Atmospheric Carbon Observations Britton Stephens NCAR Atmospheric Technology Division Existing measurements: - Absolute and relative - In situ and flask Future capabilities: - Increased vertical profiles - Continental sensor arrays - Upward looking FTIR - Satellite measurements - Additional species

Atmospheric signals are small Rates of change in vertical column abundance for specific CO 2 sources and sinks SourceAssumptionsppm/day Los Angeles Basin 12  10 6 people, 4,000 km 2, 1100 mol C / person / day +10 Netherlands 16  10 6 people, 40,000 km 2, 500 mol C / person / day +0.6 Germany 83  10 6 people, 350,000 km 2, 580 mol C / person / day +0.4 Photosynthetic UptakeHarvard Forest, July-1.2 U.S. Carbon Sink1 GtCyr -1, constant in time, uniform over the lower 48 states Southern Oceans  pCO 2 = -30  atm, wind 15 m/s Eastern Equatorial Pacific  pCO 2 = 100  atm, wind 7 m/s +0.04

Absolute Measurement Techniques: Manometric and Gravimetric NOAA/CMDL Manometer: Reproducibility of 0.06 ppm for dry mole fraction of CO 2 (C. Zhao et al., 1997)

Relative measurement techniques: Infrared Absorption CMDL Flask Analysis System LiCor, Inc. CO 2 Analyzer

Intra- and Inter-laboratory agreement still not better than 0.2 ppm [NOAA/CMDL]

13 CO 2 / 12 CO 2 and O 2 /N 2 Ratios  Independent constraints on the land-ocean partitioning of CO 2 fluxes [NOAA/CMDL] [R. Keeling, SIO]

CO 2 Observational Platforms

Expected from fossil fuel emissions Observations TransCom1 FF Gradients What do existing flask measurements tell us?

 Longitudinal separation of continental sources North America versus Eurasia South America versus Africa What don’t they tell us?  Regional fluxes on scales relevant to the underlying processes  Vertical distributions to improve flux constraints and to reject flawed models

TURC/NDVI Biosphere Takahashi Ocean EDGAR Fossil Fuel [U. Karstens and M. Heimann, 2001] Continental mixed-layer CO 2 is highly variable [LSCOP, 2002]

Efforts coordinated by NOAA/CMDL SBIR Atmospheric Observing Systems 0.1 ppm in one minute Deployable for 6 months Towers, buoys, ships, planes Approximate cost: $20,000 Automated Flask Sampling Robust, Precise, CO 2 Analyzer for Unattended Field Use

Prototype Inexpensive/Autonomous CO 2 System Research items: Stability of CO 2 in aluminum LPG cylinders Correction for zero drift between calibrations Goals: 1-2 year service schedule Total installation ~ $ ppm accuracy RMT, Ltd., Russia

Towers over 650 feet AGL in U.S. and proximity

Upward Looking FTIR Spectrometry Sun following spectrometer Measure near infrared absorption of CO 2 and O 2 Demonstrated precision in U.S. and Russia to ~ 1.5 ppm in 30 minutes  Could validate satellite measurements  Should be validated by airborne measurements Kitt Peak Observatory

Advantages: Dramatic increase in CO 2 data, consistent global coverage, total column abundances, comparable to other datasets Disadvantages: Potential for biases due to aerosols, clouds, land surface type, viewing angle, or sun angle, expensive Existing or planned Techniques: Thermal Infrared Emission – TOVS, AIRS, IASI (2005)  Available, but primarily mid to upper troposphere Reflected Near Infrared – SCIAMACHY, OCO (ESSP Phase 2, 2006) Satellite CO 2 Measurements Targeted precision of better than 1 ppm for 4 x 5 degrees in 16 days

Flask (+) and in situ (-) measurements from COBRA-2000, made during a descent into Boston, MA. Additional measurement species

Flux footprint, in ppm(GtCyr -1 ) -1, for a 10 6 km 2 chaparral region in the U.S. Southwest (Gloor et al., 1999). Using high frequency data makes signals bigger, but the annual-mean signals are still very small: To measure 0.2 GtCyr-1 regional source or sink to +/- 25%, need to measure annual mean surface gradients to around +/- 0.2 ppm and column gradients to better than 0.1 ppm

Representativeness 360 m 120 m 800 m S Total representativity error of mixed layer averaged CO 2 mixing ratios (combined observational error and representativity error) plotted against the horizontal dimension of the region. Vertical bars indicate the 5-95% range. [Gerbig et al., submitted to JGR] COBRA-2000 Daytime Profiles

Conclusions Existing atmospheric measurements alone constrain fluxes of broad latitudinal zones Room for improvement by assimilating multiple existing data types Most significant advances will be from new measurement types and their assimilation Systematic biases in and representativeness of data must be considered carefully