13 Evaluation of continuous δ CH4 measurements in Heidelberg and at Schauinsland, Germany Antje Hoheisel1, Frank Meinhardt2, Martina Schmidt1 (1) Institute of Environmental Physics, Heidelberg University, 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 Odenwald G2201-i analyser has been used to continuously measure CH 4 industrial cities Mannheim and Ludwigshafen 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 Rhine 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 Freiburg im Breisgau fraction is measured since 1992. Schauinsland is on the edge Schauinsland of the black forest to the Rhine valley, south-east of the city Freiburg im Breisgau. 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 Jena (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 au- 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.