An Autonomous Inexpensive Robust CO 2 Analyzer (AIRCOA)

1. An Autonomous Inexpensive Robust CO2 Analyzer (AIRCOA) Britton Stephens, Andrew Watt, and Gordon Maclean National Center for Atmospheric Research, Boulder, Colorado, USA

2. Using high frequency data makes signals bigger, but the annual-mean signals are still very small: To measure 0.2 GtCyr-1 source/sink to +/- 25% need to measure regional annual mean gradients to 0.1-0.2 ppm Flux footprint, in ppm(GtCyr-1)-1, for a 106 km2 chaparral region in the U.S. Southwest (Gloor et al., 1999).

6. NCAR CO2 and O2/N2 Calibration Facility

8. CO2 signal averaged over 2.5 min. measurement cycle

10. Calibration sequence

12. Empirical pressure correction

14. Empirical temperature correction SPL 9/4-9/18 NWR 9/18

16. Drying system monitoring A change of 0.5% RH is approximately 300 ppm H2O, which would cause a dilution error of 0.1 ppm in CO2

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

20. Empirical flushing correction

22. 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

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

28. Regulator flushing tests

30. Laboratory intercomparisons Laboratory offsets less than 0.05 ppm (1-sigma = 0.13 ppm) Field surveillance tanks 2.5-month average field differences from assigned values 0.01 to 0.10 ppm (1-sigma = 0.10 to 0.13 ppm)

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

33. Power Budget