Evaluating the Role of the CO2 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

CARBON FLUX FRAMEWORK UNDERLYING MANY ATMOSPHERIC CO2 INVERSIONS

Fossil Biosphere Land use Change

Ocean

1.6 0.5

6120 120

Units = Pg C/yr

Atmospheric CO2

9092

TROPOSPHERIC CO OXIDATION IS A SOURCE OF ATMOSPHERIC CO2

Fossil Biosphere, Land use change, Agriculture, Biomass burning

Ocean

ATMOSPHERIC CO2

ATMOSPHERIC CO

CO, CH4, NMHCs

0.9-1.2 Pg C/yr

REDUCED CARBON GASES ARE ACCOUNTED FOR IN EMISSIONS INVENTORIES BUT EMITTED AS CO2

Fossil fuel : CO2 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 (CO2) and emissions of reduced C gases (biogenic hydrocarbons, CH4,etc)

(Randerson et al. , 2002; Randerson et al. 1997)

CASA Neutral Biosphere

Fossil Fuel

ANALYSIS FOCUS: Evaluating the “Chemical Pump” Effect IMPLICATIONS FOR FLUX ESTIMATES FROM CO2 INVERSIONS OF MODELING

REDUCED C CONTRIBUTION TO CO2 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]

CO2 from reduced C gases

VS.CO2 source from CO oxidation

Surface Source Tropospheric Source

EVALUATION OF THE CHEMICAL PUMP EFFECTCalculate ADJUSTMENT zmodel to Model Concentrations

1) Flux estimates from atmospheric inversions are based on difference between modeled and observed CO2 concentrations : zmodel – zobs

2) Adjust zmodel to account for redistribution of reduced gas C from surface inventories to oxidation location in troposphere

3) Adjustmentzmodel = zCOox – zRedC

ADD effect of CO oxidation source of CO2

SUBTRACT effect of reduced C from surface inventories

Total carbon source conserved between zCOox and zRedC

simulations

EVALUATION OF THE CHEMICAL PUMP EFFECTANALYSIS SETUP USING THE GEOS-CHEM MODEL

Standard Simulation

CO2 Source from CO Oxidation = 1.1 Pg C/yr

Distribute source according to seasonal 3-D

variation of CO2 production from CO

Oxidation

Distribute source according to seasonal SURFACE variations of reduced C emissions from Fossil and Biosphere sources

CO2RedC SimulationCO2COox Simulation

Simulations spun up for 3 years. Results from 4th year of simulation

The GEOS-CHEM Modelhttp://www-as.harvard.edu/chemistry/trop/geos/index.html

•Global 3-D model of atmospheric chemistry

•2ox2.5o 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)

CH4 emissions distributions : A priori from Wang et al. [2004] (monthly)

GLOBAL CO BUDGETSOURCES Duncan et al. 2004

Tg CO Pg CRecent Inverse

Analyses*

COMBUSTIONFossilBiomass BurningBiofuelsTOTAL

465-490450-570

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

BIOGENICSIsoprene, Monoterpenes, etc.

350-370 0.15-0.16 510-660 0.22-0.28

CH4 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 :CO2 source from CO oxidation of 1.1 Pg C/yr

REDUCED CARBON SOURCES BY SECTOR STANDARD SIMULATION : CO2 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,CH4,NMHCs) 0.27

Biomass Burning (CO,CH4,NMHCs) 0.26

Biofuels (CO,CH4) 0.09

Biogenic Hydrocarbons 0.16

Other Methane Sources* 0.31

TOTAL 1.1

CH4 EMISSIONS AND BUDGET PROPORTIONS

Rice

Livestock

Wetlands

Termites

BiomassBurn

Fossil

Landfills

Biofuel

Standard Simulation :CH4 Oxidation to CO = 0.39 Pg C/yr

CH4 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%

Source Distributions : Annual Mean

Zonal Integral of Emissions

Latitude

CO2COox: Column Integral of

CO2 from CO OxidationCO2RedC :CO2 Emissions from

Reduced C Sources

CO2COox :Maximum in tropics, diffuse

CO2RedC : Localized, corresponding to regions of high CO, CH4 and biogenic NMHC emissions

CO2COox

CO2RedC

gC/(cm2 yr)

SURFACE CONCENTRATIONS : Annual Mean

CO2RedC

DmodelCO2

CO2COox

Chemical Pump Adjustment

ZONAL AVERAGE : CHEMICAL PUMP EFFECT

DmodelCO2 at

Surface

CO

2 (p

pm

)

Mean Interhemispheric

difference = - 0.21 ppm

0.8 ppm

Fossil : Surface, annual mean

1 Pg Fossil fuel CO2 source gives interhemispheric difference of 0.81 ppm at surface, in GEOS-CHEM model

0.21 ppm

Latitude

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

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)

IMPACT ON SURFACE FLUX ESTIMATES

INTERHEMISPHERIC DIFFERENCE AT

GLOBALVIEW SITES (ppm)

DECREASE IN NHEM LAND CO2

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

SUMMARY

•The atmospheric chemical pump has important implications for modeled CO2 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.