1. Atmospheric Oxygen in and above Forests Britton Stephens, National Center for Atmospheric Research, Boulder, Colorado, USA Harvard Forest, Massachusetts, USA VUV Absorption, August 1998 WLEF Tall Tower, Wisconsin, USA Fuel Cell, June 2000 – November 2003 Applications:  Terrestrial O 2 :CO 2 relationships for global carbon budgeting  Plant physiology and nutrient cycling  Fossil fuel emission characterization and verification  Continental atmospheric transport of oceanic O 2 signals

2. Fuel-Cell Oxygen Analyzer Off the shelf: 25 per meg rms in 1 sec and ~100 per meg hourly drift Modifications: –removed plastic tubing and filters –removed heat exchanger –common outlet plumbing –cryogenic drying –active pressure and flow control –multiple inlets and reference gases –1-minute switching cycle –inlet pick-off tees Resulting Precision: –2.5 per meg rms on  in 2 minutes –1.5 per meg rms on a 6 minute measurement every 20 minutes –2.5 per meg drift over 6 hours Sable Systems, NV (S/N OX0001 ‑ 02)

3. Fuel-Cell Oxygen Analyzer (cont.)

4. Previous results: -1.2 from a soil incubation study [J. Severinghaus] -1.05 from a wood composition survey [R. Keeling]

7. O 2 in urban pollution studies and emission verification 0.0Cement Production -1.98 ± 0.07Gas Flaring -1.95 ± 0.04Natural Gas -1.44 ± 0.03Liquid Fuel -1.17 ± 0.03Coal Oxidative Ratios for CO 2 Sources [R. Keeling, 1995] Mexico Expected ratio = -1.46 mol O 2 :mol CO 2 Expected ratio = -1.13 mol O 2 :mol CO 2 People’s Republic of China Expected ratio = -1.44 mol O 2 :mol CO 2 United States of America [from Marland, Boden, and Andres, http://cdiac.esd.ornl.gov]

8. -200 -300 -400 400 380 360 per meg O 2 /N 2 ppm CO 2 Average diurnal cycles for O 2 (panel tops) and CO 2 (panel bottoms)

9. Monthly O 2 :CO 2 and standard errors from ODR fit June, 2000 January 2001 July, 2001 Q. What do these numbers actually represent? A1. Complex combinations of local photosynthesis and respiration influences and synoptic transport of terrestrial, industrial, and oceanic signals A2. Not likely equal to  B, but potentially related to forest growth state and nutrient partitioning.

10. -O 2 :CO 2 PQ = 1.05 OR = 1.15

12. WLEF Comparison to Scripps CBA Curves

15. Blue Box and Controller RAF Oxygen Analyzer (ROXAN) Vacuum Ultraviolet Absorption – 3 per meg rms on  in 6 seconds

16. Potential Future Directions Fuel-cell: –Restart at WLEF with well-characterized and improved accuracy –Deploy at another terrestrial site –Deploy on a ship –Deploy at South Pole VUV: –Cylinder calibrations –Airborne industrial, terrestrial, oceanic, and stratospheric studies –Wind-tunnel studies of aircraft inlet fractionation –Eddy-correlation measurements of air-sea O 2 fluxes