The US space agency noted that 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 in a news release.
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, but they normally rebound once the celebrations are over.
“This year, the reduction rate is more significant than in past years and it has lasted longer,” Liu said.