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USER MANUAL | ICOS | INSTRUCTIONS | UM/ICOS-EN REV. B.2
127
Appendix I:Isotope Definitions
The CCIA measures the concentration of
12
CO
2
,
13
CO
2
, and OC
18
O. These concentrations are
used to calculate the total CO
2
and the isotope ratios that are reported on the display
screens. The data file output includes the concentrations as well. The terms and their
respective data file name are listed below:
The isotope ratios are reported in ‰ relative to Vienna Pee Dee Belemnite converted to
CO
2
(VPDB-CO2). The standards listed below were taken from IAEA-TECDOC-825.
(R
13
) VPDP-CO
2
0.0112372
(R
18
) VPDP-CO
2
0.002088349077
Total CO
2
is defined as the sum of all the isotopes:
CO
2=
[
16
O
12
C
16
O]+ [
16
O
13
C
16
O]+ [
16
O
12
C
18
O]
The isotope ratios are defined according to:
𝛿
13𝐶
=
(
𝑅
13
)
𝑀𝑒𝑎𝑠
( 𝑅
13
)
𝑉𝑃𝐷𝐵−𝐶𝑂2
− 1 × 1000
𝛿
18𝑂
=
(
𝑅
18
)
𝑀𝑒𝑎𝑠
( 𝑅
18
)
𝑉𝑃𝐷𝐵−𝐶𝑂2
− 1 × 1000
CO
2
X_CO2__ppm

13
C
D13C_VPDB_CO2

18
O
D18O_VPDB_CO2
[
16
O
12
C
16
O]
X_CO2_626__ppm
[
16
O
13
C
16
O]
X_CO2_636__ppm
[
16
O
12
C
18
O]
X_CO2_628__ppm