USER MANUAL | ICOS | INSTRUCTIONS | UM/ICOS-EN REV. B.2
124
Appendix J:
Isotope Definitions
The GLA351-CCIA3 measures the concentration of
12
CO
2
,
13
CO
2
, OC
18
O, and OC
17
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
(R
17
) VPDP-CO
2
0.000380803342
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]+ [
16
O
12
C
17
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
𝛿
17𝑂
=
(
𝑅
17
)
𝑀𝑒𝑎𝑠
(
𝑅
17
)
𝑉𝑃𝐷𝐵−𝐶𝑂2
−
1 × 1000
Where the measured ratios are calculated from the measured concentrations:
(
𝑅
13
)
𝑀𝑒𝑎𝑠
=
𝐶
13
𝐶
12
=
[
𝑂
16
𝐶
13
𝑂
16
]
[
𝑂
16
𝐶
12
𝑂
16
]
CO
2
X_CO2__ppm
13
C
D13C_VPDB_CO2
18
O
D18O_VPDB_CO2
17
O
D17O_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
[
16
O
12
C
17
O]
X_CO2_627__ppm
