With China reeling under the coronavirus outbreak (COVID-19), satellite images released by the National Aeronautics and Space Administration (NASA) and the European Space Agency’s (ESA) revealed that airborne nitrogen dioxide (NO2) levels have significantly decreased over the country, reflecting the slowdown in economic activity and curbs on movement.
On Saturday, NASA released the images and said that there is evidence that the change is “at least partly related to the economic slowdown following the outbreak of coronavirus”.
The data was collected by the Tropospheric Monitoring Instrument (TROPOMI) on ESA’s Sentinel-5 satellite. The Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite has also been making similar measurements.
A map released by the space agency shows concentrations of NO2 which is emitted by motor vehicles, power plants, and industrial facilities. The data shows the levels of NO2 over China from January 1-20, 2020, before the country started quarantining people, and February 10-25, during the quarantine period.
“This is the first time I have seen such a dramatic drop-off over such a wide area for a specific event,” said Fei Liu, an air quality researcher at NASA’s Goddard Space Flight Center.
“This year, the reduction rate is more significant than in past years and it has lasted longer. I am not surprised because many cities nationwide have taken measures to minimize spread of the virus,” she added.
She added that there had been this level of drop in NO2 over several countries during the economic recession that began in 2008, but it was gradual.
“There is always this general slowdown around this time of the year,” said Barry Lefer, an air quality scientist at NASA.
“Our long-term OMI data allows us to see if these amounts are abnormal and why,” he added.
While researchers believe that the Lunar New Year may have played a role in the entire drop off, they also believe that the decrease is more than a holiday effect or a weather-related phenomenon. Authorities in China had also shut down transportation system connecting to Wuhan, the epicentre of the outbreak, and local business to restrict the infection from spreading further.
In its press release, NASA wrote, “In a preliminary analysis, NASA researchers compared NO2 values detected by OMI in 2020 with the average amounts detected at this time of year from 2005-2019. In 2020, NO2 values in eastern and central China were significantly lower (from 10 to 30 percent lower) than what is normally observed for this time period”.
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