InGOS:
Questionnaire for evaluation of "historic" and recent Non-CO2
Greenhouse Gases measurements in Europe
1. System overview
The calibration strategy used for GC measurements at DEC station is the
one identified as instrument response function (IRF).
The instrument response functions are determined frequently (approx. once
every 3 days) via a set of calibrated tanks, hereafter referred to as
“response function standards” (RFS). The response function links peak
area/height to the corresponding calibrated mole fraction, considering the
nonlinearities of the instrument. Potential temporal changes of the
nonlinearities are accounted for by the high frequency of the RF
determinations. To account for short‐term environment changes in the
laboratory a hereafter called “working ‐tank” (WT) is measured alternating
to the samples. This working tank is afterwards used to normalize the
sample signals.
The calibration scales, the covered ranges, as well as the number of primary
laboratory standards are specified in Table 1.
Table 1 Overview of the GC system, calibration and QC strategies.
Station name:
DEC
Responsible PI:
Josep-Anton Morguí
Organisation:
IC3
Email:
[email protected] / [email protected]
Methane
Nitrous Oxide
Start of measurements:
01/2013
01/2013
Instrument type:
Agilent 6890N_FID
Agilent 6890N_microECD
Drying system:
Nafion + Cryocooler -70ºC
Nafion + Cryocooler -70ºC
Calibration scheme:
Instrument response function
Instrument response function
Calibration scale:
NOAA-2004
NOAA-2006A
Calibration range:
1698.4 - 2098.00 ppb
309.48 - 332.04 ppb
Nº of primary lab. standards:
7 (not used to calibrate WT)
7 (not used to calibrate WT)
Calibration:
1
Frequency of working tank
measurements:
Once every 16 min
Once every 16 min
Measurement
pattern:
A=ambient; WT(n)=working
tank; RFS=response function
standard
WT-A-WT-A- … - [WT – RFS#1]
(x6) - [WT – RFS#2] (x6) –
etc.
WT-A-WT-A- … - [WT – RFS#1]
(x6) - [WT – RFS#2] (x6) –
etc.
Frequency
of
response
function measurements:
Once every 3 days
Once every 3 days
Nº
of
calibrated
mole
fractions per resp. func. det.
6 -> 2 -> 4
6 -> 2 -> 4
Since the beginning
Since the beginning
No
No
Quality assurance checks:
Target gas:
Co-located
measurements:
flasks
Intercomp. activities at the station:
Cucumbers
Yes (once)
Yes (once)
2. Working tanks and Response function standards
Each changeover as well as the assigned mole fractions of the used working
tanks (WT) and the response function standards (RFS) are listed in Tables 23.
Several information is included in these tables, i.e. the composition of the
gas mixture in the tanks, how it was filled (ambient air, spiked ambient air
or artificial mixture), as well as the tank material (aluminium (alu), stainless
steel (ss) or any other).
We refer all our measurements to the response function standards (RFS).
Concentration values of the WTs are not used to derive sample or target
concentrations.
The RFS tanks used so far were calibrated in the MPI Jena laboratory
(D86038#; where # 1:7) and those RFS which were prepared by the
commercial company Praxair (PXS283641, PXS259614) were calibrated
against six NOAA tanks twice during 2 different days in November 2014 at
DEC station using the same GC instrument.
Table 2. Changes and parameters of working tanks (WT).
2
First working tank
Worki
ng
tank
ID
Filling
Tank
N
º
o
f
c
a
l
s
Meas
ured
by
exter
nal
labs
Used
from
Used
until
CH4
[ppb]
09.01.2013
06.03.2013
1866.00
07.03.2013
25.03.2013
1997.90
CO2
[pp
m]
N2O
[ppb
]
PXS2006
84
artificial
alu
1
D860384
natural
alu
1
PXS1460
52
artificial
alu
1
26.03.2013
26.12.2013
1750.90
PXS2758
63
artificial
alu
2
27.12.2013
10.03.2014
1944.35
400.97
328.50
PXS2758
64
artificial
alu
2
11.03.2014
08.05.2014
1963.25
401.69
327.11
PXS2758
60
artificial
alu
2
09.05.2014
29.07.2014
1971.55
401.26
327.39
PXS2760
87
artificial
alu
2
30.07.2014
10.10.2014
1944.05
400.14
326.48
PXS2760
86
artificial
alu
2
11.10.2014
28.01.2015
1950.05
398.63
326.21
PXS2760
82
artificial
alu
1
29.01.2015
30.03.2015
1950.05
400.54
349.51
PXS2760
80
artificial
alu
2
31.03.2015
10.08.2015
1948.35
401.75
326.13
PXS1074
03
artificial
alu
1
11.08.2015
1968.21
403.41
337.42
CH4
[ppb]
CO2
[pp
m]
N2O
[ppb
]
MPI Jena
318.00
414.59
327.98
308.36
Second working tank
Worki
ng
tank
ID
Filling
Tank
N
º
o
f
c
a
l
s
Meas
ured
by
exter
nal
labs
Used
from
Used
until
PXE2131
80
artificial
alu
1
15.02.2013
06.03.2013
388.19
PXE2380
64
artificial
alu
1
10.04.2013
26.12.2013
394.07
Table 3. Changes and parameters of response function standards (RFS).
3
Response function tanks
Respons
e
function
standar
ds ID
Filling
Tan
k
Nº
of
cal
s
Measur
ed by
externa
l labs
Used
from
Used
until
D860381
natural
alu
1
MPI Jena
09.01.2013
D860382
natural
alu
1
MPI Jena
09.01.2013
D860383
natural
alu
1
MPI Jena
D860384
natural
alu
1
D860385
natural
alu
D860386
natural
D860387
CH4
[ppb]
CO2
[pp
m]
N2O
[ppb
]
1698.4
369.98
309.48
25.03.2013
1796.8
385.12
318.15
09.01.2013
29.07.2014
1902.2
399.44
321.82
MPI Jena
25.03.2013
10.10.2014
1997.9
414.59
327.98
1
MPI Jena
09.01.2013
2098.0
429.96
332.04
alu
1
MPI Jena
09.01.2013
25.03.2013
2295.0
449.82
336.06
natural
alu
1
MPI Jena
09.01.2013
15.02.2013
2478.8
507.93
343.42
PXS283641
artificial
alu
1
26.11.2014
1849.9
395.67
321.93
PXS259614
artificial
alu
1
26.11.2014
2442.6
440.09
341.07
3. Nonlinearities and cross‐sensitivities
Nonlinearities and cross-sensitivities have not been checked.
4. Calibration strategy
Our measurements strategy can be summarized as shown here:
[…] - [RF determination]
determination] b – […]
a
- WT
i-1
– Sample
i
- WT
As an example, the calibrated mole‐fractions of Sample
derived according to the following procedure:
i
i+1
– etc. - [RF
(or Target i) are
Peak area ratios (both for CH 4 and N2O before 18/07/2014) are calculated
according to the following equation. After 18/07/2014 peak height is
considered for N2O ratios and peak area is still considered for CH 4.
Ratio
sample/RFS/target i
=A
sample/RFS/target i
/ mean(A
,A
WT i-1
WT i+1
)
Here the subindex “i” refers to a given run; so “i-1” refers to the preceding
one and “i+1” to the next one. Sample, response function standards (RFS)
and Target runs are included here together because the same ratio
computation is applied for each one.
4
RF determination is performed, in general, using several standards (see
Table 3) and making 6 replicates of each standard per RF.
The ratios of all RFS corresponding to the RF determination performed
before the run of interest (here [RF determination]a) are computed. The
same is done for the ratios of all RFS corresponding to [RF determination]b.
Then, since the concentrations of RFS represent the known variable, a linear
regression is applied considering concentrations as x-values and ratios as yvalues.
Ratio
RFS
= a Concentration
RFS
+b
Coefficients a and b are then used to derive concentration values
considering both RF determinations performed in between the run of
interest:
[Concentration
sample i a
] = (Ratio
sample i
– ba) / aa
[Concentration
sample i b
] = (Ratio
sample i
– bb) / ab
A weighted mean is then calculated considering the difference in time
between the run of interest and each RF determination:
[Concentration
i]b
sample i
] = α [Concentration
] + (1-α) [Concentration
sample i a
sample
where α represents the weight coefficient.
5. Internal Quality Assurance
For each species the target measurements are compiled in a uniform
manner (Figures 1-2). Since the mole fractions of the individual target
cylinders differ from each other, the deviation from the mean mole fraction
of each cylinder is shown. The graphs contain ambient air measurements as
well (upper panel of the Figures). In addition to this, the graphs highlight
changes of working standards and targets and provide a rough indication of
the target gas concentrations.
5
Figure 1 Methane ambient air measurements and target gas deviations
from the mean value. Blue lines represent WT changes; red lines
represent Target changes.
6
Figure 2. Nitrous Oxide ambient air measurements and target gas
deviations from the mean value. Blue lines represent WT changes; red
lines represent Target changes.
6. Intercomparison activities
Cucumbers tanks were measured at DEC station between the 20 th and the
25th of November 2014. Gases concentrations in Cucumbers tanks were
measured twice using a set of six NOAA tanks.
Table 4. Results of the cucumbers measurements performed in November
2014.
Results of the measurements done on 20/11/2014
Cucumber
tank ID
CH4
[ppb]
Std Dev
CH4
CO2
[ppm]
Std Dev
CO2
N2O
[ppb]
Std Dev
N2O
88478 (LOW)
1925.06
5.57
356.36
0.10
332.52
0.15
88484 (MED)
1884.25
1.88
379.87
0.05
319.83
0.19
88480 (HIGH)
2049.16
2.13
408.87
0.13
351.67
0.34
Results of the measurements done on 25/11/2014
7
Cucumber
tank ID
CH4
[ppb]
Std Dev
CH4
CO2
[ppm]
Std Dev
CO2
N2O
[ppb]
Std Dev
N2O
88478 (LOW)
1923.93
2.98
356.39
0.09
332.35
0.17
88484 (MED)
1886.81
0.56
379.91
0.06
320.43
0.26
88480 (HIGH)
2048.57
2.46
408.88
0.05
351.64
0.36
8