Markus Leuenberger1, Tesfaye Berhanu1, Peter Nyfeler1, David Kim-Hak2, John Hoffnagle2 and Minghua Sun2. Bern, Switzerland

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1 GGMT-2017, Dübendorf, Switzerland August 30, 2017 Measurements of atmospheric oxygen using a newly built CRDS analyzer and comparison with a paramagnetic and an IRMS. Markus Leuenberger1, Tesfaye Berhanu1, Peter Nyfeler1, David Kim-Hak2, John Hoffnagle2 and Minghua Sun2 1Climate and Environmental Physics Institute, University of Bern, Bern, Switzerland 2Picarro Inc., Santa Clara, USA

2 GGMT-2017 in Dübendorf, Switzerland Interaction of the carbon and the oxygen cycle through biogeochemical processes 29 August

3 CRDS: time, not absorbance CRDS utilizes the unique infrared absorption spectrum of gas-phase molecules to quantify the concentration of (and sometimes isotopes of) H 2 O, CO 2, CH 4, N 2 O, CH 2 O, NH 3, etc. Measure decay rate, rather than absolute absorbance Small 3-mirrored cavity ~ 35 cc Long effective path-length (> 10 km) Time-based measurement Laser is switched on and off, and scanned across wavelengths

4 CRDS principle of operation laser detector signal WLM D tune laser to target l L Nl L = Nl D D cavity not resonant cavity resonant time (microseconds) D laser OFF for Ring Down measurement repeat process every 3 msec

5 CRDS: Cavity Ring-Down Spectroscopy Measure decay time using CRDS Detector Signal Select wavelength using λ-monitor t I circ (t ) I circ (to ) exp Time Calculate absorbance a = 1/c ringdown c: Speed of light a : Loss per unit length

6 Analyzer: G2207-i (NEW) G2207-i Features: - Cavity Ring Down Spectroscopy (CRDS) Technology - Measure simultaneously [O 2 ] and [H 2 O] - 1 PPM level of precision for [O 2 ] Absorption Spectroscopy: - Oxygen absorption line: cm -1 - H2O absorption line: 7817 cm -1 - P = 255 torr and T = 45 C

7 Water Correction We always pay special attention to water vapor Highly variable in ambient air Sticky therefore slow to disappear from ring-down cavity that has been exposed to moisture Measured with second laser tuned to absorption line at 7817 cm-1 45 ring-downs devoted to water add some overhead to oxygen measurement Precision better than 1 ppm Characterized cross-broadening and dilution of oxygen by water vapor Still need to dry samples for best O 2 accuracy

8 Specifications

9 Allan Variance Plot Allan standard deviation reaches 1 ppm (or 5 per meg) after 200 s based on 1-week measurement from cylinder of dry zero-air Picarro Inc.

10 Evaluation at University of Bern Objectives: Compare Picarro G-2207 (, H2O) versus Paramagnetic sensor () and Mass Spectrometer (δ/n2) Evaluate H2O measurement and correction IRMS 2016 Picarro Inc.

11 GGMT-2017 in Dübendorf, Switzerland Measurements of eight standard gases 10

12 GGMT-2017 in Dübendorf, Switzerland Measurements of eight standard gases High C value 11

13 Correlation of Standard Gas Measurements Extended range MS-δ/N2 (per meg) MS-δ/N2 (per meg) Restricted range 800 y = x - 1E+06 R² = y = x - 1E+06 R² = Picarro (ppm) y = x R² = Picarro Inc. Picarro (ppm) y = 1.52x R² = Paramagnetic () Paramagnetic ()

14 Correlation of Standard Gas Measurements Extended range MS-δ/N2 (per meg) MS-δ/N2 (per meg) Restricted range 800 y = x - 1E+06 R² = y = x - 1E+06 R² = Picarro (ppm) y = x R² = Picarro Inc. Picarro (ppm) y = 1.52x R² = Paramagnetic () Paramagnetic ()

15 GGMT-2017 in Dübendorf, Switzerland Characterization of standards used Picarro Picarro Licor Licor Licor Licor Para-Bern Para-Bern MS MS MS F (1-min) stdev F (1-min) Stdev F (1-min) Stdev F (1-min) Stdev F F F Gas H2O H2O C C H2O d/n2 dar/n2 C ST1 to ST8/units ppm ppm ppm ppm ppm ppm non-calib H2O noncalib non-calib non-calib ppm Ref 2 (LUX3576) Ref 1( LK922131) CA07045_Scripps CA07043_Scripps CA07047_Scripps CA04556_NOAA CA06943_NOAA LK Table 1: Measurements of eight standard cylinders with three different measurement techniques (Picarro-CRDS, Para-Bern and Mass Spectrometry) 29 August

16 GGMT-2017 in Dübendorf, Switzerland Calibrated values based on MS Picarro F (1Gas min) Name/units ppm Ref 2 (LUX3576) ParaBern on Picarro Picarro on MS Picarro on MS dil cor Picarro on MS dil cor ex H2O Para-Bern ParaBern on MS F (1- F (1-min) Cal # ParaBern on MS dil cor Para-Bern on MS dil cor ex H2O MS MS Dil cor F Dil cor d/n2 Dil cor ex H2O MS /N2 d d /N2 min) ppm non-calib Ref 1( LK922131) CA07045_Scripps CA07043_Scripps CA07047_Scripps CA04556_NOAA CA06943_NOAA N/A N/A N/A LK Table 2: Comparison of Picarro and Para-Bern measurements calibrated with /N2 measurements on the Bern mass spectrometer as displayed in Fig. 11 and 12. #: The calibration was done using the correlation with ST-1 to ST6. 29 August

17 GGMT-2017 in Dübendorf, Switzerland Differences among techniques used Diff MS-Picarro Diff MS-Picarro Diff MS-Picarro Diff MS-Para Diff MS-Para Diff MS-Para Diff Para-Picarro Diff Para-Picarro Diff Para-Picarro F Dil cor Dil cor ex H2O F Dil cor Dil cor ex H2O F Dil cor Dil cor ex H2O Gas d/n2 d/n2 d/n2 Name/units Ref 2 (LUX3576) Ref 1( LK922131) CA07045_Scripps CA07043_Scripps CA07047_Scripps CA04556_NOAA CA06943_NOAA LK August

18 GGMT-2017 in Dübendorf, Switzerland Tests at Bern University 29 August

19 GGMT-2017 in Dübendorf, Switzerland Drifting trend in the Picarro for the two standard gases 29 August

20 GGMT-2017 in Dübendorf, Switzerland Correction for the drift 29 August

21 GGMT-2017 in Dübendorf, Switzerland Dried outside air measurements for both instruments after calibration with ST1 and ST2 A standard deviation of 1-2 ppm for the Reference gases! 29 August

22 Water Measurement Comparison H2O Comparison: Licor vs Picarro G2207-i Para-Bern 5 Picarro Days after January 1, Picarro Inc Picarro G2207 [ppm] H2O Licor [mmol/mol] H2O

23 Non-Dried Sample Analysis with H2O Correction 2016 Picarro Inc.

24 Beromunster Tower Experiment 5 sampling inlets (12 m 212 m) Permanent Picarro G-2401 analyzer for CH4, C, CO, H2O measurements. Objective: - Height dependence of changes in C and 2016 Picarro Inc.

25 and C Concentrations at 212 and 12m : C with G2401 Concentration (ppm) : with G2207-i 30 s values C in blue in green Concentration (ppm) lines 5 min running means over the course of a day 2016 Picarro Inc.

26 Concentration (ppm) /C Correlation at 212 and 12m Slope ppm / ppm C r2 = 0.64 C Concentration (ppm) Concentration (ppm) Slope ppm / ppm C r2 = 0.49 C Concentration (ppm) 2016 Picarro Inc.

27 GGMT-2017 in Dübendorf, Switzerland Conclusion > Precision of the instrument measured with standards agree with the value derived from the Allan plot, i.e 1 ppm (5 5 minutes. > Advantages are (i) a less frequent required instrument calibration; (ii) easy to install and use instrument and (iii) data handling is rather simple. > Disadvantages are (i) the long-term drift (seems to be solved by Picarro); (ii) the non availability of concurrent CO 2 measurements; (iii) therefore no implemented CO 2 dilution nor Ar dilution effect and (iv) the prize. > It is easy field employable, most probably usable on moving platforms such as ships and airplanes. > Points to be improved: water correction, in particular in low H 2 O range, O 2 concentration precision in the isotope mode, interferences on O 2 isotopes 29 August