An Autonomous Inexpensive Robust CO
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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 CO 2 Analyzer (AIRCOA)

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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 CO2 and O2/N2 Calibration Facility


CO2 signal averaged over 2.5 min. measurement cycle


Calibration sequence


Empirical pressure correction


Empirical temperature correction

SPL 9/4-9/18

NWR 9/18


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


Nafion absorption effect

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


Empirical flushing correction


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


Regulator oven tests

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


Regulator flushing tests


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)


Automated web-based output

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


Power Budget


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