A European spacecraft launched in October 2017 provides data on worldwide tropospheric pollution to a finer degree than ever before, even though it’s not yet fully operational. Part of the European Space Agency’s (ESA) Copernicus Earth Observation programme, the Sentinel 5 Precursor (S5P) carries the Dutch-built TROPOspheric Monitoring Instrument (TROPOMI), a four-band spectrometer.

S5P flies in a near polar orbit at an altitude of 824 km; it scans the entire globe each day. The principal investigator for TROPOMI, Pepijn Veefkind of the Royal Netherlands Meteorological Institute (KNMI), presented maps pinpointing the source of several important pollutants, as identified by TROPOMI, to journalists at the American Geophysical Union’s (AGU) Fall Meeting in December in Washington, DC.

Nitrogen dioxide (NO2) is produced, for example, by power plants and forest fires, but has a lifetime of only a day. “There is more detailed information than we ever had” on the specific location of NO2 emissions, thanks to the daily fly-bys and high resolution of TROPOMI images, Veefkind said. “You can go from the global view, zoom all the way in to the urban regions”, which is what the instrument was designed to do.

Veefkind showed a NASA Suomi-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) image of a massive smoke plume, several hundred kilometres long, from the Camp Fire that obliterated Paradise, California, starting on November 8, 2018. He overlaid NO2 data from TROPOMI, collected just five minutes later, onto the VIIRS image, to show that the fire was extremely hot and that the biomass was burning incompletely.

Carbon monoxide (CO) is produced by incomplete burning, especially of biomass, such as by wildfires, Veefkind said, and is well tracked by TROPOMI. CO lives longer than NO2, so its plume can be traced from source regions through the entire hemisphere for the first time. Its presence is strong in TROPOMI images of the Camp Fire. Similarly, TROPOMI also revealed that the carcinogenic pollutant formaldehyde (HCHO) was strongly present in the fire’s plume.

In the future TROPOMI will provide detailed information on the formation of tropospheric methane (CH4), a powerful greenhouse gas. It will rely on VIIRS images to find areas that are completely cloud-free, a necessity for accurate methane tracking.

S5P flies in almost the same polar orbit as NASA’s Suomi NPP, which was launched in 2011. Designed to work in tandem with the NASA satellite, S5P passes over each spot on Earth five minutes later. The VIIRS hyperspectral instrument, although an older technology with lower resolution than TROPOMI, covers a similar swath on Earth’s surface, said Barry Lefer, program manager of NASA’s tropospheric composition programme. ESA’s Claus Zehner agreed that the two satellites are powerful partners in providing air quality data to European environmental protection agencies.

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