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Atmospheric O2 Measurements in HIPPO (HIAPER Pole-to-Pole Observations of Atmospheric Tracers)
Britton Stephens, NCAR EOL and TIIMES
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Careful atmospheric CO2 measurements since the 1950s show that about half of fossil fuel emissions remain in the atmosphere
FF
Atm
[IPCC, 2007]
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[R. Keeling, SIO]
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Annual fluxes are small relative to balanced seasonal exchanges and to standing pools
The global carbon cycle for the 1990s, showing the main annual fluxes in GtC yr –1. [IPCC, 2007]
Annual residuals
Land-Based Sink
Net Oceanic Sink
Pools and flows
Uncertainties on natural annual-mean ocean and land fluxes are +/- 25 to 75 %
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Global atmospheric inverse models and surface data have been used to make regional flux estimates
Forward: Flux + Transport = [CO2]
Inverse: [CO2] – Transport = Flux
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Regional land flux uncertainties are very large
• All model average and standard deviations:
Northern Land = -2.4 ± 1.1 PgCyr-1
Tropical Land = +1.8 ± 1.7 PgCyr-1
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Comparing the Observed and Modeled Gradients
Model Model Name
1 CSU
2 GCTM
3 UCB
4 UCI
5 JMA
6 MATCH.CCM3
7 MATCH.NCEP
8 MATCH.MACCM2
9 NIES
A NIRE
B TM2
C TM3
Most of the models overestimate the annual-mean vertical CO2 gradient
Observed value
• 3 models that most closely reproduce the observed annual-mean vertical CO2 gradients (4, 5, and C):
Northern Land = -1.5 ± 0.6 PgCyr-1
Tropical Land = +0.1 ± 0.8 PgCyr-1
• All model average:
Northern Land = -2.4 ± 1.1 PgCyr-1
Tropical Land = +1.8 ± 1.7 PgCyr-1
Northern Land
Tropical Land
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[Stephens et al., Science, 2007]
Airborne measurements suggest:
• Northern forests, including U.S. and Europe, are taking up much less CO2 than previously thought
• Intact tropical forests are strong carbon sinks and are playing a major role in offsetting carbon emissions
However, large (O ~ 2 PgCyr-1) flux uncertainties associated with modeling atmospheric CO2 transport remain
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ppm
pres
sure
N S N S N S N S
Transcom3 Fossil Fuel Response
ppm
latitude
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TransCom Seasonal APO Amplitude
T. Blaine, SIO Dissertation, 2005
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HIPPO (PIs: Harvard, NCAR, Scripps, and NOAA): A global and seasonal survey of CO2, O2, CH4, CO, N2O, H2, SF6, COS, CFCs, HCFCs, O3, H2O, and hydrocarbons
HIAPER Pole-to-Pole Observations of Atmospheric Tracers
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START-08/Pre-HIPPO Field Campaign
123 flight hours over six weeks in April/May and June of 2008START08 PIs: Laura Pan (NCAR), Elliot Atlas (Miami U), Kenneth Bowman (TAMU)HIPPO PIs: Steve Wofsy (Harvard), Britt Stephens (NCAR), Jim Elkins (NOAA), Ralph Keeling (Scripps)
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• measures O2 concentration (reported as O2/N2 ratio) using a vacuum-ultraviolet absorption technique
• based on earlier shipboard and laboratory instruments, but designed specifically for airborne use to minimize motion and thermal sensitivity and with a pressure and flow controlled inlet system
• switches between sample gas and air from a high-pressure reference cylinder every 2 seconds and has a precision of +/- 2 per meg on a 4-second measurement
• consists of a pump module, a cylinder module, an instrument module, and a dewar
NCAR Airborne Oxygen Instrument (AO2)
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RF13 6/16/08
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Large-scale gradient at 38 kft
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O2:CO2 ratios for Northern Hemisphere latitudinal gradients vary from -1.0 to -3.0
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Initial climb-out from BJC
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Atmospheric O2 measurements in urban pollution studies
Britton Stephens, NCAR ATD
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]
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Descent and missed approach over Missouri
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RF15 6/23/08
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Descent over LEF tower in Wisconsin
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Descent into Grand Forks, ND
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O2:CO2 ratios for Northern Hemisphere temporal trends vary from -4.0 to 4.0
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RF16 6/24/08
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Initial climb out of Grand Forks, ND
Fires and photosynthesis
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Into / out of lower strat.
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Conclusions
• Airborne O2 instrument is performing well and meaningful variations were observed from the surface to the stratosphere
• Data analysis / paper writing is underway and minor modifications are being made in anticipation of HIPPO global in January ‘09