Long-term field intercomparison of N 2 O observations with GC-ECD and Cavity Enhanced Absorption Spectroscopy at Jungfraujoch

Transcription

1 Long-term field intercomparison of N 2 O observations with GC-ECD and Cavity Enhanced Absorption Spectroscopy at Jungfraujoch Martin Steinbacher, Christoph Zellweger, Lukas Emmenegger, Brigitte Buchmann Empa, Laboratory for Air Pollution / Environmental Technology, Duebendorf, Switzerland 17 th WMO/IAEA Meeting on Carbon Dioxide, Other Greenhouse Gases, and Related Measurement Techniques (GGMT-2013), Beijing, June 2013

2 Jungfraujoch (JFJ) 3580 m asl, 7 59' E, 46 32' N part of the Swiss National Air Monitoring Pollution Network one of the 29 Global GAW sites well suited for monitoring the free troposphere source allocations in Central Europe Laboratory for Air Pollution/Environmental Technology # 2

3 Nitrous Oxide JFJ GC-ECD Agilent 6890N with FID (CH 4, CO) and ECD (N 2 O, SF 6 ) detector since February 2005 length of run: 12min each ambient air sample is bracketed with calibration runs standards are traced back to SIO-98 (till April 2012) and NOAA-2006A (after April 2012) scale target gas measurements three times a week (3 subsequent analysis) samples are dried with a Nafion dryer precision based on recurrent working standard analyses: ~ 0.07% for N 2 O Laboratory for Air Pollution/Environmental Technology # 3

4 N2O time series at Jungfraujoch trend ( ): 1.0 ppb yr -1 Laboratory for Air Pollution/Environmental Technology # 4

5 N2O [ppb] N2O [ppb] N2O time series at Jungfraujoch hourly mean daily mean Jungfraujoch Jul 04 Jul 09 Jul 14 Jul 19 Jul 24 Jul 29 time [mmm dd] in 2012 JFJ, mean seasonal cycle, observation of distinct events is rare a seasonal cycle can be seen when considering all data J F M A M J J A S O N D Month Laboratory for Air Pollution/Environmental Technology # 5

6 LGR-23r N2O/CO with enhanced performance analysis based on off-axis integrated cavity output spectroscopy detection in the mid-ir using a quantum-cascade laser 42 cm (width) x 50 cm (height) x 80 cm (depth), 70kg enhanced performance, i.e. active temperature stabilization model N 2 O/CO-23r with enhanced performance configuration model N 2 O/CO-23d Laboratory for Air Pollution/Environmental Technology # 6

7 N2O [ppb] Los Gatos LGR-23r N2O/CO monitor LGR-23r (1Hz data) mean median st.dev N LGR-23r (1min av.) mean median st.dev N Time since start (s) N 2 O precision: 0.11 ppb for 1 Hz 0.02 ppb for 1-min data) for comparison: results of 12 injections of a reference gas, measured with GC-ECD (required time ~ 4 ½ h) Laboratory for Air Pollution/Environmental Technology # 7

8 N2O - Allan Standard Deviation (ppb) Allan Variance Plot N2O/CO 23r EP 1e+00 1e+01 1e+02 1e+03 Cluster Time (s) Laboratory for Air Pollution/Environmental Technology # 8

9 N2O - Allan Standard Deviation (ppb) N2O - Allan Standard Deviation (ppb) Allan Variance Plot LGR-23d N2O/CO 23d N2O/CO 23r EP 1e+00 1e+01 1e+02 1e+03 Cluster Times (Sec) achieved precisions: 1e+00 1e+01 1e+02 1e+03 Cluster Time (s) precision [ppb] averaging time [min] ~ ~ EP version is slightly superior compared to version w/o enhanced performance Laboratory for Air Pollution/Environmental Technology # 9

10 LGR-23r at Jungfraujoch Laboratory for Air Pollution/Environmental Technology # 10

11 MIU before and after modification inlet ports 9-16 out (to analyzer) inlet ports 1-8 bulkhead union solenoid (on/off) valve Multi Inlet Union Disadvantages: no overflow option, teflon tubing and teflon bulkhead unions, dead volumes Laboratory for Air Pollution/Environmental Technology # 11

12 MIU before and after modification overflow out inlet ports 1-8 (to analyzer) bulkhead union solenoid (on/off) valve N.O. Multi Inlet Union Disadvantages: no overflow option, teflon tubing and teflon bulkhead unions, dead volumes Modifications: additional solenoid valve to allow measuring pressurized air under ambient pressure conditions, dekabon tubing, stainless steel bulkhead unions, use of only 8 ports Laboratory for Air Pollution/Environmental Technology # 12

13 MIU after modification flows for each port can be individually set with needle valves Laboratory for Air Pollution/Environmental Technology # 13

14 N2O target, calibrated [ppb] N2O cal2, raw [ppb] N2O cal3, raw [ppb] N2O cal4, raw [ppb] Calibration results March till mid-april 2013 nominal value mean of measured values 3/2 3/5 3/8 3/12 3/16 3/20 3/24 3/28 4/1 4/4 4/7 date [mm/dd] 3 calibration gases every 47 hours, one target cylinder every 15 hours Laboratory for Air Pollution/Environmental Technology # 14

15 N2O [ppb] Calibration results, cont d several sudden significant sensitivity losses, accompanied by huge H 2 O signals target tank, calibrated data Jan 2013 Feb 2013 Mar 2013 Apr 2013 May 2013 Jun 2013 date [mmm yyyy] Laboratory for Air Pollution/Environmental Technology # 15

16 N2O [ppb] Ambient air data N2O, hourly averages i.e. average of 2 to 3 discrete injections (ECD) and full coverage hourly averages (LGR) hourly data LGR GC-ECD 2/20 2/23 2/26 3/1 3/4 3/7 3/10 3/13 3/16 3/19 3/22 3/25 3/28 3/31 4/3 4/6 4/9 date [mm/dd] small bias (cross-calibration of the calibration gases is still pending) short-term structure seen with LGR isn t always resolved with ECD Laboratory for Air Pollution/Environmental Technology # 16

17 delta CO [ppb] CO [ppb] Ambient air data CO comparison of LGR s CO data with other available CO record at Jungferaujoch LGR CDRS 2/20 2/23 2/26 3/1 3/4 3/7 3/10 3/13 3/16 3/19 3/22 3/25 3/28 3/31 4/3 4/6 4/9 date [mm/dd] rather good agreement, all features are recorded with both techniques Laboratory for Air Pollution/Environmental Technology # 17

18 Ambient are data N2O, CH4 & CO does the N 2 O variability correlate with variations of other trace gases? some events are seen in all trace gases while others (especially with low N 2 O) are not reflected in the CH 4 and CO data record Laboratory for Air Pollution/Environmental Technology # 18

19 Conclusions laboratory tests of the off-axis ICOS from LGR showed very satisfactory and promising results modifications were required to use the LGR Multi Inlet Unit according to our needs in the field, calibrations every 2 days revealed the need for frequent sensitivity checks severe sensitivity losses were observed 3 times in 6 months, always accompanied with events of very high H 2 O readings agreement for N 2 O with GC-ECD is poor agreement for CO with another laser spectrometer is satisfactory comparison of the N 2 O, CH 4 and CO time series at Jungfraujoch identifies some common features the origin of some patterns in the N 2 O record measured with the LGR analyzer (atmospheric variability, artifacts?) are subject to further investigations Laboratory for Air Pollution/Environmental Technology # 19

20 Acknowledgements Swiss Federal Office for the Environment MeteoSwiss International Foundation High Altitude Research Stations Jungfraujoch and Gornergrat Thank you for your attention! Laboratory for Air Pollution/Environmental Technology # 20