| Vacuum Ultraviolet (VUV) O2 Analyzer | ||
| While
a graduate student at Scripps
Institution of Oceanography from 1995 to 1999, I developed an
instrument for making very precise measurements of atmospheric
oxygen concentration that can be used to investigate terrestrial,
oceanic, and industrial biogeochemical processes. The instrument
works by detecting the absorption of vacuum
ultraviolet radiation. While laboratory techniques
of comparable precision existed, this was the first O2
instrument that could easily
be deployed at remote field sites and on moving platforms. I
field tested it during a cruise on the Scripps ship R/V Robert Gordon
Sproul,
and then deployed it on longer cruises on the NOAA ship Ka'imimoana
from San Diego to the Equator and back to Honolulu, and on the NSF ship
Lawrence M. Gould from Punta Arenas, Chile to Palmer Station,
Antarctica and back. I have also used the instrument to measure O2
variations for one month at Harvard Forest. Descriptions of the
instrument and results
from the two extended cruises can be found in my dissertation [Chapter
3 PDF; Chapter 4 PDF; Chapter 5 PDF; Entire document PDF] and a Tellus
paper [PDF]. Since moving to NCAR, I have made several improvements to the instrument, resolved its remaining motion sensitivity, and successfully tested it for airborne O2 measurements on the NCAR C130 during the IDEAS I and II campaigns. ROXAN (RAF Oxygen Analyzer) now has a precision of 3 per meg (approximately 0.6 parts per million) in 6 seconds. For comparison, this is equivalent to detecting the removal of one O2 molecule from 1.5 million molecules of air. The instrument is presently being rebuilt and will primarily be used in the laboratory as part of the NCAR CO2 and O2 Calibration Facility. A dedicated field unit will be built in the future, and made available as a community-requestable EOL resource. Planned applications for this VUV technique on airborne, ground-based, and shipboard platforms include partitioning terrestrial and oceanic CO2 fluxes on regional to global scales, identifying the mixture of fuel types in industrial emission plumes, investigating the levels of nitrification and wood production in forest ecosystems, resolving thermal and biological controls on air-sea CO2 fluxes, measuring O2 fluxes by eddy-correlation at free-air carbon enrichment (FACE) sites to estimate terrestrial net ecosystem exchange or at sea to constrain gas exchange rates, detecting gravitational fractionation in the stratosphere, and exploring potential fractionation effects at aircraft sampling inlets through wind tunnel studies. |
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