Atmospheric O 2 Measurements in HIPPO (HIAPER Pole-to- Pole Observations of Atmospheric Tracers) Britton Stephens, NCAR EOL and TIIMES

Careful atmospheric CO 2 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 = [CO 2 ] Inverse: [CO 2 ] – 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 ModelModel Name 1CSU 2GCTM 3UCB 4UCI 5JMA 6MATCH.CCM3 7MATCH.NCEP 8MATCH.MACCM2 9NIES ANIRE BTM2 CTM3 Most of the models overestimate the annual-mean vertical CO 2 gradient Observed value 3 models that most closely reproduce the observed annual-mean vertical CO 2 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 CO 2 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 CO 2 transport remain

ppm pressure NSNSNSNS 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 CO 2, O 2, CH 4, CO, N 2 O, H 2, SF 6, COS, CFCs, HCFCs, O 3, H 2 O, 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 2008 START08 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 O 2 concentration (reported as O 2 /N 2 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

O 2 :CO 2 ratios for Northern Hemisphere latitudinal gradients vary from -1.0 to -3.0

Initial climb-out from BJC

Atmospheric O 2 measurements in urban pollution studies Britton Stephens, NCAR ATD 0.0Cement Production ± 0.07Gas Flaring ± 0.04Natural Gas ± 0.03Liquid Fuel ± 0.03Coal Oxidative Ratios for CO 2 Sources [R. Keeling, 1995] Mexico Expected ratio = mol O 2 :mol CO 2 Expected ratio = mol O 2 :mol CO 2 People’s Republic of China Expected ratio = mol O 2 :mol CO 2 United States of America [from Marland, Boden, and Andres,

Descent and missed approach over Missouri

RF15 6/23/08

Descent over LEF tower in Wisconsin

Descent into Grand Forks, ND

O 2 :CO 2 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 O 2 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