the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Intercomparison of detection and quantification methods for methane emissions from the natural gas distribution network in Hamburg, Germany
- 1Institute for Marine and Atmospheric research Utrecht (IMAU), Utrecht University (UU), Utrecht, The Netherlands
- 2Netherlands Organisation for Applied Scientific Research (TNO), Utrecht, the Netherlands
- 3Department of Environmental Engineering, Technical University of Denmark (DTU), Lyngby, Denmark
- 4Environmental Defense Fund (EDF), Berlin, Germany
- 1Institute for Marine and Atmospheric research Utrecht (IMAU), Utrecht University (UU), Utrecht, The Netherlands
- 2Netherlands Organisation for Applied Scientific Research (TNO), Utrecht, the Netherlands
- 3Department of Environmental Engineering, Technical University of Denmark (DTU), Lyngby, Denmark
- 4Environmental Defense Fund (EDF), Berlin, Germany
Abstract. In August and September 2020, three different measurement methods for quantifying methane (CH4) emission from leaks in urban gas distribution networks were applied and compared in Hamburg, Germany: the “mobile”, “tracer release” and “suction” methods. The mobile and tracer release methods determine emission rates to the atmosphere from measurements of CH4 mole fractions in the ambient air, and the tracer release method also includes measurement of a gaseous tracer. The suction method determines emission rates by pumping air out of the ground using soil probes that are placed above the suspected leak location. The quantitative intercomparison of the emission rates from the three methods at a small number of locations is challenging because of limitations of the different methods at different types of leak locations.
The mobile method was designed to rapidly quantify the average or total emission rate of many gas leaks in a city, but it yields a large emission rate uncertainty for individual leak locations. Emission rates determined for individual leak locations with the tracer release technique are more precise because the simultaneous measurement of the tracer released at a known rate at the emission source eliminates many of the uncertainties encountered with the mobile method. Nevertheless, care must be taken to properly collocate the tracer release and the leak emission points to avoid biases in emission rate estimates. The suction method could not be completed or applied at locations with widespread subsurface CH4 accumulation, or due to safety measures, and this sampling bias may be associated with a bias towards leak locations with low emission rates. The leak locations where the suction method could not be applied were the biggest emitters as confirmed by the emission rate quantifications using mobile and tracer methods and an engineering method based on leak’s diameter, pipeline overpressure and depth at which the pipeline is buried. The corresponding sampling bias for the suction technique led to a low bias in derived emission rates in this study. It is important that future studies using the suction method account for any leaks not quantifiable with this method in order to avoid biases, especially when used to inform emission inventories.
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Hossein Maazallahi et al.
Status: final response (author comments only)
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RC1: 'Comment on amt-2022-134', Anonymous Referee #1, 17 May 2022
- In line 333, are the equation 3 taking into account the meteorological factors? If not, please evaluate the impact of meteorological data on the final results.
- Whether the large distribution of the maximum enhancement mentioned in lines 471-473 will affect the judgment of the threshold, and thus affect the results
- Are the values of relative uncertainty mentioned in lines 479~486 too large and Whether they will affect the overall degree of confidence of the data
- What is the cause in lines 756-760 that the emission rates of the locations provided by the LDC were much lower than the locations detected by mobile measurements
- About The two C2H6 signals mentioned in lines 789~794 that are not confirmed as the location of leakage by LDC, you suggest two reasons that they are related to the distant leakage and transmission, or surrounding emission sources. For the first reason, Is it possible to compare the wind speed and direction when C2H6 signals are measured to find the location of leakage, For the latter reason, can you match the signal with the sources may produce both CH4 and C2H6.
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CC1: 'Comment on amt-2022-134', Luise Westphal, 13 Jun 2022
This is a joint comment. On the one hand of the scientists around the suction method. On the other hand of the network operator (Gasnetz Hamburg) which supported the method comparison with network plans, employees and gas detection technology. The method comparison was limited to a few measurement points, but a successful exchange of knowledge about the measurement systems. We do not agree on all points, so we have taken these up in the comments and presented our view.
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RC2: 'Comment on amt-2022-134', Anonymous Referee #2, 07 Aug 2022
The quantification of CH4 emissions from gas leaks is highly important and an interesting dataset has been obtained using different methods. While parts of the manuscript are well written and also interesting conclusions have been drawn, other parts need major improvements. In my opinion, this paper can only be published after these improvements have been made and a reviewer (ideally from the inventory community) has seen the revised paper. The suggested improvements are mainly concerning the suction method and its implications on the inventories.
1) Line 135-136: “The reported uncertainty range of this method is ± 10% based on 23 measurements in the 1990s (E.ON, personal communication, 2020).”
This is only an appropriate reference if there is no published data about the uncertainty of the suction method. In this case, it should be stated that to your knowledge there are no publications about the uncertainty of the suction method. Otherwise, an appropriate reference should be used.
2) Line 518-524: “At several of the locations where the mobile method had indicated high emission rates subsurface accumulation was widespread, and the suction method was either not deployed or the measurements were incomplete because of either safety reasons or because the suction team estimated that they would be unable to complete the measurements within a day.”
I do not understand the requirement to complete the measurements within a day. If the aim of the study is to compare methods, the measurements should be completed even if it takes longer than a day. This constraint resulted in only one data point (fully completed measurement) for the suction method. In line 1002-1003 it is stated “While the mobile and tracer methods have been evaluated previously, this is the first peer-reviewed study that includes the suction method.” I doubt that one can state this given just one completed measurement. It could be justified if the partially completed sampling and its comparison to the other methods is discussed in more detail
3) Line 960-997 “4.4 Possible suction method sampling bias with implications for emission inventories”
After reading it the first time I became interested in the topic and started reading the referenced reports. After doing this, my conclusion is that 4.4. needs major revision.
You write in line 961-962 “The national inventory for CH4 leakage from the gas distribution network in Germany is based on measurements with the suction technique (Umweltbundesamt, 2021).” I wanted to find out to which degree the inventory is based on the suction method and had a look at the referenced report. What I found is a reference to Gottwald et al., 2012 and Müller-Syring & Schutz, 2014. I had only a look at the latter reference and this only discusses theoretical emission estimates. It could be my fault that I missed the appropriate section in this extended report. However, it would be good to clarify what is meant with “based on” and it would be good to state where in this very extended report this can be found. (similar to what you do in line 966)
The next reference I was looking at was “MEEM 2022” (line 963). According to the reference section this is “MEEM, Analysing the Methods for Determination of Methane Emissions of the Gas Distribution Grid (2022). [online] Available from https://www.dbi-gut.de/emissions.html. (Last Accessed: 25 January 2022)” The link refers to a webpage of a project and the “MEEM Project - Phase I” has the title as given in the stated reference. I only found a “Management Summary GERG Project Phase I with the title Analysing the Methods for Determination of MethaneEmissions of the Gas Distribution Grid” published in May 2016. The second phase under a different name has been completed in 2018. Therefore the reference to the “ongoing project”, which is “underway to refine these emission estimates” needs to be updated.
Line 965-966: “This implies that this method is not applied at locations of the A1 category, which demand immediate repair (P. 27 in GERG, 2018).” Though the statement is correct in Annex 5 of the given reference it is stated “Three measurement principles are considered for direct measurements on underground pipelines: Tracer Method, Suction Method, High Flow Sampler”. Though I see that the suction method could “have a location sampling bias towards leaks in the B and C category”, I am not convinced that it is not accounted for this bias in the inventories by using other methods for the A1 and A2 categories.
In summary: I think this section is interesting but needs to be re-written. The references of the reports should be revised (correct year, link,...), Also, the reference GERG, 2018 and GERG 2020 are the same. In addition, it needs to be clearer what the suction method is used for and if this has really implications for the emission inventories or not.
Hossein Maazallahi et al.
Data sets
Mobile and tracer measurements Maazallahi, H., Delre, A., Scheutz, C., Fredenslund, A. M., Schwietzke, S., Denier van der Gon, H., Röckmann, T. https://fileshare.icos-cp.eu/s/wTjBngNKfCBi2PL
Hossein Maazallahi et al.
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