1. Evaluating the Role of the CO 2 Source from CO Oxidation P. Suntharalingam Harvard University TRANSCOM Meeting, Tsukuba June 14-18, 2004 Collaborators : J. Randerson, J. A. Logan, D. J. Jacob, N. Krakauer, Y. Xiao, R. M. Yantosca, Acknowledgements : NOAA OGP Global Carbon Cycle Program, NASA Carbon Cycle Program

2. CARBON FLUX FRAMEWORK UNDERLYING MANY ATMOSPHERIC CO 2 INVERSIONS FossilBiosphereLand use Change Ocean 1.6 0.5 6 120 Units = Pg C/yr Atmospheric CO 2 90 92

3. TROPOSPHERIC CO OXIDATION IS A SOURCE OF ATMOSPHERIC CO 2 FossilBiosphere, Land use change, Agriculture, Biomass burning Ocean ATMOSPHERIC CO 2 ATMOSPHERIC CO CO, CH 4, NMHCs 0.9-1.2 Pg C/yr

4. REDUCED CARBON GASES ARE ACCOUNTED FOR IN EMISSIONS INVENTORIES BUT EMITTED AS CO 2 Fossil fuel : CO 2 emissions based on carbon content of fuel and assuming complete oxidation of CO and volatile hydrocarbons. (Marland and Rotty, 1984; Andres et al. 1996) CASA neutral biosphere : Biospheric C efflux represents respiration (CO 2 ) and emissions of reduced C gases (biogenic hydrocarbons, CH 4,etc) (Randerson et al., 2002; Randerson et al. 1997) CASA Neutral Biosphere Fossil Fuel

5. ANALYSIS FOCUS: Evaluating the “ Chemical Pump ” Effect IMPLICATIONS FOR FLUX ESTIMATES FROM CO 2 INVERSIONS OF MODELING REDUCED C CONTRIBUTION TO CO 2 AT SURFACE RATHER THAN AT OXIDATION SITE IN TROPOSPHERE STEP 1 : Evaluate impact on modeled concentrations STEP 2 : Implications for atmospheric inversions and estimated fluxes Previous related analyses : Enting and Mansbridge [1991]; Baker [2001] CO 2 from reduced C gases VS. CO 2 source from CO oxidation Surface Source Tropospheric Source

6. EVALUATION OF THE CHEMICAL PUMP EFFECT Calculate ADJUSTMENT  z model to Model Concentrations 1)Flux estimates from atmospheric inversions are based on difference between modeled and observed CO 2 concentrations : z model – z obs 2) Adjust z model to account for redistribution of reduced gas C from surface inventories to oxidation location in troposphere 3)Adjustment  z model = z COox – z RedC ADD effect of CO oxidation source of CO 2 SUBTRACT effect of reduced C from surface inventories Total carbon source conserved between z COox and z RedC simulations

7. EVALUATION OF THE CHEMICAL PUMP EFFECT ANALYSIS SETUP USING THE GEOS-CHEM MODEL Standard Simulation CO 2 Source from CO Oxidation = 1.1 Pg C/yr Distribute source according to seasonal 3-D variation of CO 2 production from CO Oxidation Distribute source according to seasonal SURFACE variations of reduced C emissions from Fossil and Biosphere sources CO2 RedC Simulation CO2 COox Simulation Simulations spun up for 3 years. Results from 4 th year of simulation

8. The GEOS-CHEM Model http://www-as.harvard.edu/chemistry/trop/geos/index.html Global 3-D model of atmospheric chemistry 2 o x2.5 o horizontal resolution; 30 vertical levels Driven by assimilated meteorology (GMAO) The CO simulation run to obtain CO oxidation distribution relies on archived OH fields (monthly) Emissions Distributions (spatial and temporal variability) Fossil : Andres et al. [1996] (annual mean) Biomass Burning : Duncan et al. [2003] (monthly) Biofuels : Yevich and Logan [2003] (annual mean) Biogenic hydrocarbons : Duncan et al. [2004], based on Guenther et al. [1995] (monthly) CH 4 emissions distributions : A priori from Wang et al. [2004] (monthly)

9. GLOBAL CO BUDGET SOURCES Duncan et al. 2004 Tg CO Pg C Recent Inverse Analyses * COMBUSTION Fossil Biomass Burning Biofuels TOTAL 465-490 450-570 190 1105-1250 0.47 – 0.55 * Bergamaschi et al. [2000]; Petron et al. [2002]; Kasibhatla et al. [2002] 1100-1530 0.47-0.65 BIOGENICS Isoprene, Monoterpenes, etc. 350-370 0.15-0.16 510-660 0.22-0.28 CH 4 OXIDATION 840-915 0.36-0.39 740-830 0.32-0.35 TOTAL 2290-2540 0.9-1.1 2846-3067 1.2-1.3 SINKS : Oxidation by OH STANDARD SIMULATION :CO 2 source from CO oxidation of 1.1 Pg C/yr

10. REDUCED CARBON SOURCES BY SECTOR STANDARD SIMULATION : CO 2 Source from CO Oxidation = 1.1 Pg C/yr * Methane sources distributed according to a priori fields from Wang et al. [2004] REDUCED CARBON SOURCES Pg C/yr Fossil (CO,CH 4,NMHCs)0.27 Biomass Burning (CO,CH 4,NMHCs)0.26 Biofuels (CO,CH 4 )0.09 Biogenic Hydrocarbons0.16 Other Methane Sources*0.31 TOTAL 1.1

11. CH 4 EMISSIONS AND BUDGET PROPORTIONS Standard Simulation :CH 4 Oxidation to CO = 0.39 Pg C/yr CH 4 emissions distributions and budget proportions from the a priori distribution of Wang et al. [2004] Rice 11% Wetlands 36% Termites 5% Biomass Burning 4% Fossil 16% Landfills 10% Biofuel 2% Livestock 11%

12. Source Distributions : Annual Mean Zonal Integral of Emissions Latitude CO2 COox : Column Integral of CO 2 from CO Oxidation CO2 RedC :CO 2 Emissions from Reduced C Sources CO2 COox :Maximum in tropics, diffuse CO2 RedC : Localized, corresponding to regions of high CO, CH 4 and biogenic NMHC emissions CO2 COox CO2 RedC gC/(cm 2 yr)

13. SURFACE CONCENTRATIONS : Annual Mean CO2 RedC  D modelCO2 CO2 COox Chemical Pump Adjustment

14. ZONAL AVERAGE : CHEMICAL PUMP EFFECT  D modelCO2 at Surface CO2 (ppm) Mean Interhemispheric difference = - 0.21 ppm 0.8 ppm Fossil : Surface, annual mean 1 Pg Fossil fuel CO 2 source gives interhemispheric difference of 0.81 ppm at surface, in GEOS-CHEM model 0.21 ppm Latitude

15. CHEMICAL PUMP EFFECT AT GLOBALVIEW SITES USED IN TRANSCOM LEVEL 1 INVERSION TRANSCOM Level 1 Inversion residuals from Gurney et al. 2002 Mean interhemispheric difference at TRANSCOM sites = 0.2 ppm

16. REGIONAL VARIATION OF CHEMICAL PUMP EFFECT Largest changes in regions in and downstream of high reduced C emissions TAP : - 0.55; ITN : - 0.35; BAL : - 0.35 (ppm)

17. IMPACT ON SURFACE FLUX ESTIMATES INTERHEMISPHERIC DIFFERENCE AT GLOBALVIEW SITES (ppm) DECREASE IN NHEM LAND CO 2 UPTAKE (Pg C/yr) Standard Simulation - 0.2 0.2 High CO (Petron et al. 2002) Increased Fossil+Biofuel emissions of 0.12 Pg C/yr - 0.27 0.3 Preliminary inversion results from J. Randerson, N. Krakauer TRANSCOM Level 1 inversion MATCH model

18. SUMMARY The atmospheric chemical pump has important implications for modeled CO 2 concentrations and inversion flux estimates. A CO oxidation source of 1.1 Pg C/yr gives a reduction in the modeled annual mean N-S gradient of 0.2 ppm (equivalent to a reduction of 0.2 Pg C/yr in Northern Hemispheric land uptake in an annual mean inversion.) Regional changes are larger; up to 0.6 ppm in regions of high reduced C emissions. Seasonal variations and sensitivities to model assumptions will be explored in future work. We can provide the reduced C source distributions (3D and surface) to TRANSCOM modelers to calculate their own model-specific chemical pump adjustments.