Campbell Scientific EC150 CO2 and H2O Open-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - 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