Title page 1

Contents 5

ACKNOWLEDGEMENTS 4

1. EXECUTIVE SUMMARY 6

2. SITE DESCRIPTION AND OPERATION 7

2.1. Station management 7

2.2. Location and access 7

2.3. Station facilities 7

3. MEASUREMENT PROGRAMME 8

4. DATA SUBMISSION 9

4.1. Data review 9

4.2. Documentation 9

4.3. Air inlet system 9

5. PERFORMANCE AUDIT 11

5.1. Surface ozone measurements 11

5.2. Carbon monoxide measurements 15

5.3. Methane measurements 17

5.4. Carbon dioxide measurements 20

5.5. Nitrous oxide measurements 22

6. COMPARISON OF CGO PERFORMANCE AUDIT RESULTS WITH OTHER STATIONS 26

7. PARALLEL MEASUREMENTS OF AMBIENT AIR 29

7.1. Carbon monoxide 29

7.2. Methane 29

7.3. Carbon dioxide 29

8. CONCLUSIONS 37

9. SUMMARY RANKING OF THE KENNAOOK/CAPE GRIM GAW STATION 39

APPENDIX 40

A1. List of recommendations 40

A2. Data review 41

A3. Surface ozone comparisons 52

A4. Carbon monoxide comparisons 61

A5. Methane comparisons 62

A6. Carbon dioxide comparisons 64

A7. Nitrous oxide comparisons 65

A8. WCC-Empa ozone travelling standard 67

A9. WCC-Empa GHG and CO travelling standards 70

A10. Calibration of the WCC-Empa travelling instrument 74

REFERENCES 77

LIST OF ABBREVIATIONS 78

Tables 37

Table 1. Summary of the performance audit and parallel measurement results at Kennaook / Cape Grim. A tick mark in the table indicates that... 37

Table 2. Experimental details of the ozone comparison 52

Table 3. Comparison of the main CGO ozone analyser (OA) Thermo Scientific 49i #CM16160046 (BKG -0.0 nmol mol⁻¹, COEF 0.984) with the bias corrected... 53

Table 4. Comparison of the CGO ozone analyser (OA) Thermo Scientific 49iQ #1191302833 (BKG +0.5 nmol mol⁻¹, COEF 0.978) with the bias corrected... 55

Table 5. Comparison of the CGO ozone analyser (OA) Thermo Scientific 49i-PS #1180930024 (BKG 0.0 nmol mol⁻¹, COEF 0.988) with the bias corrected... 57

Table 6. Comparison of the CGO ozone calibrator (OC) Thermo Scientific 49i-PS #1315588104 (BKG -0.4 nmol mol⁻¹, COEF 1.003) with the bias corrected... 59

Table 7. CO aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the Picarro... 61

Table 8. CO aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the CGO... 61

Table 9. CO aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the GASLAB... 62

Table 10. CH₄ aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the Picarro... 63

Table 11. CH₄ aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the CGO... 63

Table 12. CH₄ aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the GASLAB... 64

Table 13. CO₂ aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the Picarro... 64

Table 14. CO₂ aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the CSIRO... 65

Table 15. N₂O aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the Picarro... 66

Table 16. N₂O aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the CGO... 66

Table 17. N₂O aggregates calculated from individual analyses (mean and standard deviation of the mean) for each level during the comparison of the CSIRO... 67

Table 18. Mean values calculated over at least five minutes for the comparison of the WCC-Empa travelling standard (TS) with the Standard Reference Photometer (SRP) 68

Table 19. CCL laboratory standards and working standards at WCC-Empa 71

Table 20. Calibration summary of the WCC-Empa travelling standards for CH₄, CO₂, N₂O and CO. The letters in parenthesis refer to the instrument... 71

Figures 10

Figure 1. Schematic overview of the plumbing and inlet system for the CGO CRDS and GC-MD instruments 10

Figure 2. Left: Bias of the CGO ozone analyser (Thermo Scientific 49i #CM16160046, BKG -0.5 nmol mol⁻¹, COEF 0.984) with respect to the SRP... 12

Figure 3. Left: Bias of the CGO ozone analyser (Thermo Scientific 49iQ #1191302833, BKG +0.5 nmol mol⁻¹, COEF 0.978) with respect to the SRP... 12

Figure 4. Left: Bias of the CGO ozone calibrator (Thermo Scientific 49i-PS #1180930024, BKG 0.0 nmol mol⁻¹, COEF 0.988) with respect to the SRP... 14

Figure 5. Left: Bias of the CGO ozone calibrator (Thermo Scientific 49i-PS #1315588104, BKG 0.0 nmol mol⁻¹, COEF 1.003) with respect to the SRP... 14

Figure 6. Left: Bias of the PICARRO G5310 #5066-DAS-JKADS5075 carbon monoxide instrument with respect to the WMO-X2014A reference scale... 16

Figure 7. Left: Bias of the CGO GC-MD carbon monoxide instrument with respect to the WMO-X2014A reference scale as a function of the amount fraction.... 17

Figure 8. Left: Bias of the CSIRO GASLAB GC-RGD carbon monoxide instrument with respect to the WMO-X2014A reference scale as a function of the amount fraction.... 17

Figure 9. Left: Bias of the Picarro G2301 #1151-CFADS2263 instrument with respect to the WMO-X2004A CH₄ reference scale as a function of the amount fraction.... 18

Figure 10. Left: Bias of the CGO GC-MD instrument with respect to the WMO-X2004A CH₄ reference scale as a function of the amount fraction.... 19

Figure 11. Left: Bias of the CSIRO GASLAB GC-FID methane instrument with respect to the WMO-X2004A reference scale as a function of the amount fraction.... 20

Figure 12. Left: Bias of the Picarro G2301 #1151-CFADS2263 CO₂ instrument with respect to the WMO-X2019 reference scale as a function of the amount fraction.... 21

Figure 13. Left: Bias of the CSIRO GASLAB GC-FID instrument with respect to the WMO-X2019 reference scale as a function of the amount fraction.... 21

Figure 14. Left: Bias of the CGO Picarro G5310 #5066-DAS-JKADS5075 nitrous oxide instrument with respect to the WMO-X2006A reference scale... 23

Figure 15. Left: Bias of the CGO GC-MD nitrous oxide instrument with respect to the WMO-X2006A reference scale as a function of the amount fraction.... 23

Figure 16. Left: Bias of the CSIRO GASLAB GC-ECD nitrous oxide instrument with respect to the WMO-X2006A reference scale as a function of the amount fraction.... 25

Figure 17. O₃ bias in the middle of the relevant amount fraction range compared to the slope of the WCC-Empa performance audits. The grey dots correspond... 26

Figure 18. CO (top left), CH₄ (top right), CO₂ (bottom left) and N₂O (bottom right) bias in the middle of the relevant amount fraction range compared... 28

Figure 19. Top: Comparison of the Picarro G5310 #5066-DAS-JKADS5075 with the WCC-Empa travelling instrument for CO. Time series based on hourly data... 30

Figure 20. Top: Comparison of CGO GC-MD with the WCC-Empa travelling instrument for CO. Time series based on 1 min data (WCC-Empa)... 31

Figure 21. Top: Comparison of the G2301 #1151-CFADS2263 analyser (main instrument) with the WCC-Empa travelling instrument for CH₄.... 32

Figure 22. Top: Comparison of the G2301 #2121-CFADS2386 analyser (backup instrument) with the WCC-Empa travelling instrument for CH₄.... 33

Figure 23. Top: Comparison of CGO GC-MD with the WCC-Empa travelling instrument for CH₄. Time series based on 1 min data (WCC-Empa)... 34

Figure 24. Top: Comparison of the G2301 #1151-CFADS2263 analyser (main instrument) with the WCC-Empa travelling instrument for CO₂.... 35

Figure 25. Top: Comparison of the G2301 #2121-CFADS2386 analyser (backup instrument) with the WCC-Empa travelling instrument for CO₂.... 36

Figure 26. WDCRG O₃ data for the period 1981 to 2022. Top: Time series, hourly averages. Bottom: Left: frequency distribution, middle: diurnal variation,... 41

Figure 27. CGO in-situ CO data (GC-MD) (1993-2023) provided by AGAGE. All valid data are shown. Top: Time series, hourly averages.... 42

Figure 28. CGO CO flask data (1984-2023) submitted to WDCGG by CSIRO. Top: Time series, hourly averages. Bottom: Left: frequency distribution,... 42

Figure 29. CGO CO flask data (1990-2023) submitted to WDCGG by NOAA. Top: Time series, hourly averages. Bottom: Left: frequency distribution,... 43

Figure 30. CGO in-situ CH₄ data (GC-MD) (1981-1994) provided by AGAGE. All valid data are shown. Top: Time series, hourly averages.... 44

Figure 31. CGO in-situ CH₄ data (GC-MD) (1993-2023) provided by AGAGE. All valid data are shown. Top: Time series, hourly averages.... 44

Figure 32. CGO in-situ CH₄ data (Picarro) (2013-2023) provided by AGAGE. All valid data are shown. Top: Time series, 1 minute averages.... 45

Figure 33. CGO CH₄ flask data (1984-2023) submitted to WDCGG by CSIRO. Top: Time series, hourly averages. Bottom: Left: frequency distribution,... 45

Figure 34. CGO CH₄ flask data (1984-2023) submitted to WDCGG by NOAA. Top: Time series, hourly averages. Bottom: Left: frequency distribution,... 46

Figure 35. CGO in-situ CO₂ data (LoFlo Mk2 NDIR instrument) (2004-2019) provided by CSIRO. All valid data are shown. Top: Time series, hourly averages.... 47

Figure 36. CGO CO₂ flask data (1984-2023) submitted to WDCGG by CSIRO. Top: Time series, hourly averages. Bottom: Left: frequency distribution,... 47

Figure 37. CGO CO₂ flask data (1990-2023) submitted to WDCGG by NOAA. Top: Time series, hourly averages. Bottom: Left: frequency distribution,... 48

Figure 38. CGO in-situ N₂O data (GC-MD) (1978-1985) provided by AGAGE. All valid data are shown. Top: Time series, hourly averages.... 49

Figure 39. CGO in-situ N₂O data (GC-MD) (1981-1994) provided by AGAGE. All valid data are shown. Top: Time series, hourly averages.... 49

Figure 40. CGO in-situ N₂O data (GC-MD) (1993-2023) provided by AGAGE. All valid data are shown. Top: Time series, hourly averages.... 50

Figure 41. CGO N₂O flask data (1991-2023) submitted to WDCGG by CSIRO. Top: Time series, hourly averages. Bottom: Left: frequency distribution,... 50

Figure 42. CGO N₂O flask data (1994-2014) submitted to WDCGG by NOAA. Top: Time series, hourly averages. Bottom: Left: frequency distribution,... 51

Figure 43. CGO N₂O flask data (1996-2023) submitted to WDCGG by NOAA. Top: Time series, hourly averages. Bottom: Left: frequency distribution,... 51

Figure 44. Deviations between Travelling Standard (TS) and Standard Reference Photometer (SRP) before and after use of the TS in the field 68

Figure 45. Results of the WCC-Empa TS calibrations for CH₄, CO₂, N₂O and CO. Only the values of the red solid circles were considered for averaging.... 72

Figure 46. Results of the WCC-Empa TS calibrations for CH₄, CO₂, N₂O and CO. Only the values of the red solid circles were considered for averaging.... 73

Figure 47. CH₄ (left panel) and CO₂ (right panel) calibrations of the WCC-Empa-TI. The top panel shows the raw 1 min values of the working standard and... 75

Figure 48. CO calibrations of the WCC-Empa-TI. The panels with the orange dots show the raw 1 min values of the working standards and the Loess fit... 76

Figure 49. CO calibration function based on the average values of the drift corrected working standard measurements 76