PP Systems CIRAS-2 - Physical Constants Used in Equations; Saturated Vapor Pressure of Water from Air Temperature

Appendix 3. Photosynthesis Equations Used in CIRAS-2
CIRAS-2 Operator's Manual Version 2.04
- 160 -
Symbol
Calculated Parameter
Unit
T
leaf
Leaf Temperature
°C
Δt
Temperature difference between the air and the leaf
°C
H
Radiation absorbed by the leaf
W m
-2
r
s
Stomatal resistance to water vapor
m
2
s mol
-1
g
s
Stomatal conductance to water vapor
mmol m
-2
s
-1
C
in
CO
2
concentration of air entering cuvette
µmol mol
-1
*
C
out
CO
2
concentration of air inside and exiting the cuvette
µmol mol
-1
*
A
Rate of CO
2
Assimilation (Net Photosynthetic Rate)
µmol m
-2
s
-1
g
c
Total conductance to CO
2
transfer
mmol m
-2
s
-1
C
i
CO
2
concentration of sub-stomatal cavity
µmol mol
-1
* Determined by IRGA. Temperature and pressure corrected for water vapor effects on measurement and
analyzer temperature.
Physical Constants Used in Equations
Volume of one kg mole of gas =0.0224 m
3
, at 1013.25 millibars of pressure and 273.15 °K
Latent heat of vaporization of water ( ) = 45064.3 - (T
c
x 42.9)
Molecular weight of air (M
a
) = 28.97
Specific heat at constant pressure (C
p
) = 1.012 kJ kg
-1
K
-1
Stefan Boltzmann constant (σ) = 5.6704 x 10
-8
W m
-2
K
-4
Saturated Vapor Pressure of Water from Air Temperature
Modified from Reference 1 to optimize the fit in the temperature range of 0-50 °C, above 0 °C: