Atmospheric Oxygen in and above ForestsBritton 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 O2:CO2 relationships for global carbon budgeting

Plant physiology and nutrient cycling

Fossil fuel emission characterization and verification

Continental atmospheric transport of oceanic O2 signals

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)

Fuel-Cell Oxygen Analyzer (cont.)

Previous results:

-1.2 from a soil incubation study [J. Severinghaus]

-1.05 from a wood composition survey [R. Keeling]

O2 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 CO2 Sources

[R. Keeling, 1995]

Mexico

Expected ratio =

-1.46 mol O2:mol CO2

Expected ratio =

-1.13 mol O2:mol CO2

People’s Republic of China

Expected ratio =

-1.44 mol O2:mol CO2

United States of America

[from Marland, Boden, and Andres, http://cdiac.esd.ornl.gov]

-200

-300

-400

400

380

360

per meg O2/N2

ppm CO2

Average diurnal cycles for O2 (panel tops) and CO2 (panel bottoms)

Monthly O2:CO2 and standard errors from ODR fitJu

ne,

2000

Janu

ary

200

1 July

, 20

01

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.

-O2:CO2

PQ = 1.05

OR = 1.15

WLEF Comparison to Scripps CBA Curves

Blue Box and Controller

RAF Oxygen Analyzer (ROXAN)Vacuum Ultraviolet Absorption – 3 per meg rms on in 6 seconds

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 O2 fluxes