Quantifying urban methane emissions in the city of Stuttgart
Authors: Nelson Carolina , Schmidt Martina , Butz André , Roiger Anke 
Published: March 2020

&lt;p&gt;Even if methane (CH&lt;sub&gt;4&lt;/sub&gt;) is one of the most important anthropogenic greenhouse gases, its sources in urban areas are quantitatively highly uncertain. Plant et al. (2019) highlights that current urban inventories probably substantially underestimate real methane emissions. Bottom-up estimates from the German Environmental Agency show uncertainties in urban sources even higher than 300 % (LUBW 2014). Yet for decision makers it is essential to know the strength of potential sources in order to prioritise and perform mitigation actions.&lt;/p&gt;&lt;p&gt;Baden-W&amp;#252;rttemberg is amongst the regions with the highest estimated methane emission in Germany[i]. Its capital town Stuttgart with more than 600.000 inhabitants is not only the biggest town but also an important industrial centre of the region. As the city centre is located in a deep circular valley the geographical conditions of Stuttgart favour high air pollution and emission stresses. Therefore, the need of emission reduction is strong and of high political interest. Using the example of Stuttgart, this work empirically targets the gap of knowledge about urban methane emission to provide a scientific base for effective local policy measures. More precisely, this study aims to exemplarily quantify typical urban source like waste water treatment plants and natural gas distribution and storage systems in the city of Stuttgart, Germany, by drive-by in-situ measurements and applied plume diffusion models.&lt;/p&gt;&lt;p&gt;Within this study, two optical instruments are used in a mobile setup in a van to measure CH&lt;sub&gt;4&lt;/sub&gt;, CO&lt;sub&gt;2&lt;/sub&gt;, H&lt;sub&gt;2&lt;/sub&gt;O, Ethane and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;CH&lt;sub&gt;4&lt;/sub&gt; isotopes: a cavity ring-down spectrometer (CRDS, Picarro G2201-I) and Trace Gas Analyzer (OF-CEAS, LiCor LI-7810). Simultaneous 2D wind data and recorded weather conditions allow the application of dispersion models. Our research group used this technique and successfully tested a gaussian plume model on rural sources like dairy farms around Heidelberg, Germany. With the help of the isotopic composition and the Ethane concentrations, thermogenic sources and biogenic sources can be differentiated.&lt;/p&gt;&lt;p&gt;In August and December 2019, two short campaigns have been performed to identify potentially big sources in Stuttgart. The wastewater treatment plant in M&amp;#252;hlhausen and the natural gas storage facility in Gaisberg have been selected as representative targets. A next campaign is planned in spring 2020, including probably 3D-wind measurements and elaborated dispersion models. By taking advantage of inversion weather conditions, which are typical for Stuttgart, mass balance models can possibly be applied. So far, the results promise to allow quantifying emission rates of the target sources.&lt;/p&gt;&lt;div&gt;
&lt;p&gt;&lt;em&gt;LUBW 2014: Luftschadstoff-Emissionskataster Baden-W&amp;#252;rttemberg 2014, Landesanstalt f&amp;#252;r Umwelt, Messungen und Naturschutz Baden-W&amp;#252;rttemberg (LUBW)&lt;/em&gt;&lt;/p&gt;
&lt;p&gt;&lt;em&gt;Plant et al. 2019: Large Fugitive Methane Emissions From Urban Center Along the U.S. East Coast, Genevieve Plant, Eric A. Kort, Cody Floerchinger, Alexander Gvakharia, Isaac Vimont and Colm Sweeney, Geophysical Research Letters 2019&lt;/em&gt;&lt;/p&gt;
[i] https://www.statistikportal.de/de/ugrdl/ergebnisse/gase/ch4
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