Campbell Scientific IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer - Manual (Page 59)

Appendix B. Equations
TABLE B-1 lists variables and constants used in the following equations.
TABLE B-1. Table of Equation 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·m 3 ·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 1 )
( )( )
v
v v
v X T R
PM X
+ +
=
1000 15 . 273
ρ
(B-2 1 )
( )
( )
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