Campbell Scientific TGA100A Overview - Manual (Page 13)

TGA100A Trace Gas Analyzer Overview
The TGA100A multiple-scan mode can be used to measure suitable pairs of
gases. Typical performance for some examples is given in Table OV7.1-2.
TABLE OV7.1-2. Typical Concentration Measurement Noise
Gas Wave number
(cm -1 )
10 Hz Noise
(ppbv)
30-min Gradient
Resolution (pptv)
N
2
O 1271.077 7 140 Nitrous Oxide
and Methane CH
4
1270.785 18 360
N
2
O 2190.350 5 100
CO 2190.018 5 100
N
2
O 2203.733 1.8 35
Nitrous Oxide and
Carbon Monoxide
CO 2203.161 10 200
N
2
O 2243.110 2 40 Nitrous Oxide and
Carbon Dioxide CO
2
2243.585 400 8000
The multiple-scan mode may also be used to measure different isotopologues
of the same gas. Isotope ratio measurements are typically given in delta
notation:
1 − =
std
m
R
R
δ
where R
m
is the ratio of the isotopologue concentrations measured by the
TGA100A and R
std
is the standard isotope ratio. δ is reported in parts per
thousand (per mil or ‰). Typical isotope ratio performance is given in Table
OV7.1-3. The calibrated noise assumes a typical sampling scenario: two air
sample intakes and two calibration samples measured in a 1 minute cycle. It is
given as the standard deviation of the calibrated air sample measurements.
TABLE OV7.1-3. Typical Isotope Ratio Measurement Noise
Gas Isotope Ratio Wavenumber
(cm -1 )
10 Hz Noise Calibrated
Noise
CO
2
2293.881 0.2 ppm 0.05 ppm Carbon Dioxide,
δ 13 C only
δ 13 C 2294.481 0.5 ‰ 0.1 ‰
CO
2
2308.225 0.6 ppm 0.15 ppm
δ 13 C 2308.171 2.0 ‰ 0.4 ‰ Carbon Dioxide,
δ 13 C and δ 18 O
δ 18 O 2308.416 2.0 ‰ 0.4 ‰
H
2
O 1501.846 10 ppm 2 ppm Water,
δD only δD 1501.813 8 ‰ 2 ‰
H
2
O 1500.546 10 ppm 2 ppm
δ 18 O 1501.188 2 ‰ 0.5 ‰
Water,
δ 18 O and δD
δD 1501.116 20 ‰ 5 ‰
OV-13