arbitrary
d
T
Dewpoint temperature
°C
tmp
d
T
_
Temporary variable for dewpoint
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
(D-1)
(
)(
)
v
v
v
v
X
T
R
PM
X
+
+
=
1000
15
.
273
ρ
(D-2)
(
)
(
)
15
.
273
+
−
=
T
R
M
e
P
d
d
ρ
(D-3)
D-1