Methane is a much more powerful greenhouse gas than carbon dioxide which captures much more heat. Point source methane emitters are usually small – usually less than 10 meters in diameter – but they emit very high concentrated methane. So if we want to reduce the amount of methane that we inject into the air (which we obviously should, even if we aren't), they would be big potential targets. If only we could identify them.
To map such point emissions, scientists in California flew across the state with an airborne imaging spectrometer and used it to measure methane emissions. They focused on a long list of potential sources: oil and gas production, processing, transmission, storage and distribution of equipment; refineries; milk manure locations; landfills and composting plants; wastewater treatment; gas-fired power plants; and liquidated and compressed natural gas plants.
Most of the facilities, especially dairies and oil fields, were located in the San Joaquin Valley. The researchers ended up measuring emissions from 564 different sources at 250 different plants. These point transmitters had not really been investigated before, as they often only extend their methane intermittently or in some sporadic way. To capture them, the researchers repeated flyovers five times between August 201
They conclude that about 40% of California's methane emissions come from these point source emitters rather than larger, more diffuse sources, such as rice fields. Over half of point emissions come from only 10% of sites.
The landfills were the worst, followed by dairies and the oil and gas sector. An earlier analysis that used atmospheric measurements rather than airborne image spectrometry reversed the relative charges from landfills and dairies, which led the authors to this more recent work which suggested that other emission sectors may also have been incorrectly estimated in the previous assessment. The authors also emphasize that, perhaps not shockingly, "Large differences are observed between many of the self-reported emissions from participating plants and [this airborne imaging study] and independent airborne estimates."
The good news is that when the researchers simply told plant operators that they had methane superemites, they could often reduce emissions. Four such cases were due to leaking liquid natural gas storage tanks; this study found the leaks and told the operators, who then repaired them. Further flyovers confirmed that the repairs stopped the emissions. This constant monitoring of both low-emission point transmitters and more widespread emissions can definitely help reduce methane emissions. Who could feed seaweed to cows.
Nature, 2019. DOI: 10.1038 / s41586-019-1720-3 (About DOIs).