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

Methane (CH4) plays a crucial role in the Earths’ radiative balance, since it
is a potent greenhouse gas with a shorter lifetime compared to CO2. Mitigating
methane emissions could help mitigate climate change in a short time frame.
This requires a solid understanding of the emissions on the location, strength and
the type of the source. Isotopic analysis can help with the source partitioning
since different sources emit CH4 with slight but significant differences in the
isotopic 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 by
deployment of this system in Cluj-Napoca. The goal is to investigate the typical
source mix of methane in this region and investigate whether the observations
agree with emission inventories. This data is combined with a mobile surveys
to investigate suspected sources.
The work performed on the continuous data-series indicate that the night
time accumulation has an important role in the mixing ratio and the signatures
of both the δD and δ13C. Furthermore it suggest that the enhancements can be
explained by a combination of leakages from the gas network, combined with
microbial sources. Wind directions indicates that the city centre has significant
contributions to these emissions.