Methane mapping, emission quantification, and attribution in two European cities: Utrecht (NL) and Hamburg (DE)

Abstract

Abstract. Characterizing and attributing methane (CH4) emissions across varying scales are important from environmental, safety, and economic perspectives and are essential for designing and evaluating effective mitigation strategies. Mobile real-time measurements of CH4 in ambient air offer a fast and effective method to identify and quantify local CH4 emissions in urban areas. We carried out extensive campaigns to measure CH4 mole fractions at the street level in Utrecht, the Netherlands (2018 and 2019), and Hamburg, Germany (2018). We detected 145 leak indications (LIs; i.e., CH4 enhancements of more than 10 % above background levels) in Hamburg and 81 LIs in Utrecht. Measurements of the ethane-to-methane ratio (C2:C1), methane-to-carbon dioxide ratio (CH4:CO2), and CH4 isotope composition (δ13C and δD) show that in Hamburg about 1∕3 of the LIs, and in Utrecht 2∕3 of the LIs (based on a limited set of C2:C1 measurements), were of fossil fuel origin. We find that in both cities the largest emission rates in the identified LI distribution are from fossil fuel sources. In Hamburg, the lower emission rates in the identified LI distribution are often associated with biogenic characteristics or (partly) combustion. Extrapolation of detected LI rates along the roads driven to the gas distribution pipes in the entire road network yields total emissions from sources that can be quantified in the street-level surveys of 440±70 t yr−1 from all sources in Hamburg and 150±50 t yr−1 for Utrecht. In Hamburg, C2:C1, CH4:CO2, and isotope-based source attributions show that 50 %–80 % of all emissions originate from the natural gas distribution network; in Utrecht more limited attribution indicates that 70 %–90 % of the emissions are of fossil origin. Our results confirm previous observations that a few large LIs, creating a heavy tail, are responsible for a significant proportion of fossil CH4 emissions. In Utrecht, 1∕3 of total emissions originated from one LI and in Hamburg >1/4 from two LIs. The largest leaks were located and fixed quickly by GasNetz Hamburg once the LIs were shared, but 80 % of the (smaller) LIs attributed to the fossil category could not be detected and/or confirmed as pipeline leaks. This issue requires further investigation.

Measurement report: Methane (CH<sub>4</sub>) sources in Krakow, Poland: insights from isotope analysis

“…Gas migrating in the distribution network can undergo secondary processes such as oxidation, that influence the isotopic signatures, usually towards more enriched values. Isotopic variations among network gas leaks were also observed previously in other cities (Zazzeri et al (2017), Maazallahi et al (2020), Defratyka et al (2021)).…”

“…This is also true for emissions from the natural gas network, confirming their fossil fuel origin. In the USCB region, δ 2 H signatures seem to be more suitable than δ 13 C values for source apportionment, similar to recent studies made in European cities (in Hamburg byMaazallahi et al, 2020, and in Bucharest by Fernandez et al, 2021)…”

Methane (CH<sub>4</sub>) sources in Krakow, Poland: insights from isotope analysis

“…Time series of δ 13 C-CH 4 and δ 2 H-CH 4 were generated from simulated CH 4 mole fractions using the CHIMERE atmospheric transport model (Menut et al, 2013;Mailler et al, 2017), driven by the PYVAR system (Fortems-Cheiney et al, 2019). CHIMERE is a three-dimensional Eulerian limitedarea chemistry-transport model for the simulation of regional atmospheric concentrations of gas-phase and aerosol species.…”

Isotopic Signatures of Major Methane Sources in the Coal Seam Gas Fields and Adjacent Agricultural Districts, Queensland, Australia

“…However, many sources of greenhouse gases have a characteristic isotopic signature, which can be used for source attribution when used in conjunction with other insights. While ethane measurements have been used previously to distinguish methane (CH4) plumes from oil and gas activities vs. agricultural and other sources (e.g., Maazallahi et al, 2020;Mielke-Maday et al, 2019;Smith et al, 2015), the low ethane content in Australian coal seam gas (Hamilton et al, 2012;Sherwood et al, 2017) renders the use of ethane measurements for source attribution impractical. This research sought to characterise isotopic signatures and to discriminate sources of CH4 in the Surat Basin.…”