TROPOMI detects urban methane emissions associated with untreated wastewater


Recorded on June 1, 2023

Even though methane concentrations have contributed an estimated 23% of climate forcing, part of the recent increases in the global methane background concentrations remain unexplained. Satellite remote sensing has been used extensively to constrain emission inventories, for example with the TROPOspheric Monitoring Instrument (TROPOMI) which has been measuring methane since November 2017. We have identified enhancements of methane over 61 urban areas around the world and estimate their emissions using a two-dimensional Gaussian model. We show that methane emissions from urban areas may be underestimated by a factor of 3 to 4 in the EDGAR greenhouse gas emission inventory. Scaling our results to the 385 urban areas with more than 2 million inhabitants suggests that they could account for up to 22% of global methane emissions. The emission estimates of the 61 urban areas do not correlate with the total or sectoral EDGAR emission inventory. They do however correlate with estimated rates of untreated wastewater, varying from 33 kg person(-1) year(-1) for cities with zero untreated wastewater to 138 kg person(-1) year(-1) for the cities with the most untreated wastewater. If this relationship were confirmed by higher resolution remote sensing or in situ monitoring, we estimate that reducing discharges of untreated wastewater could reduce global methane emissions by up to 5 to 10% while at the same time yielding significant ecological and human co-benefits.

Dr. de Foy is an atmospheric scientist whose research focuses on data mining and computer modeling of air pollution. After a PhD in engineering from Cambridge University he worked with Dr. Mario Molina at the Massachusetts Institute of Technology on a project to improve the air quality in Mexico City. He is the Banpu Chair in Sustainability at Saint Louis University where he researches air pollution in places ranging from East St. Louis to Tibet. He works extensively with satellite remote sensing of air quality around the globe. He developed the oversampling method to identify pollution sources impacting Mexico City using OMI retrievals and has quantified individual points sources within urban areas using TROPOMI to improve emission inventories. His latest collaboration is on a project to analyze data from hundreds of air quality monitors deployed in cities and rural areas in seven countries in South Asia.

You can find information at his website:


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