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Home , Freiburg im Breisgau, Heidelberg, Schauinsland

13 Evaluation of continuous δ CH4 measurements in and at ,

Antje Hoheisel1, Frank Meinhardt2, Martina Schmidt1

(1) Institute of Environmental Physics, , Heidelberg, Germany (2) German Environment Agency UBA, Schauinsland, Germany

07.05.2020

[email protected]

EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 1 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt Measurement sites Heidelberg & Schauinsland

5 km In Heidelberg (116m a.s.l.), south-west Germany, a CRDS low mountain range G2201-i analyser has been used to continuously measure CH 4 industrial cities and and its 13C/12C ratio in ambient air at the Institute of Environ- mental Physics (IUP) since 2014. Heidelberg is in the North of the Upper valley, east of the low mountain range Oden- IUP Heidelberg wald and in the west of agricultural areas. The industrial cities agricultural areas Mannheim and Ludwigshafen are 15-20 km north-west. Germany

Rhine Valley

Heidelberg At the mountain station Schauinsland (1205m a.s.l.), oper-

ated by the German Environment Agency (UBA), the CH4 mole city im

fraction is measured since 1992. Schauinsland is on the edge Schauinsland of the to the Rhine valley, south-east of the city . Two measurement campaigns were per- UBA Schauinsland Schauinsland

formed at Schauinsland with the CRDS G2201-i analyser to Rhine Valley 13 monitor continuous δ CH4 measurements at a semi-rural sta- tion. mountain range Black Forest

5 km

Map data: Google Earth, 2020 Google; Image Landsat/Copernicus, 2020 GeoBasis-DE/BKG. Map data: Google Earth, 2020 Google;gg MapImage Landsat/Copernicus, data: Google 2020 GeoBasis-DE/BKG. Earth, 2020 Google; Image Landsat/Copernicus, 2020 GeoBasis-DE/BKG. EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 2 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt Isotopic composition of methane

The isotopic composition can be described using the h i ! 13CH Rsample 4 δ-notation. The CH4 mole fractions were calibrated against δ = − 1 · 1000 with 13R = the WMO scale (Dlugokencky et al., 2005) and the δ13CH val- R 12CH  4 standard h 4 ues of calibration gases were analysed at Max-Planck-Institute for Biogeochemistry (MPI-BGC) in (Sperlich et al., 2016). These analyses connect our Heidelberg measurements to the VPDB (Vienna Pee Dee Belemnite) isotope scale.

Analyses of the isotopic composition of CH4 results from mobile measurements in ambient air can potentially be used to dif- dairy farm average over mobile measurements ferentiate between different CH4 source cat- results from direct gas sampling egories. Isotopic signatures of CH4 sources biogas plant in the surrounding of Heidelberg were charac- terised (Hoheisel et al. 2019) and shown in the right figure. landfill CH4 emission enhancements measured in Heidelberg can origin from biogenic sources WWTP like dairy cows in the nearby farms and waste water treatment plants, thermogenic sources natural gas facility from the natural gas distribution system and even pyrogenic sources like traffic. −70 −65 −60 −55 −50 −45 −40 13 δ CH4 [‰]

EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 3 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt 13 Continuous CH4 and δ CH4 measurements in Heidelberg

2400 1day average 13 Since April 2014 CH4 and δ CH4 are mea- monthly mean sured continuously with a CRDS analyser in 2300 seasonal cycle Heidelberg. The daily mean CH4 mole frac- tion varies between 1890 and 2310 ppb with 2200

higher spikes in winter than in summer. [ppb] 4 2100 A seasonal cycle can be noticed. The maxi- DataT$CH4 H

mum mean CH4 mole fraction occurs in late C autumn (October-December). During winter 2000 and spring the mole fraction decreases slightly to the minimum in late summer (June-August). 1900 The high CH4 mole fractions in winter occur especially due to climatological conditions like −47.5 long lasting inversions, a much lower bound- DataT$decimaldate ary height and longer continental residence −48.0 times of air masses due to high pressure sys- [‰] 4

tems. H 13 δ CH shows more depleted values in - C −48.5

4 DataT$dCH4

tumn (Sep-Nov) and more enriched ones in 13 δ spring (Mar-May). −49.0

2015 2016 2017 2018 2019 2020

DataT$decimaldateyear

EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 4 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt 13 Comparison of CH4 and δ CH4 at different sites

time series annual cycle The CH4 mole fractions measured in Heidelberg (HD) and Schauinsland (SSL) are higher than at HD SSL (UBA) 60 the background station MaceHead (MHD). As Hei- MHD (NOAA/INSTAAR)* SSL_Campaigns 2100 MHD − 0.28‰ (intercomparison offset) delberg is an urban station located in the Rhine Val- 40 ley, the seasonal variations of the measured CH 4 2050 mole fraction at Heidelberg vary much stronger 20 than at the mountain station Schauinsland.

[ppb] 2000 Similar to Heidelberg, the CH mole fraction at 4 4 H 0 − mean [ppb] C 4

Schauinsland is lowest in summer, increases in au- c(−1000, −2000)

1950 H

tumn and decreases in spring. However, in win- −20 C c(HD_outputsampCH4$orig) ter the CH4 mole fraction at Schauinsland is lower 1900 again as the mountain station is often above the −40 boundary layer during this season. The orange data points show the mean mole fraction and iso- −47.4 topic composition of CH measured at Schauins- 0.2 4 c(HD_outputsampCH4$dezidate) c(1, 12) land during two measuring campaigns. The mean −47.6 0.1 CH4 mole fraction measured during these cam- paigns was lower than the mean of the correspond- −47.8

[‰] 0.0 13 4

ing months. However, the δ CH4 values follow H − mean [‰] C well the ones measured in Heidelberg. −48.0 4

13 −0.1 H δ c(−1000, −2000)

13 C The δ CH4 values at Heidelberg showed clearly 13

−48.2 −0.2 δ

more depleted values than in Mace Head. An offset c(HD_outputsampdCH4$orig) of 0.28 is subtracted from the MaceHead data −48.4 (Whiteh et al. 2018) to take into account the mea- −0.3 surement offsets among the laboratories INSTAAR and MPI-BGC (Umezawa et al. 2018). 2014 2015 2016 2017 2018 2019 2020 2 4 6 8 10 12 c(HD_outputsampdCH4$dezidate)year monthc(1, 12) * Dlugokencky et al. 2019 (https://doi.org/10.15138/VNCZ−M766), White et al. 2018 (ftp://aftp.cmdl.noaa.gov/data/trace_gases/ch4c13/flask/) EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 5 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt Diurnal cycle at Heidelberg and Schauinsland

diurnal cycle at Heidelberg (2014−2019) diurnal cycle at Schauinsland (2014−2019) The mean diurnal CH cycle in Heidelberg 4 40 DJF 2014 ± 7 ppb DJF shows a 10 times larger amplitude than at MAM 1985 ± 16 ppb MAM JJA 1958 ± 17 ppb 4 JJA the mountain station Schauinsland. The daily 30 SON 2013 ± 14 ppb SON variations of CH4 in Heidelberg show large 20 2 seasonal differences whereas the diurnal vari- 13 ations in δ CH4 are comparable during the 10 year. 0 0

At Schauinsland, no mean diurnal variation −mean [ppb] −mean [ppb] 4 4

13 H H can be noticed in δ CH for both measure- −10 −2

4 C C ment campaigns. −20 1947 ± 2 ppb The evaluation of the mean source signa- −4 1951 ± 2 ppb 1932 ± 1 ppb ture at Schauinsland is even more challeng- −30 1956 ± 2 ppb 0.15 ing than for Heidelberg due to the much lower 0 5 10 15 20 diurnal variability. hour 0.10 20 Feb/Mar campaign Sep/Oct campaign 15 0.05 10 5 0 −mean [ppb]

0.00 4 −5 1944.7 ± 3 ppb H −mean [‰] 1946.8 ± 6.9 ppb C 4 −10

H 0.3 −47.9 ± 0.1 ‰

C −0.05 0.2 −48.2 ± 0.1 ‰ 13

δ 0.1 −0.10 0.0

−48.1 ± 0.03 ‰ −mean [‰] −47.94 ± 0.04 ‰ 4 −0.1 −48.03 ± 0.06 ‰ H C −0.2 −48.27 ± 0.05 ‰ −0.15 13

δ −0.3 0 5 10 15 20 0 5 10 15 20 hour hour EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 6 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt Determination of the mean isotopic source signature

2017−09−29 2014−11−18 2015−01−24 In the Heidelberg CH4 record, we can identify three typical depen- 200 13 dencies of CH4 and δ CH4. 150 13 100 1.CH 4 increase and δ CH4 decrease (black) range [ppb] range → added CH4 is less enriched (e.g. dairy farms) 4 50 H

C 0 13 daten$CH4 − min(daten$CH4) daten$CH4 − min(daten$CH4) daten$CH4 − min(daten$CH4) 2.CH 4 increase and δ CH4 increase (blue) −45 → added CH is more enriched (e.g. natural gas facilities) −46 4 −47 daten$date daten$date daten$date [‰]

13 4 −48 3.CH 4 increase and δ CH4 constant (red) H −49 C

daten$dCH4 −50 daten$dCH4 daten$dCH4 → added CH4 is nearly the same than the background CH4 13 δ −51 However, in the last case, the added CH4 is most likely a gas mixture −52 of different sources. 20:00 00:00 04:00 08:00 22:00 02:00 12:00 16:00 20:00 timedaten$date [hh:mm] timedaten$date [hh:mm] timedaten$date [hh:mm] The precision of the isotopic source signature calculation using the Keeling or Miller-Tans approach strongly depends on the CH peak Miller−Tans approach Keeling approach 4 δ δ δ δ δ δ δ δ height and instrumental precision. Therefore, we use only Miller-Tans CH4obs· obs= S·CH4obs−CH4bg·( bg− S) obs= S+CH4bg·( bg− S)·1/CH4obs isotopic source signature −47.0 approach with CH4 enhancements larger than 50ppb. Different meth- −94000 −62.5 ± 1.7 ‰ −49.7 ± 2.1 ‰ −47.5 ods such as monthly/daily interval evaluations and moving Miller-Tans −39.6 ± 2.5 ‰ −96000 approaches (Rockmann¨ et al. 2016) have been used to calculate the −48.0 [ppb ‰] −98000 [‰] 4 isotopic source signature in ambient air. 4 H

NA −48.5NA H C −100000 C 13 13 −49.0 δ δ ·

4 −102000

H −49.5 −62.5 ± 1.7 ‰ C −104000 −49.7 ± 2.1 ‰ −50.0 −39.6 ± 2.5 ‰ 1950 2000 2050 2100 2150 2200 0.00051 0.00049 0.00047

CH4NA [ppb] −1 NA −1 CH4 [ppb ] EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 7 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt Mean isotopic source signature in Heidelberg

monthly Miller−Tans approach Miller−Tans approach of diurnal cycles moving MT (6,8,10 &12h intervalls We applied several methods to determine the York fit without fixed background isotopic CH4 source signature in Heidelberg. OLS fit with calc. background For panel a Miller-Tans approach is ap- −45 plied for each month. For the middle panel a Miller-Tans approach is used for each diur- −50

nal cycle. And on the right side moving Miller- NA NA NA Tans plots with time spans of 6,8,10 and 12h −55 were applied. For each of these three methods

(monthly, daily and moving) the isotopic signa- −60 tures are calculated in two different ways. First

we apply the York fit to the data without assum- monthly isotopic source signature [‰] 2015 2016 2017 2018 2019 2020 2015 2016 2017 2018 2019 2020 2015 2016 2017 2018 2019 2020 ing a background (black). The red data corre- yearNA yearNA yearNA sponds to isotopic source signatures calculated using a simple OLS fit with fixed intercept at monthly Miller−Tans approach Miller−Tans approach of diurnal cycles moving MT (6,8,10 &12h intervalls 0 and determined background data (mean of a −48 mean source signature mean source signature mean source signature (8&12h intervall) −54 ± 2 ‰ −53 ± 2 ‰ −52 ± 2 ‰ −53 ± 2 ‰ 48h interval using only daytime data). −54 ± 2 ‰ −53 ± 2 ‰ −52 ± 2 ‰ −53 ± 2 ‰ All methods show similar results. The monthly −50 isotopic methane source signatures of ambi-

ent air in Heidelberg was found to be between −52

-63 and -41 , with an average value of NA NA NA

(-53h± 2) . Anh annual cycle can be noticed −54 with moreh depleted values (-56 ) in summer

and more enriched values (-51h ) in winter. −56 This indicates a larger contributionh of biogenic monthly isotopic source signature [‰] sources in summer and thermogenic sources 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12

(e.g. natural gas) in winter. monthNA monthNA monthNA EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 8 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt Mean isotopic source signature at Schauinland

summer campaign winter campaign The mean isotopic source signature calcu- 2050 lated at Schauinsland shows variations, too, with more enriched values (-57 ) in winter 2000 [ppb]

and more depleted (-60 ) ones in autumn. 4 h 1950 H

The more depleted valuesh in summer/autumn C at Schauinsland correspond to more biogenic

1900AL_split_Data1min[[1]]$CH4 AL_split_Data1min[[2]]$CH4 methane and can be explained by dairy cows grazing near the station especially during this −44

time. −46 AL_split_Data1min[[1]]$date AL_split_Data1min[[2]]$date [‰] 4 −48 H C 13

δ −50

AL_split_Data1min[[1]]$dCH4 −52 AL_split_Data1min[[2]]$dCH4

Sep 21 Sep 25 Sep 29 Oct 03 Oct 07 Feb 18 Feb 23 Feb 28 Mar 05 Mar 10 Mar 15 Mar 20

AL_split_Data1min[[1]]$datedate 2019 AL_split_Data1min[[2]]$datedate 2018

−60.2 ± 0.7 ‰ −56.8 ± 0.4 ‰ −85000

−90000 [‰ ppb] 4

H −95000 C

4

H −100000 C 13 δ −105000Split2[[1]]$CH4 * Split2[[1]]$dCH4 Split2[[2]]$CH4 * Split2[[2]]$dCH4 1900 1950 2000 2050 1900 1950 2000 2050

Split2[[1]]$CH4CH4 [ppb] Split2[[2]]$CH4CH4 [ppb]

EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 9 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt Comparison with emission inventory of LUBW

Heidelberg (HD) The generally more enriched values at Mannheim (MA) Schauinsland are caused by the more ru- Rhein--Kreis (RNK) -Württemberg (BW) ral surrounding. Emission estimates of mean isotopic Freiburg im Breisgau (FR) counties provided by the Landesanstalt fur¨ IUP CH source signature Breisgau- Umwelt Baden-Wurttemberg¨ (LUBW) show 4 Hochschwarzwald (BH) HD: -50‰ that around Schauinsland 60% of the CH4 emissions are emitted by livestock farming MA: -49‰ -53‰ and around Heidelberg only 28%. RNK: -55‰ BW: -60‰ The mean isotopic composition of the CH4 FR: -50‰ emissions for Heidelberg and Schauinsland -58‰ are calculated using the inventory provided BH: -60‰ by the LUBW and isotopic source signatures measured for CH4 sources in the surround- ing (Hoheisel et al. 2019). The deter- methane emissions per section 100% mined mean isotopic source signature for Hei- natural gas delberg is (-53 ± 2) and for Schauinsland waste treatment 80% (-58 ± 2) . h old waste deposits These results agree well with the mean others 60% h other biogenic source signatures determined out of contin- livestock 40% uous isotopic measurements with values be-

tween -41 and -63 (mean -53 ± 2 ) for 20% Heidelbergh as well ash -57 and -61h for 0% Schauinsland. h h Schauinsland HD MA RNK BW FR BH (LUBW Landesanstalt für Umwelt Baden-Württemberg)

EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 10 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt Conclusion and Outlook

Conclusion

13 • the measured CH4 mole fraction and δ CH4 in Heidelberg show clear annual and diurnal variations

• the measured diurnal variations of the CH4 mole fraction at Schauinsland are much smaller, which made the determination of the mean source signatures more challenging than in Heidelberg 13 • the measured δ CH4 values at Schauinsland measured during two campaigns followed the seasonal cycle in Heidelberg • the mean isotopic source signature in Heidelberg shows an annual cycle with more enriched values in winter (-51 ) and more depleted ones in summer (-56 ). h • annualh source signatures calculated using county emission inventory provided by LUBW and determined signatures for different sources around Heidelberg (HD: -53±2 , SSL: -58±2 ) agree well with the values determined out of atmospheric measurements h h

Outlook • further improvement of the method and selection criteria to determine the mean isotopic source signature • analysis of wind pattern and trajectories • determination of mean isotopic source signature using MaceHead as background

EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 11 / 12 13 Continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany by A. Hoheisel, F. Meinhardt and M. Schmidt References & Acknowledgements

Dlugokencky, E. J., Myers, R. C., Lang, P. M., Masarie, K. A., Crotwell, A. M., Thoning, K. W., Hall, B. D., Elkins, J. W., and Steele, L. P.: Conversion of NOAA atmospheric dry air CH4 mole fractions to a gravimetrically prepared standard scale, J. Geophys. Res.-Atmos., 110, D18306, https://doi.org/10.1029/ 2005jd006035, 2005. Dlugokencky, E.J., A.M. Crotwell, J.W. Mund, M.J. Crotwell, and K.W. Thoning (2019), Atmospheric Methane Dry Air Mole Fractions from the NOAA ESRL Carbon Cycle Cooperative Global Air Sampling Network, 1983-2018, Version: 2019-07, https://doi.org/10.15138/VNCZ-M766 13 Hoheisel, A., Yeman, C., Dinger, F., Eckhardt, H., and Schmidt, M.: An improved method for mobile characterisation of δ CH4 source signatures and its application in Germany, Atmos. Meas. Tech., 12, 1123–1139, https://doi.org/10.5194/amt-12-1123-2019, 2019. Rockmann,¨ T., Eyer, S., van der Veen, C., Popa, M. E., Tuzson, B., Monteil, G., Houweling, S., Harris, E., Brunner, D., Fischer, H., Zazzeri, G., Lowry, D., Nisbet, E. G., Brand, W. A., Necki, J. M., Emmenegger, L., and Mohn, J.: In situ observations of the isotopic composition of methane at the Cabauw tall tower site, Atmos. Chem. Phys., 16, 10469–10487, https://doi.org/10.5194/acp-16-10469-2016, 2016. Sperlich, P., Uitslag, N. A. M., Richter, J. M., Rothe, M., Geilmann, H., van der Veen, C., Rockmann,¨ T., Blunier, T., and Brand, W. A.: Development and evaluation of a suite of isotope reference gases for methane in air, Atmos. Meas. Tech., 9, 3717–3737, https://doi.org/10.5194/amt-9-3717-2016, 2016. Umezawa, T., Brenninkmeijer, C. A. M., Rockmann,¨ T., van der Veen, C., Tyler, S. C., Fujita, R., Morimoto, S., Aoki, S., Sowers, T., Schmitt, J., Bock, M., Beck, J., Fischer, H., Michel, S. E., Vaughn, B. H., Miller, J. B., White, J. W. C., Brailsford, G., Schaefer, H., Sperlich, P., Brand, W. A., Rothe, M., Blunier, T., Lowry, D., 13 Fisher, R. E., Nisbet, E. G., Rice, A. L., Bergamaschi, P., Veidt, C., and Levin, I.: Interlaboratory comparison of δ C and δD measurements of atmospheric CH4 for combined use of data sets from different laboratories, Atmos. Meas. Tech., 11, 1207–1231, https://doi.org/10.5194/amt-11-1207-2018, 2018. White, J.W.C., B.H. Vaughn, and S.E. Michel (2018), University of Colorado, Institute of Arctic and Alpine Research (INSTAAR), Stable Isotopic Composition of Atmospheric Methane (13C) from the NOAA ESRL Carbon Cycle Cooperative Global Air Sampling Network, 1998-2017, Version: 2018-09-24, Path: ftp: //aftp.cmdl.noaa.gov/data/trace_gases/ch4c13/flask/

13 The authors thank Sylvia Michel for her help and supply of extra δ CH4 data from MaceHead which are not included in the ftp results. Special thanks to LUBW (Landesanstalt fur¨ Umwelt Baden-Wurttemberg)¨ for their help and providing county specific methane emission inventories. The CRDS analyser was funded through the DFG excellence initiative II. The data analysis of this study was funded by the Project 95297 with the German Environment Agency (UBA).

EGU 2020 Sharing Geoscience Online Session BG2.1 07.05.2020 12 / 12