Satellite images have shown a dramatic decline in pollution levels over China, which is "at least partly" due to an economic slowdown following the outbreak of the new coronavirus, NASA says.
Images by NASA and the European Space Agency show how levels of nitrogen dioxide – a noxious gas emitted by motor vehicles and industrial facilities – plummeted in February compared to January, before authorities imposed lockdown measures.
NASA scientists said the reduction in nitrogen dioxide levels was first apparent near the city of Wuhan, where the outbreak of COVID-19 began. It then spread across the country.
The US space agency noted the decline coincided with transport and business restrictions, and as millions of people went into quarantine.
"This is the first time I have seen such a dramatic drop-off over such a wide area for a specific event," Fei Liu, an air quality researcher at NASA, said.
A composite image of comparative levels of nitrogen dioxide over Wuhan. Photo: AAP
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Scientists had previously observed gradual declines in nitrogen dioxide levels during the 2008 global financial crisis, and more localised reductions during the Beijing Olympics the same year.
China's Lunar New Year celebrations in February have been linked to such decreases in pollution levels in the past. Levels normally rebound once the celebrations are over.
"This year, the reduction rate is more significant than in past years and it has lasted longer," Dr Liu said.
"I am not surprised because many cities nationwide have taken measures to minimise spread of the virus."
Tweet from @NASA
China has recorded 79,826 cases of the novel coronavirus since the outbreak began in December and 2990 people have died from COVID-19 worldwide, most of them in China.
The disease is spreading rapidly around the globe, with more than 60 countries now confirming infections.