Potential Sources of Methane Emissions in Urban Areas

Methane, a potent greenhouse gas with a relatively short atmospheric lifetime and the potential for rapid, targeted abatement, is gaining importance for near-term climate action.

Despite that Urban Areas cover <2% of the Earth’s surface, they are responsible for either anthropogenic or natural a large fraction of CH₄ emissions from different types of sources. Urban Areas are responsible for a large fraction of GHG emissions (30 to 40% of global anthropogenic emissions), including methane from the different types of sources.

Usually, urban studies are generally focused on gas leaks from natural gas networks, domestic networks, combustion systems, landfills, wastewater (sewer systems) and road transport.

However, CH₄ emissions have a high degree of uncertainty and aquatic systems in Urban Areas are generally neglected in the literature. Also, the Romanian national GHG inventory does not report Urban Areas emissions of CH₄.

Our study is a preliminary identification of urban sources for CH₄ emissions in Cluj-Napoca, the second most populous city in Romania, based on a simple detection of gas leaks, CH₄ content in aquatic systems.

Tunable Diode Laser Absorption Spectroscopy (TDLAS) with resolution of 0.1 ppmv were used to determine the atmospheric concentrations of gas at different points of potential sources of CH₄ around the city. Also, gas from water samples was analyzed via head-space extraction and the CH4 laser sensor of TDLAS.

This study has revealed that more than 76% of the natural gas distribution points and more than 39% sewer man-holes have values higher than the estimated background. All water samples are almost over-saturated with CH₄, which means that the aquatic ecosystems represent a potential source of CH₄ fluxes into the atmosphere.

These results indicate that flux measurements and sources attribution of CH₄ are required for further investigation of all CH₄-bearing systems.