Intercomparison of detection and quantification methods for methane emissions from the natural gas distribution network in Hamburg, Germany

Abstract

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.

Intercomparison of detection and quantification methods for methane emissions from the natural gas distribution network in Hamburg, Germany

“…Data availability. The mobile and tracer release datasets are available on the Integrated Carbon Observation System (ICOS) portal from Maazallahi et al (2023a).…”

“…Video supplement. A virtual tour of the measurements is available on the Leibniz Information Centre for Science and Technology and University Library (TIB) portal from Maazallahi et al (2023b).…”

High-resolution modelling of plume dispersion

“…Our aim for this study is to assess source strength estimation methods from street level measurements using DNS. The measurement strategy we are focusing on was first developed by Weller et al (2019) and has recently been used to detect and estimate fugitive methane emissions (Maazallahi et al, 2020(Maazallahi et al, , 2022. To the best of our knowledge, this estimation method has not yet been systematically tested for the influence of the atmospheric parameters on the plume variability and consequently the source estimations.…”

“…We therefore use DNS to simulate dispersion from multiple scalar sources in a MUST set-up. This study is inspired by the measurement campaign of city methane emissions conducted in Hamburg, Germany (Maazallahi et al, 2022). As a first step, we limit this study to dispersion under neutral atmospheric conditions and with the mean wind direction aligned with the street as we expect that the estimation method performs best for this geometry.…”

“…This chapter is structured as follows: In section 6.2 we shortly describe the Weller method as it is the main focus of this study. Section 6.3 describes one of the residential streets in Hamburg in which Maazallahi et al (2022) detected methane leaks and which we used to construct an idealized MUST. The numerical model and the numerical experiment set-up are described in section 6.4.…”