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An Autonomous Inexpensive Robust CO 2 Analyzer (AIRCOA) Britton Stephens, Andrew Watt, and Gordon Maclean National Center for Atmospheric Research, Boulder,

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Presentation on theme: "An Autonomous Inexpensive Robust CO 2 Analyzer (AIRCOA) Britton Stephens, Andrew Watt, and Gordon Maclean National Center for Atmospheric Research, Boulder,"— Presentation transcript:

1 An Autonomous Inexpensive Robust CO 2 Analyzer (AIRCOA) Britton Stephens, Andrew Watt, and Gordon Maclean National Center for Atmospheric Research, Boulder, Colorado, USA

2

3 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

4 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

5 NCAR CO 2 and O 2 /N 2 Calibration Facility

6 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

7 CO 2 signal averaged over 2.5 min. measurement cycle

8 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

9 Calibration sequence

10 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

11 Empirical pressure correction

12 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

13 SPL 9/4-9/18 NWR 9/18 Empirical temperature correction

14 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

15 Drying system monitoring A change of 0.5% RH is approximately 300 ppm H 2 O, which would cause a dilution error of 0.1 ppm in CO 2

16 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

17 Nafion absorption effect Flow pulled through Nafion went from 300 to 50 sccm at t = 30 sec

18 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

19 Empirical flushing correction

20 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

21 Automated (4- or 8-hourly) leak checks A positive trend of 0.3 kPa/min would be a leak rate of 0.1 sccm which if 100 ppm different would cause a 0.1 ppm bias

22 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

23 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

24 13 C bias test

25 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

26 Three cylinders were in the oven and one (green dots) was not Regulator oven tests

27 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

28 Regulator flushing tests

29 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

30 Laboratory intercomparisons Field surveillance tanks Laboratory offsets less than 0.06 ppm (1-sigma = 0.12 ppm) Field differences from assigned values less than 0.15 ppm (1-sigma = 0.15 ppm)

31 Potential source of biasAIRCOA solution Relating to WMO CO 2 ScaleDedicated CO 2 and O 2 calibration transfer facility Short-term IRGA noiseAverage for 2 minutes to get better than 0.1 ppm precision Drift in IRGA sensitivity4-hourly 4-point calibrations and 30-minute 1-point calibrations IRGA pressure sensitivityAutomated 4-hourly pressure sensitivity measurements IRGA temperature sensitivity30-minute 1-point calibrations, temperature control at some sites Incomplete drying of airSlow enough flow (100 sccm), two 96” Nafion driers, downstream humidity sensor to verify performance Drying system altering CO 2 Continuous flows and pressures through Nafions and run surveillance gas through entire system Incomplete flushing of cell and dead volumes Fast enough flow (100 sccm), alternate calibration sequence low ‑ to- high / high-to-low to look for effects Leaks through fittings, solenoid valves, and pumps Automated 8-hourly positive pressure leak-down and 4-hourly ambient pressure leak-up checks Pressure broadening without ArUse calibration gases made with real air Fossil CO 2 in calibration gases and different field and lab 13 C sensitivities Laboratory tests limit current effect to 0.05 ppm, long-term plans to use cylinders with natural CO 2 Regulator temperature effectsTests suggest effect is negligible, but could be regulator dependent Regulator flushing effectsRepeat calibration tests suggest the effect is negligible Whole-system diagnostics and comparability verification Long-term surveillance tank analyzed every 8 hours, co-location with other programs, rotating cylinders, and laboratory comparisons Delay in diagnosis of errorsNear real-time data acquisition, processing, and dissemination

32 Automated web-based output http://www.eol.ucar.edu/~stephens/RACCOON

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