The plume shown in this photo from NASA’s EMIT (Earth Surface Mineral Dust Source Investigation) instrument comes from an Iranian landfill that’s spewing about five tons of methane per hour into the atmosphere. Point sources from waste-management sites and from oil and gas operations contribute more than 30% of humankind’s total methane emissions.
Despite the magnitude of such emissions, there’s still a lot of uncertainty about where they’re coming from. Many countries, for example, lack continuous monitoring and reporting programs, which make bottom-up inventories difficult. Most remote-sensing instruments on satellites either have fine spatial resolution or cover a broad area—but not both. The same issues stymie efforts to accurately estimate carbon dioxide emissions.
Attached to the International Space Station, EMIT solves some of those problems. Its two-mirror telescope focuses incoming light on an imaging spectrometer, which measures reflected solar radiation in the visible to shortwave-IR wavelengths that greenhouse gases absorb. With a higher signal-to-noise ratio than similar spectrometers, the instrument has a spatial resolution of 60 m. It can cover most of Earth’s surface, from 51.6° N to 51.6° S, and observes a large area per day, about 1.3 million km2—roughly the size of Peru. And given the orbit of the space station, EMIT also offers some temporal coverage, with an average of 10 visits to a location each year.
The plumes observed with EMIT over its first month of operation in July–August 2022 combined with other data—the mass of carbon dioxide and methane, the plume lengths, and wind speeds—were used to estimate emissions at 126 point sources. During their analysis, Andrew Thorpe of NASA’s Jet Propulsion Laboratory in Pasadena, California, and colleagues also located other superemitters: power plants in China releasing CO2 and individual point sources in oil fields in Saudi Arabia and Turkmenistan emitting methane. EMIT’s primary mission ends later this month, but NASA has requested an extension to observe additional greenhouse gases. Since the launch, the instrument has measured more than 800 methane point sources. (A. K. Thorpe et al., Sci. Adv. 9, eadh2391, 2023.)