Combined 14CO2 and CO Observations:

A key to high-resolution fossil fuel CO2 records ? !

Ingeborg Levin1 and Ute Karstens2

1Institut für Umweltphysik Universität Heidelberg

2Max-Planck-Institut für Biogeochemie, Jena

Outline• Importance of fossil fuel CO2 emissions for the CO2

mixing ratio over Europe

• Determination of atmospheric fossil fuel CO2 by 14CO2 observations

• Correlation fossil fuel CO2 with CO

• Assessment of a purely observation-based method to derive hourly atmospheric fossil fuel CO2

Schauinsland station of the Umweltbundesamt in the Black Forst 1205 m

a.s.l.

Comparison of REMO-simulated CO2 mixing ratios at Schauinsland with observations

February 2002

July 2002

How can we measure fossil fuel CO2 in the atmosphere to validate these

model results ?

Radiocarbon 14C (14C, radioactive lifetime = 8300 years)

Natural 14C production by reactions of neutrons from cosmic radiation with atmospheric Nitrogen natural atmospheric background level

Artificial 14C production via atmospheric nuclear weapon tests in the 1950s and 1960s

„Negative 14C source“ via burning of fossil fuels and cement production which are free of 14C

Monthly mean fossil fuel CO2 at Schauinsland station and in Heidelberg

mean fossil fuel CO2 offset:

Schauinsland:ca. 1.4 ppm

Heidelberg:ca. 10 ppm

0

50

100

150

200

Jungfraujoch (cont. reference) Schauinsland monthly means Heidelberg monthly means

14

C [‰

]

0

5

10Schauinsland

1985 1990 1995 2000 20050

20

40 total CO

2 offset

fossil fuel offset

Heidelberg

foss

il fu

el C

O2 [p

pm]

The temporal resolution of 14C-derived fossil fuel CO2 is not sufficient to validate high-resolution

model simulations

Heidelberg sampling site in the populated Rhine valley

How well do CO mixing ratios correlate with fossil fuel CO2 ?

Use a combination of integrated 14CO2 and hourly CO measurements :

weeklymeashourly

basedCweekly2meas

hourlyhourly2CO

)foss(COCO)foss(CO

14

Test this approach in the REMO model world :

weeklymodhourly

weeklymodhourly2

modhourly

calculatedrehourly2

CO

)foss(COCO)foss(CO

Assess the difference between original and re-calculated hourly CO2(foss) -> RMS deviation

Test with REMO model run for Heidelberg

Annual mean CO2 foss [ppm] RMS error [ppm] RMS error [%]:

IER: 18.0 3.2 18EDGAR: 16.1 2.3 14

REMO-simulated fossil fuel CO2 in Europe and RMS difference to CO-based approach (Feb.

2002)

→ In most of Europe the CO-based method has RMS errors below 30%

Fossil fuel CO2 RMS error

Can we validate our suggested method to derive fossil fuel CO2 from integrated

14CO2 and hourly CO observations in the real world ?

23.04.2002 24.04.2002380

400

420

440

460 CO

2(foss) 14C-based

CO2(foss) CO-based

CO2 flasks

CO2 continuous

CO

2 [ppm

]

15.08.2002 16.08.2002

380

400

420

440

460

480 CO2(foss) 14C-based CO

2(foss) CO-based

CO2 flasks

CO2 continuous

CO

2 [ppm

]

Event samples collected in Heidelberg [data from Gamnitzer et al., 2006]

RMS deviation: 34 % RMS deviation: 32 %

RMS deviation: 23 % RMS deviation: 20 % 25.02.2003 26.02.2003 27.02.2003

400

450

500

550 CO2(foss) 14C-based

CO2(foss) CO-based

CO2 flasks CO

2 continuous

CO

2 [ppm

]

30.10.2002 31.10.2002380400420440460480500

CO2(foss) 14C-based

CO2(foss) CO-based

CO2 flasks

CO2 continuous

CO

2 [ppm

]

Summary :• Fossil fuel CO2 emissions in Europe contribute between 30% and 50% to

the atmospheric short-term (diurnal) CO2 signal and also to the monthly mean continental signal both, at urban and remote (mountain) sites

• CO is a good surrogate tracer for FFCO2 if well calibrated with 14CO2 observations, and can thus provide FFCO2 at high temporal resolution

• But: Calibration needs to be an ongoing exercise

• Combined weekly or two-weekly integrated 14CO2 and hourly CO observations allow to determine hourly fossil fuel CO in Europe with uncertainties between 15 and 40% (depending on the relative importance of the fossil fuel CO2 component)

• Our proposed method is purely observation-based and until now much more accurate and precise than any model-simulated approach [see Poster No. 179 by Karstens et al. ]

Suggestion for CarboEurope stations :

Establish high-precision integrated 14CO2 measurements at all stations where continuous CO measurements exist to “measure” hourly fossil fuel CO2 mixing ratios.

Thank you !

Test with REMO model run for Lutjewad

Annual mean CO2 foss [ppm] RMS error [ppm] RMS error [%]:

IER: 7.3 2.1 29EDGAR: 6.0 1.5 24

Test with REMO model run for Schauinsland

Annual mean CO2 foss [ppm] RMS error [ppm] RMS error [%]:

IER: 2.3 0.9 39EDGAR: 2.1 0.7 35

Continuous CO2 and CO mixing ratios in Heidelberg

01.02.2002 04.02.2002 07.02.2002 10.02.2002

250

500

750

1000

1250

01.02.2002 04.02.2002 07.02.2002 10.02.2002

380

400

420

440

460 CO

2 continuous

CO

2 [ppm

] CO continuous

CO

[ppb

]

11.07.2002 14.07.2002 17.07.2002 20.07.2002

250

500

750

1000

1250

11.07.2002 14.07.2002 17.07.2002 20.07.2002

380

400

420

440

460 CO2 continuous

CO

2 [ppm

] CO continuous

CO

[ppb

]

February2002

July2002

January 2002 CO2 Fluxes

Fossil fuel CO2 (extrap.)(Scholz et al., IER 2005)

Biome-BGC NEE (Churkina et al., 2003)

in 10-9 kg C m-2 s-1

IER: Inst. of Energy Economics and the Rational Use of Energy, Univ. Stuttgart, Germany

Calculation of the fossil fuel CO2 component from 14C observations

-120

-100

-80

-60

-40

-20

00 10 20 30 40

cbackground + cbio fossil CO2 offset [ppm]

14C

dep

letio

n [‰

]

1000CCCcc

BG14

meas14

BG14

measfossil