18 Nov 2022
18 Nov 2022
Status: this preprint is currently under review for the journal ACP.

Quantification of methane emissions in Hamburg using a network of FTIR spectrometers and an inverse modeling approach

Andreas Forstmaier1, Jia Chen1, Florian Dietrich1, Juan Bettinelli1, Hossein Maazallahi2,5, Carsten Schneider2,4, Dominik Winkler1, Xinxu Zhao1, Taylor Jones6, Carina van der Veen2, Norman Wildmann3, Moritz Makowski1, Aydin Uzun1, Friedrich Klappenbach1, Hugo Denier van der Gon5, Stefan Schwietzke7, and Thomas Röckmann2 Andreas Forstmaier et al.
  • 1Environmental Sensing and Modeling, Technical University of Munich (TUM), Munich, Germany
  • 2Institute for Marine and Atmospheric research Utrecht (IMAU), Utrecht University (UU), Utrecht, the Netherlands
  • 3Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 4Institut für Umweltphysik, University of Heidelberg, Heidelberg, Germany
  • 5Netherlands Organisation for Applied Scientific Research (TNO), Utrecht, the Netherlands
  • 6Earth and Environment, Boston University, Boston, United States
  • 7Environmental Defense Fund, Berlin, Germany

Abstract. Methane (CH4) is a potent greenhouse gas and anthropogenic CH4 emissions contribute significantly to global warming. In this study the CH4 emissions of the city of Hamburg, Germany were quantified with measurements from four solar-viewing Fourier Transform Infrared Spectrometers (FTIR), mobile in-situ measurements and an inversion framework. For source type attribution an Isotope Ratio Mass Spectrometer was deployed in the city. The urban district hosts an extensive industrial and port area in the south, as well as a large conglomerate of residential areas north of the Elbe river. For emission modeling the TNO GHGco inventory was used as a basis. In order to improve the inventory, two approaches were followed: Firstly the addition of a large natural CH4 source, the Elbe river, which was previously not in the inventory. Secondly mobile measurements were carried out to update the spatial distribution of emissions in the TNO GHGco gridded inventory and derive two updated versions of the inventory. The addition of the river emissions improved model performance, while the correction of the spatial distribution with mobile measurements did not have a significant effect on the total emission estimates for the campaign period. A comparison of the updated inventories with emission estimates from a Gaussian Plume Model (GPM) showed that the updated versions of the inventory in several cases match the GPM emissions estimates well, highlighting the potential of mobile measurements to derive up-to-date emission inventories. The mobile measurement survey also revealed a large, so far unknown point source of fossil origin with a magnitude of 0.069 ± 0.047 Gg/yr. The isotopic measurements show strong indications that there is a large biogenic CH4 source in Hamburg which produced repeated enhancements of over 1ppm. The CH4 emissions (anthropogenic and natural) of the city of Hamburg were quantified as 14 ± Gg/yr of which 7.9 ± 4.4 Gg/yr are of anthropogenic origin. This study reveals that mobile measurements at street-level may miss the majority of total methane emissions, potentially due to sources within buildings including stoves and boilers operating on fossil gas (also referred to as "natural gas"), as well as due to large area sources like for instance the Alster lake.

Andreas Forstmaier et al.

Status: open (until 30 Dec 2022)

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Andreas Forstmaier et al.

Andreas Forstmaier et al.


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Short summary
Large cities emit greenhouse gases which contribute to global warming. In this study we measured the release of one important green house gas, methane in the Hamburg. Multiple sources that contribute to the methane emissions were located and quantified. Methane sources were found to be mainly caused by human activity, for example by the release from oil and gas refineries. Also potential natural sources have been located such as the Elbe river and lakes.