Campbell Scientific EC155 CO2 and H2O Closed-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - 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