OPENÕs System Variables
Band Broadening Correction for Water Vapor
14-24
Using the LI-6400
14
In principle, (14-36) can be solved for mole fraction, giving
(14-37)
Since LI-COR gas analyzers produce an output voltage that is proportional to
absorptance,
(14-38)
substituting (14-38) into (14-37) yields
(14-39)
where
C
is the CO
2
mole fraction in µmol mol
-1
, and the constant
K
is includ-
ed in the calibration function
f
;
P
0
= 101.3 kPa,
T
0
is the fundamental LI-COR gas analyzer calibration function, and
f(x)
takes
the form of a polynomial. Note the difference in how temperature and pres-
sure affect the calibration curve for a LI-COR gas analyzer: temperature
serves as a concentration scaling factor, while pressure scales the raw voltage,
much like a gain adjustment.
All gases are not equally effective in causing pressure broadening of absorp-
tion lines. The equivalent pressure
P
e
is defined as
(14-40)
where
is the partial pressure of nitrogen, and
P
i
gives the partial pres-
sures of other diluent non-absorbing gases. The partial pressure of each non-
absorbing gas is multiplied by a weighting factor
called the foreign gas
broadening coefficient. The coefficients
reflect the ability of each diluent
gas to cause pressure broadening relative to
;
b
is the self-broadening co-
efficient for the absorbing gas, and it gives the relative effect of its own partial
pressure on absorption (Burch et al., 1962).
Broadening coefficients for the effect of various gases on CO
2
absorption at
4.26 µm are given in Table 14-9. For example, the equivalent pressure of a
X
h
1
Ð
A
P
---
( )
T
=
V
KA
=
C
f V
P
0
P
------
(
)
T
T
0
-------
=
P
e
P
N
2
a
i
P
i
å
b
CO
2
+
+
=
P
N
2
a
i
a
i
a
N
2
Summary of Contents for LI-6400
Page 1: ...Using the LI 6400 Portable Photosynthesis System ...
Page 15: ...Part I The Basics ...
Page 16: ......
Page 174: ...Making Measurements Answers to Questions 4 56 Using the LI 6400 4 ...
Page 175: ...Part II Useful Details ...
Page 176: ......
Page 200: ...Standard Tools Power ON Hooks 5 24 Using the LI 6400 5 ...
Page 214: ...Real Time Data Real Time Graphics 6 14 Using the LI 6400 6 ...
Page 234: ...Environmental Control Light Control 7 20 Using the LI 6400 7 ...
Page 244: ...Light Sensor Considerations Gallium Arsenide Phosphide GaAsP Sensor 8 10 Using the LI 6400 8 ...
Page 288: ...Data Logging Making Your Own AutoPrograms 9 44 Using the LI 6400 9 ...
Page 289: ...Part III Working With Files ...
Page 290: ......
Page 312: ...The LPL File System Troubleshooting 10 22 Using the LI 6400 10 ...
Page 340: ...Downloading Files Using a Data Capture Program 11 28 Using the LI 6400 11 ...
Page 375: ...Part IV Configuration Issues ...
Page 376: ......
Page 420: ...Defining User Variables Old Style vs New Style 15 18 Using the LI 6400 15 ...
Page 454: ...Using an Energy Balance Further Reading 17 12 Using the LI 6400 17 ...
Page 455: ...Part V Maintenance Troubleshooting ...
Page 456: ......
Page 572: ...Troubleshooting Useful Information 20 46 Using the LI 6400 20 ...
Page 593: ...Part VI Programming ...
Page 594: ......
Page 622: ...Programming with LPL Compiler Directives 22 28 Using the LI 6400 22 ...
Page 846: ...Index I 16 Using the LI 6400 ...