SAG-RG CO measurement techniques WCC-Empa audits

Transcription

1 Federal Office of Meteorology and Climatology MeteoSwiss Materials Sci ence & Technolog y SAG-RG CO measurement techniques WCC-Empa audits Christoph Zellweger, Brigitte Buchmann, Martin Steinbacher, Lukas Emmenegger Empa, Laboratory for Air Pollution/Environmental Technology, Duebendorf, Switzerland

2 International GAW Activities of Switzerland WCC-Empa (O 3, CO, CH 4, CO 2 ) QA/SAC Switzerland PMOD/WRC Davos GAWSIS Support to Ozonsounding Nairobi, Kenya Audits by WCC-Empa from Support to GAW Global Stations Mt. Kenya, Algeria, Indonesia Support to GCOS Cooperation Mechanism 2

3 Achievements of the WMO/GAW QA approach Audits by World Calibration Centres (WCCs) assess / ensure traceability to the CCL. Audits by WCC-Empa from In the case of surface ozone, WCC- Empa and the CCL (NIST) are both linked to BIPM through CCQM-K1. This QA approach leads to improved data quality; below are to statements from recent scientific publications: David Parrish Atmos. Chem. Phys., 12, , 2012 It should be noted that data quality has continuously improved over the decades of measurements due to steadily improving quality assurance procedures, e.g. systematic audits instituted by the GAW network in the early 1990s. Jennifer A. Logan JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, D09301, 2012 The data are most coherent since 1998 The GAW stations have been audited regularly since 1996 by the World Calibration Centre for Surface Ozone, Carbon Monoxide, Methane and Carbon Dioxide, hosted by Swiss Federal Laboratories for Materials Science and Technology (Empa). The audit process in place for the GAW stations had clearly improved the consistency of the alpine records. 3

4 Parallel measurements during WCC-Empa audits Why? Normal performance audits with travelling standards are a snapshot. They are usually made with operators present at the site (more careful calibration etc.). They usually do not assess the whole system including air inlet and air drying. How? Picarro G2401 travelling instrument with independent calibration and inlet system. If possible, the travelling analyzer is connected to both the station inlet and the completely independent WCC-Empa inlet. Duration of comparison usually 1-2 months. Next campaign will start next week at the Anmyeon-do GAW station. What? CO, CO 2, CH 4 (but no ozone). 4

5 Very successful implementation for CO 2 and CH 4 Example: CO 2, LoFlo Mark DMV 1-min No offset but large variability of the difference between instruments. Relatively high temporal variation, timing (residence time, clock adjustment etc.) and instrument response time is critical. 5

6 Example: CO 2, LoFlo Mark DMV 1-h matched If only 1-min TI with matching LoFlow data are considered for hourly averages, the agreement becomes much better. Data coverage is a issue, especially for sites with high ambient variability. 6

7 Carbon Monoxide: H 2 O interference? Pallas Example CO measurements with two Picarros G2401 (FMI: dry; WCC-Empa: humid) (Apr June 2012) at PAL :04 to :01 Picarro G2401 CFKADS-2018 Performance audit (comparison of dry travelling standards) showed good results within WMO/GAW DQOs. However, the ambient air comparison showed an offset of about 6 ppb between the two instruments. A clear dependency between the offset and the H 2 O content of the ambient air was found. [CO - <WMO-2004>] [ppb] Conclusion: Picarro implemented water vapor correction is not appropriate for humid CO measurements, at least for our travelling instrument (Serial#1) at the time of the audit <WMO-2004> [ppb] CO [ppb] CO (PAL-WCC) [ppb] WCC-Empa TI WCC Inlet WCC-Empa TI PAL Inlet PAL Picarro G2401 WMO/GAW DQOs CO(PAL) - CO(WCC) [ppb] Frequency (counts) Picarro G2401 Mean (ppb) Median (ppb) St.dev (ppb) H2O [%] Deviation to WCC-Empa [ppb] 7

8 CO: Comparison with Nafion dryer Cape Verde WCC-Empa: Picarro G2401 with Nafion dryer. CVO: LGR-23r with dryer (cold trap). Performance audit results are within the DQOs, negative bias at 100 ppb CO. Ambient air comparison results are also mostly within the DQOs, but positive bias at 100 ppb CO. Bias shows a strong diurnal variation, which is most likely due to the Picarro measurements. [CO - <WMO-2004>] [ppb] :12 to :08 LGR 23-d CVO <WMO-2004> [ppb] CO [ppb] Bias [ppb] Picarro G2401 WCC Los Gatos LGR-23d MPI-BGC Frequency (counts) Los Gatos LGR-23d MPI-BGC Mean (ppb) Median (ppb) St.dev (ppb) Deviation to WCC-Empa [ppb] 8

9 New campaign (humid): MHD Mace Head WCC-Empa: Picarro G2401 (SN #98) without drying system; correction to dry air mole fraction applied by internal correction function of Picarro. MHD: RGA-3 (dry air mole fractions). Performance audit results were considered to correct for CO bias. Resulting ambient air comparison results are mostly within the DQOs. New instrument: no relationship between CO bias and H 2 O. CO [ppb] CO (MHD-WCC) [ppb] Picarro G2401 WCC RGA-3 MHD corrected based on TS comparison (eq. 2a) CO(MHD) - CO(WCC) [ppb] [CO - <WMO-2004>] 0 (ppb) 5 10 Frequency (counts) :12 to : <WMO-2004> 1.6 (ppb) 2.0 RGA-3 MHD Mean (ppb) Median (ppb) St.dev (ppb) H2O [%] Deviation to WCC-Empa [ppb] (all data) RGA3 9

10 New campaign (humid): IZO Izaña WCC-Empa: Picarro G2401 (SN #1, after upgrade of correction function) without drying system; correction to dry air mole fraction applied by internal correction function of Picarro. IZO: RGA-3 (dry air mole fractions). Small difference between performance audit results and ambient air measurements. SN #1instrument after upgrade: no relationship between CO bias and H 2 O. CO(IZO) - CO(WCC) [ppb] [CO - <WMO-2004>] 0 (ppb) :11 to :41 RGA <WMO-2004> 1.0 (ppb) 1.5 H2O [%] CO [ppb] CO (IZO-WCC) [ppb] Picarro G2401 WCC Inlet Picarro G2401 IZO Inlet RGA-3 IZO WMO/GAW DQOs Frequency (counts) RGA-3 IZO Mean (ppb) Median (ppb) St.dev (ppb) Deviation to WCC-Empa [ppb] (all data) 10

11 CO measurement techniques NDIR Non Dispersive Infrared Absorption GC-HgO Gas Chromatography with HgO Detector GC-FID Gas Chromatography with FID Detector VURF Vacuum UV Resonance Fluorescence CRDS Cavity Ring Down Spectroscopy (near IR) QCL Quantum Cascade Laser Spectroscopy (mid IR) ICOS QCL cavity enhanced off-axis Integrated Cavity Output Spectroscopy (mid IR) 11

12 Performance of CO measurement techniques Results published in two papers: NDIR, VURF, GC-HgO, GC-FID Zellweger, C., Hüglin, C., Klausen, J., Steinbacher, M., Vollmer, M., and Buchmann, B.: Intercomparison of four different carbon monoxide measurement techniques and evaluation of the long-term carbon monoxide time series of Jungfraujoch, Atmos. Chem. Phys., 9, , VURF, CRDS, Two QCL instruments (LGR, Aerodyne) Zellweger, C., Steinbacher, M., and Buchmann, B.: Evaluation of new laser spectrometer techniques for in-situ carbon monoxide measurements, Atmos. Meas. Tech., 5, , /amt , Summary of results were presented at last SAR-RG meeting 12

13 New since last meeting: Picarro G CO Improved stability and precision of Picarro G2401 model. 1-σ standard deviation decreased from ppb to 5-6 ppb (5 sec data). One standard gas was continuously measured for almost 20 days. No significant drift of the standard, confirmed by calibration against reference standards. No significant instrument drift. Optimal calibration interval ~10h, but 30h or even longer is enough to reach compatibility goals. Min avgeraging time ~5 min 13

14 New since last meeting: Picarro G CO Improved water vapor interference correction of Picarro G2401 model. Results of laboratory experiments and parallel measurements during audits now show that the water vapor correction of the Picarro CRDS instrument is now also appropriate for CO. Laboratory experiment Field: Mace Head Field: Izaña CO(MHD) - CO(WCC) [ppb] CO(IZO) - CO(WCC) [ppb] H2O [%] H2O [%] 14

15 Summary Improved stability and precision of Picarro G2401 model. 100 rough, qualitative sketch More recent techniques (CRDS, QCL) have better performance compared to GC and NDIR. VURF still good but technique has no future due to need of expensive auxiliary gases and frequent calibration. Precision (ppb) Time (s) Values are estimates and can vary depending on instrument 15

16 Conclusions Parallel measurements during audits are an independent check that includes the whole measurement system (inlet, instrumentation, air pretreatment, analysis, calibration, data processing). provide additional information which can only be partly achieved with round robins comparisons or travelling standard. gives additional information on the uncertainty of a time series. help to identify problems with a measurement set-up. include an assessment of the influence of sample drying We could show that sample drying is not needed for CO with improved correction algorithm implemented in the more recent CRDS instruments. the performance of the CRDS instrument improved significantly. data coverage is an important aspect with respect to the uncertainty of measurement data. Outlook WCC-Empa will continue using travelling instruments during on-site audits whenever it is feasible. Further compare data series with perfect agreement between WCC-Empa and station measurements with other available data (e.g. flasks). 16

17 Thank you! Acknowledgements: IZO: Angel Gomez, Emilio Cuevas CVO: Ally Lewis, Katie Read MHD: Gerry Spain NOAA/GMD: Paul Novelli 17