Atmospheric O2 Measurements in HIPPO (HIAPER Pole-to-Pole Observations of Atmospheric Tracers)

Britton Stephens, NCAR EOL and TIIMES

Careful atmospheric CO2 measurements since the 1950s show that about half of fossil fuel emissions remain in the atmosphere

FF

Atm

[IPCC, 2007]

[R. Keeling, SIO]

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 %

Global atmospheric inverse models and surface data have been used to make regional flux estimates

Forward: Flux + Transport = [CO2]

Inverse: [CO2] – Transport = Flux

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

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

[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

ppm

pres

sure

N S N S N S N S

Transcom3 Fossil Fuel Response

ppm

latitude

TransCom Seasonal APO Amplitude

T. Blaine, SIO Dissertation, 2005

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

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)

• 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)

RF13 6/16/08

Large-scale gradient at 38 kft

O2:CO2 ratios for Northern Hemisphere latitudinal gradients vary from -1.0 to -3.0

Initial climb-out from BJC

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]

Descent and missed approach over Missouri

RF15 6/23/08

Descent over LEF tower in Wisconsin

Descent into Grand Forks, ND

O2:CO2 ratios for Northern Hemisphere temporal trends vary from -4.0 to 4.0

RF16 6/24/08

Initial climb out of Grand Forks, ND

Fires and photosynthesis

Into / out of lower strat.

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