Continuous monitoring of the isotopic composition of methane in Cluj-Napoca.

Methane (CH4) plays a crucial role in the Earths’ radiative balance, since itis a potent greenhouse gas with a shorter lifetime compared to CO2. Mitigatingmethane emissions could help mitigate climate change in a short time frame.This requires a solid understanding of the emissions on the location, strength andthe type of the source. Isotopic analysis can help with the source partitioningsince different sources emit CH4 with slight but significant differences in theisotopic composition.Utrecht University developed an isotope ratio mass spectrometer (IRMS)system capable of measuring δ13C and δD of CH4 at high precision with ap-proximately hourly time resolution for both isotope signatures. Under the Hori-zon Europe project PARIS (Process Attribution of Regional Emissions) we ex-panded the coverage of high time resolution isotope measurements in Europe bydeployment of this system in Cluj-Napoca. The goal is to investigate the typicalsource mix of methane in this region and investigate whether the observationsagree with emission inventories. This data is combined with a mobile surveysto investigate suspected sources.The work performed on the continuous data-series indicate that the nighttime accumulation has an important role in the mixing ratio and the signaturesof both the δD and δ13C. Furthermore it suggest that the enhancements can beexplained by a combination of leakages from the gas network, combined withmicrobial sources. Wind directions indicates that the city centre has significantcontributions to these emissions.