PP Systems CIRAS-3 - Physical Constants Used in Equations; Definition of Symbols; Measured Parameters; Calculated Parameters

CIRAS-3 Operation Manual V. 1.09 163 support@ppsystems.com
Physical Constants Used in Equations
• Volume of one kg mole of gas =0.0224 m
3
, at 1013.25 millibar barometric pressure and 273.15 °K
• Latent heat of vaporization of water ( λ ) = 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
Definition of Symbols
Measured Parameters
Symbol
Parameter
Unit
V
20
Flow rate of dry air into cuvette at STP
cc sec
-1
A
Projected leaf area
cm
2
r
b
Boundary layer resistance to water vapor
m
2
s mol
-1
P
Atmospheric pressure
mb
Q
Photon flux density incident on cuvette
µmol m
-2
s
-1
T
c
Cuvette air temperature
°C
Calculated Parameters
Symbol
Parameter
Unit
W
Mass flow of dry air per unit leaf area
mol m
-2
s
-1
e
in
Partial pressure of water vapor of air entering cuvette
mb *
e
out
Partial pressure of water vapor of stirred cuvette air
mb *
E
Transpiration rate
mmol m
-2
s
-1
e
s
Saturated vapor pressure at cuvette air temperature
mb
e
leaf
Saturated vapor pressure (inside the leaf) at leaf temperature
mb
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
CO
2
Assimilation rate (net photosynthesis)
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
* Detected by IRGAs, temperature and pressure corrected, effects of foreign gas broadening (water vapor
effects) on measurement corrected.