Air pollution over China has plummeted in the wake of the coronavirus outbreak that forced the shutdown of industry and transport, NASA says.
NASA and the European Space Agency's pollution monitoring satellites have detected a significant decline in the amount of nitrogen dioxide (NO2) — a noxious gas emitted by cars, power plants and factories.
"There is evidence that the change is at least partly related to the economic slowdown following the outbreak of coronavirus," NASA said in a statement.
According to NASA, the reduction in NO2 was first apparent near Wuhan, the epicentre of the virus, where millions of people were quarantined.
"This is the first time I have seen such a dramatic drop-off over such a wide area for a specific event," research scientist Dr Fei Liu said.
The drop in pollution also coincided with the Lunar New Year, when most businesses in China close.
"There is always this general slowdown around this time of the year," NASA air quality scientist Barry Lefer said.
But NASA's Earth Observatory said that: "While the Lunar New Year may have played a role in the recent drop-off, researchers believe the decrease is more than a holiday effect or weather-related variation."
It noted that pollution levels had not risen as expected after the New Year holiday.
NASA has been collecting global data on NO2 and various air pollutants for more than 15 years.
This is not the first time decreases have been recorded in China.
"Scientists also observed a significant reduction around Beijing during the 2008 Olympics, but the effect was mostly localised around that city, and pollution levels rose again once the Olympics ended," NASA said.
