【気候科学】米国カリフォルニア州内のメタンの超大量排出源を特定する

A third of California’s methane output in 2016 came from localized single sources, with only ten per cent of these so-called point sources (less than ten metres in diameter) contributing to 60 per cent of the total point source emissions, reports a paper published this week in Nature. Some mitigation of methane emissions has already been achieved after preliminary data was shared with the super-emitters.

Reducing highly concentrated methane emissions from small surface features or infrastructure components, such as landfill sites or oil- and natural-gas-processing facilities, can help mitigate climate change. To monitor point-source emissions in California, Riley Duren and colleagues surveyed over 272,000 infrastructure elements using an airborne spectrometer capable of rapidly mapping methane plumes. They conducted five campaigns over several months from 2016 to 2018, spanning the manure- and waste-management and oil and gas sectors. This resulted in the detection, geolocation and quantification of 564 strong methane point sources. The authors found that landfills make the largest contribution to methane point-source emissions, followed by dairies and the oil and gas sector.

Sharing the observations with collaborating facility operators directly led to mitigation of the methane sources detected by the survey, the authors note. For example, leaks in gas lines and storage tanks were fixed after being discovered by the researchers.