Nitrogen dioxide over Europe on 22 November 2017.
Nitrogen dioxide over Europe on 22 November 2017. The highest concentrations are over the Po Valley in northern Italy and western Germany, likely associated with the combustion of fossil fuels from industry and road traffic. Credit: Contains modified Copernicus Sentinel data (2017), processed by KNMI/ESA

A new Earth-observing satellite called Sentinel-5P carries an advanced atmosphere-monitoring instrument that can scan Earth at a higher resolution than any other such instrument in orbit. The novel multispectral imaging spectrometer aboard the spacecraft, which is operated by the European Space Agency (ESA), reveals pollutants in our planet’s atmosphere with unprecedented granularity, according to the agency. Sentinel 5P can track gases such as nitrogen dioxide, ozone, formaldehyde, sulfur dioxide, methane, and carbon dioxide that are important to air quality and climate.

“These first images offer a tantalizing glimpse of what’s in store.”

Because of the spacecraft’s cutting-edge instrumentation and polar orbit, it is expected to provide daily global gas measurements at wavelengths ranging from the ultraviolet to shortwave infrared at a resolution as fine as 7 × 3.5 kilometers. This resolution provides at least 6 times more detail than previously available, commented Chris McLinden, a research scientist at Environment and Climate Change Canada in Toronto, Ontario.

“It’s like a switch from old TV to a new high-definition TV in terms of air quality measurements,” added McLinden’s colleague Vitali Fioletov, also of the Canadian agency.

Sentinel-5P’s new capabilities will allow scientists to track pollution emissions from individual cities and neighborhoods, ESA officials said during a briefing early this month at which a series of initial, or “first light,” images by the spacecraft was made public. “These first images offer a tantalizing glimpse of what’s in store,” said Josef Aschbacher, ESA’s director of Earth observation programs, during the event.

Artist’s concept of the Sentinel-5P satellite in orbit. Credit: ESA/ATG medialab

Heading to Full Operation

The initial images will allow scientists to verify and calibrate the spacecraft’s instruments as they continue to fully commission the spacecraft, which is expected to become fully operational a year from now. At that time, the satellite will release data about 3 hours after they are collected, according to ESA.

Sentinel-5P launched from Russia on 13 October after delays resulting from the complex political situation in Ukraine. After the satellite separated from its launch vehicle, ESA maneuvered it into its final orbit and brought it online in just 33 hours, a record for the agency, which usually needs 3 days for the process. Sentinel-5P started returning data on 8 November 2017, 2 weeks ahead of schedule.

Tracking Pollution from Above

The mission of the new satellite, the sixth in ESA’s Sentinel constellation, is to monitor air quality and climate by measuring atmospheric trace gases and aerosols as well as cloud distributions.

The mission of the new satellite, the sixth in ESA’s Sentinel constellation, is to monitor air quality and climate by measuring atmospheric trace gases and aerosols as well as cloud distributions.

Sentinel-5P isn’t the only satellite tracking air pollution, although no others do it as quickly, in as much detail, or for as many gases. The aging Ozone Monitoring Instrument on NASA’a Aura satellite measures many of the same gases as Sentinel but at a far coarser resolution and slower frequency. NASA’s Orbiting Carbon Observatory 2 continually measures atmospheric carbon.

With regard to the pollutant and greenhouse gas methane, “satellite observations have been scant,” explained McLinden in an email. Sentinel-5P, however, is expected to provide global methane monitoring by a satellite for the first time. That will allow researchers to link anthropogenic sources to their methane emissions, McLinden wrote, making the new satellite a “real game changer.”

Sentinel-5P steps up resolution but is also designed to provide global measurements of a wide range of gases repeated over the same geographical regions and at the same times of day. This repetition will make it easier to directly create multilevel maps of air quality, helping scientists to understand Earth’s complex systems and to inform policy makers about the impact of initiatives to improve air quality, ESA officials said.

Fioletov said that he hopes to make future use of the near-real-time data from Sentinel-5P in monitoring Canadian air quality. For power plants and other facilities that self-report emissions, “we can compare what those sources are reporting and what we can see from satellites,” he said. “[Then] we can see any discrepancies.”

McLinden noted that “we can resolve plumes of nitrogen dioxide and sulphur dioxide from larger natural and anthropogenic sources.” Sentinel-5P “will allow for monitoring at or near the sub-urban scale for the first time,” he said, adding that he sees potential for examining outgassing from the Canadian oil sands.

Carbon Monoxide

Sentinel-5P’s spectrometer measures a shortwave infrared channel that is new to the Sentinel constellation. This channel detects carbon monoxide, a gas produced by incomplete combustion.

In a video (below) of Sentinel-5P global carbon monoxide observations, the Northern and Southern Hemispheres show striking differences. High concentrations in the Northern Hemisphere reflect greater industrialization. Hot spots in Amazonia, Africa, and Madagascar stem from biomass burning, with prevailing winds carrying the polluted air into the Atlantic Ocean, ESA scientists explained at the 1 December 2017 briefing. Additional hot spots over China and India indicate both fires and industrial activity, with a pollution plume from China blowing into the Pacific Ocean.

Global carbon monoxide levels recorded by Sentinel-5P from 9 to 22 November 2017. Credit: SRON/ESA

Observing Volcanoes

Because of Sentinel-5P’s ability to detect aerosols, the satellite can also monitor volcanic eruptions and the abundant sulfur dioxide gas that they release. The higher resolution of Sentinel-5P means that scientists will be able to detect sulfur dioxide levels with more detail than previously possible, resolving wispy trails of the gas from eruptions that would be seen as pixelated blurs by less sensitive instruments, Fioletov explained.

Sulfur dioxide (SO2) from the eruption of Mount Agung on Bali, Indonesia, detected by the new satellite on 27 November 2017. Credit: ESA/DLR

During the first-light data collection in November, the satellite spied eruptions from Mount Etna in Italy, Mount Agung in Bali, and Ambae in Vanuatu. Fossil fuel–burning power plants, ships, heavy vehicles, and industrial facilities like those that process metal ores also emit sulfur dioxide.

—Mika McKinnon (email:, Freelance Science Journalist


McKinnon, M. (2017), Advanced satellite tracks air pollution in extraordinary detail, Eos, 98, Published on 18 December 2017.

Text © 2017. The authors. CC BY-NC-ND 3.0
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