This study uses atmospheric 14CO2 measurements to estimate fossil fuel (ff) CO2 emission hotspots in an urban area along the Rhine valley. Two approaches are compared: 1) an upwind-downwind approach using paired stations to estimate background levels, and 2) a regional background approach. The ffCO2 concentrations ranged from 0-10 ppm. Uncertainties were about 1.2 ppm for the upwind-downwind approach and 50-100% higher for the regional approach. There was also a strong correlation found between total CO2 and ffCO2 offsets across the study area, indicating total CO2 can serve as a proxy for ffCO2. However, accounting for nuclear 14C contamination remained challenging

1. Monitoring ffCO₂ emission hotspots
using atmospheric ¹⁴CO₂ measurements
1 ICOS Central Radiocarbon Laboratory, Germany
2 IUP, Heidelberg University, Germany
S. Hammer1,2, T. Kneuer2, F. Maier2, C. Rieß2, J. Della Coletta1,
S. Preunkert1,3, I. Storm4, U. Karstens4 and I. Levin2
3 IGE, Université Grenoble Alpes, France
4 ICOS Carbon Portal, Sweden

2. Estimating the fossil fuel CO2 concentration
enhancement of an urban emission area
• Lagrangian up- and downwindapproach
• Use 14CO2 to separate ff and bio CO2
contributions
Urban emission area
2

3. Estimating the fossil fuel CO2 concentration
enhancement of an urban emission area
• Lagrangian up- and downwindapproach
• Use 14CO2 to separate ff and bio CO2
contributions
Upwind
station
Downwind
station
Urban emission area
3

4. Estimating the fossil fuel CO2 concentration
enhancement of an urban emission area
• Lagrangian up- and downwindapproach
• Use 14CO2 to separate ff and bio CO2
contributions
Upwind
station
Downwind
station
Urban emission area
• INFLUX was the pioneer for
Lagrangian urban CO2 networks
INFLUXexperiment
Richardson, et al., Elem.
Sci. Anth (2017).
4

5. RINGO approach:
• Investigate synergies with the ICOS
atmosphere network to perform
urban upwind and downwind
measurements. (poor men's
INFLUX).
• Model supported sampling strategy
to ensure the best possible
approximation of Lagrangian
conditions.
FRE
HEI
CO2 emission data
provided by TNO
5

6. Open questions…
• Which background measurement can be
used for 14CO2-based ffCO2 estimates?
• Does nuclear 14C contamination influence
this choice?
• Is the total CO2- offset a good proxy for
the fossil fuel CO2 enhancement?
FRE
HEI
SSL
@ 1100m NN
Photo:ChristophZinsius/UBA
CO2 emission
data provided
by TNO
6

7. 7
14CO2 observations in the Rhine valley

8. 14CO2 observations in the Rhine valley
8
Assume you have 100 14CO2 samples, which sampling strategy will
provide the better ffCO2 estimate during the dormant season?

9. 14CO2 observations in the Rhine valley
9
Assume you have 100 14CO2 samples, which sampling strategy will
provide the better ffCO2 estimate during the dormant season?
Strategy A:
up- / downwind approach
I happily spend half of my
samples to have a better
estimate of the background
conditions!

10. 14CO2 observations in the Rhine valley
10
Assume you have 100 14CO2 samples, which sampling strategy will
provide the better ffCO2 estimate during the dormant season?
Strategy B:
regional BG approach
I accept a larger
background uncertainty,
but I get twice the
downwind samples!
Strategy A:
up- / downwind approach
I happily spend half of my
samples to have a better
estimate of the background
conditions!

11. 14CO2 observations in the Rhine valley
11

12. 14CO2 observations – corrected for 14Cnuc
12

13. 14CO2 observations – corrected for 14Cnuc
• Std. dev. of upwind samples from the
BG-fit: 4.3‰ during dormant season.
• Average difference: 0.2 ‰.
13
Std. dev.:
4.3‰

14. 14CO2 observations – corrected for 14Cnuc
14

15. 14CO2 observations – corrected for 14Cnuc
• magnitude of nuc. correction varies
• nuc. correction largely inherent in
the two-station approach
15

16. Annual mean nuc 14C emissions:
WRF: - ERA-5 (0.25°)
- 2 km x 2 km
STILT: - ECMWF op. Analysis (0.25°)
- 10 km x 10 km
Is the modelled nuclear 14C correction reliable?
WRF: nuccorr= 0.6 ‰ STILT: nuccorr= 8.2 ‰
RAdioactive Dis-
chargesDatabase
16
Footprint
240h back
Footprint
72 h back

17. 0 1 2 3 4 5 6 7 8 9 10 11 12 13
0
5
10
15
STILT
WRF
nucinfluenceD14
CO2[‰]
flask no.
Nuclear 14C contributions from WRF and STILT
analytical
14C uncertainty
17

18. ffCO2 uncertainty budget for different 14CO2-BGs
Upwind / downwind
approach
Uncertainties Regional BG
approach
2.3 ‰ Background estimate 4.3 ‰
2.3 ‰ Downwind measurement 2.3 ‰
all
both models
agree
0.5 ‰ Footprint 14Cnuc correction 4 ‰ 1 ‰
0.5 ‰ 14Cnuc emi strength (err. 100%) 2 ‰ 1 ‰
3.3 ‰ ~
1.2ppm ffCO2
Total
6.6 ‰ ~
2.4ppm ffCO2
5.1 ‰ ~
1.8ppm ffCO2
18

19. Up-/downwind vs. regional ffCO2 estimates
19

20. Up-/downwind vs. regional ffCO2 estimates
20

21. Up-/downwind vs. regional ffCO2 estimates
21

22. Up-/downwind vs. regional ffCO2 estimates
22

23. Summary
• Synergies with ICOS stations can be used to investigate emissions
from nearby urban areas.
• ffCO2 concentrations in the Rhine valley experiment range between
0 ppm and 10 ppm.
• ffCO2 uncertainties are about 1.2ppm in the up-/downwind approach
and 50% to 100% larger in the regional background approach.
23

24. Open questions…
• Which background measurement can be
used for 14CO2-based ffCO2 estimates?
• Does nuclear 14C contamination influence
this choice?
• Is the total CO2- offset a good proxy for
the fossil fuel CO2 enhancement?
FRE
HEI
SSL
@ 1100m NN
Photo:ChristophZinsius/UBA
CO2 emission
data provided
by TNO
24

25. -2 0 2 4 6 8 10 12 14
-2
0
2
4
6
8
10
12
ffCO2[ppm]
up-/downwindapproach
total CO2 difference [ppm] (down - upwind)
1:1
ffCO2 share on the total CO2 difference
slope = 1.09 ± 0.16
R² = 0.76
25

26. -2 0 2 4 6 8 10 12 14
-2
0
2
4
6
8
10
12
ffCO2[ppm]
up-/downwindapproach
total CO2 difference [ppm] (down - upwind)
1:1
ffCO2 share on the total CO2 difference
slope = 1.09 ± 0.16
R² = 0.76
26

27. -2 0 2 4 6 8 10 12 14
-2
0
2
4
6
8
10
12
ffCO2[ppm]
up-/downwindapproach
total CO2 difference [ppm] (down - upwind)
1:1
ffCO2 share on the total CO2 difference
slope = 1.09 ± 0.16
R² = 0.76
Bio
Fossil fuel
27

28. Summary
• Synergies with ICOS stations can be used to investigate emissions
from nearby urban areas.
• ffCO2 concentrations in the Rhine valley experiment range between
0 ppm and 10 ppm.
• ffCO2 uncertainties are about 1.2ppm in the up-/downwind approach
and 50% to 100% larger in the regional background approach.
• Strong correlation between the total CO2 and the ffCO2 offset across
the Rhine valley area.
28

29. Annual mean nuc 14C emissions:
WRF: - ERA-5 (0.25°)
- 2 km x 2 km
STILT: - ECMWF op. Analysis (0.25°)
- 10 km x 10 km
Is the modelled nuclear 14C correction reliable?
WRF: nuccorr= 21.4 ‰ STILT: nuccorr= 1.1 ‰
RAdioactive Dis-
chargesDatabase
29