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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, Colorado, USA. Using high frequency data makes signals bigger, but the annual-mean signals are still very small:.

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An Autonomous Inexpensive Robust CO2 Analyzer (AIRCOA)

Britton Stephens, Andrew Watt, and Gordon Maclean

National Center for Atmospheric Research, Boulder, Colorado, USA


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).


NCAR CO annual-mean signals are still very small:2 and O2/N2 Calibration Facility


CO annual-mean signals are still very small:2 signal averaged over 2.5 min. measurement cycle


Calibration sequence annual-mean signals are still very small:


Empirical pressure correction annual-mean signals are still very small:


Empirical temperature correction annual-mean signals are still very small:

SPL 9/4-9/18

NWR 9/18


Drying system monitoring annual-mean signals are still very small:

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


Nafion absorption effect annual-mean signals are still very small:

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


Empirical flushing correction annual-mean signals are still very small:


Automated (4- or 8-hourly) leak checks annual-mean signals are still very small:

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


Regulator oven tests annual-mean signals are still very small:

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


Regulator flushing tests annual-mean signals are still very small:


Laboratory intercomparisons annual-mean signals are still very small:

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)


Automated web-based output annual-mean signals are still very small:

http://www.eol.ucar.edu/~stephens/RACCOON


Power budget
Power Budget annual-mean signals are still very small:


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