Comparison of different CO2 measurement techniques at the ...

Comparison of different CO2 measurement techniques at the Schauinsland station Frank Meinhardt Federal Environmental Agency

GHG-Europe Workshop Heidelberg 22.11. – 24.11.2010

Umweltbundesamt

Ambient CO2 Mixing ratios at Schauinsland from 1972 to 2010 July 2000 and applied technics July 1991 Setup of a 410CO2 [ppm] 400 390 380 370 360 350 340 330 320 310

NDIR Technics only. Usage of Unor, Ultramat, Instruments

additional Setup of a Siemens Sichromat GC system

HP (Agilent) GC system

2008 Start of Loflo Ambient measurements

1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Annual variation

daily means


Umweltbundesamt

First facilities for ambient CO2 measurements

Setup of the first CO2 NDIR Measurement system in the end of the sixies. Due to problems with the Carrier gas effect and a lack of reliable, stable working standards, usable datas not before 1972.


Umweltbundesamt

CO2 Comparison of Uras 3E and Siemens Sichromat GC 1993 – 1999 Δ(GC – NDIR) on daily mean time base (unselected) 6

Period from 6.94 to 6.97 Mean: 0.07 ppm Stand.-dev: 0.7 ppm

delta Conc CO2 ppm

4

2

0

-2

-4

6.94 Start using a compressor cooler

-6 3.1.92

2.1.93

2.1.94

2.1.95

2.1.96

1.1.97

1.1.98

1.1.99

1.1.00

31.12.00

Date Delta Siemens GC - Uras NDIR


Umweltbundesamt

HP (Agilent) 6890 GC system at Schauinsland

Normal ambient cycle: Two ambient and one Standard measurement. Max 6 ambient measurements per hour (less by conducting additional tank measurements) Target gas measurements Once a day

Components: CO2, CH4, N2O, SF6 H2 and CO GHG-Europe Workshop Heidelberg 22.11. – 24.11.2010

Umweltbundesamt

CO2 Comparison of Uras 3E and HP GC 2001 – 2007 Δ(GC – NDIR) on daily mean time base (unselected) Mean: 0.05 ppm Standarddeviation: 0.8 ppm

6

Delta CO2 ppm

4

2

0

-2

-4

-6 06.12.1999

19.04.2001

01.09.2002

14.01.2004

28.05.2005

10.10.2006

22.02.2008

06.07.2009

Date

HP GC - Uras NDIR


Umweltbundesamt

How do the variation of the CO2 signal influence on the consistence of the signals? • Due to the different technics (only 4 to 6 single spot values per hour with the GC instrument versus real mean values with the NDIR instrument), the deviation of the results may depend with the variation of the CO2 concentration. • This should be visible by applying a data selection. (Selection rules: only nighttime datas from 22:00 to 6:00 MEZ, windspeed > 2.5m/s in summer/ 3.5m/s in winter, Stand. Deviation < 1 ppm for halfhour mean values)


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CO2 Comparison of Uras 3E and HP GC 2000 – 2007 selected versus unselected data 6

Delta CO2 ppm

4

Unselected data: mean 0.05 ppm Stand. Dev. 0.8 ppm Selected data: mean 0.06 ppm Stand. Dev 0.8 ppm

2

0

-2

-4

-6 06.12.1999 19.04.2001 01.09.2002 14.01.2004 28.05.2005 10.10.2006 22.02.2008 06.07.2009 Date

HP GC - Uras NDIR

(GC - URAS) selected data


Umweltbundesamt

Loflo NDIR instrument from CSIRO (based on a Licor module) Improved precision: Repeatability of tank measurings ~ 0.02 ppm. Drying of ambient air down to Dp< -60 C with a nafion dryer.


Umweltbundesamt

Conc CO2 ppm

CO2 Comparison of Uras 3E, HP GC, Loflo NDIR and Picarro instrument. 15.7.2008 hourly means GC korr(1) Uras korr(2) Loflo(3) Picarro(4)

378 375 372

Delta CO2 ppm

2 1 0 -1

Loflo - GC mean -0.045 ppm, std.dev. 0.26 ppm Loflo - Uras mean 0.78 ppm, std.dev. 0.18 ppm Loflo - Picarro mean 0.22 pp, std.dev. 0.7 ppm

-2 24:00

04:00

08:00

12:00 Time

16:00

20:00

24:00

CO2 Comparison of Uras 3E, HP GC and Loflo NDIR instrument 2009 daily means Uras

4

Delta Loflo-Uras

CO2 [ppm]

Uras 2

mean: 0.10 ppm std.: 1.24 ppm

0 -2 4

Delta Loflo-GC

CO2 [ppm]

GC

GC

2

mean: 0.04 ppm std.: 0.92 ppm

0 -2

Jan

Mrz

Mai

Jul Date

Sep


Nov

Jan Umweltbundesamt

Conclusion • Under the present measurement conditions at Schauinsland station a deviation between the long term NDIR and GC CO2 records of < 0.1 ppm with a standard deviation of < 1 ppm is realistic for daily means. • In order to detect all kind of problems with a measurement system, a second independent instrument is very useful.


Umweltbundesamt

Outlook • A new station building at Schauinsland will likely be constucted in the next two years. So we will definitely get a better climatisation. • A taller inlet system > 35m is planned. • This year the Uras NDIR instrument will be replaced by a picarro instument.


Umweltbundesamt