Chinese authorities have taken drastic steps to contain the virus, curbing the movement of people, temporarily closing factories across the country and quarantining central Hubei province, a key industrial region where the epidemic first appeared. NO2 is a byproduct of fossil fuel combustion in vehicles and power plants and can cause respiratory problems, such as asthma.
"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's Goddard Space Flight Center, said. The 2008 global financial crisis saw a decrease in NO2 over several countries but it was a gradual fall, she said. This year's fall came during the Lunar New Year, when factories and businesses close, but researchers believe the decline is far greater than could be attributed to the holiday period.
NO2 concentrations over eastern and central China were 10-30 percent lower than what is normally observed over the time period. And there has not been a rebound in levels after the holiday. "This year, the reduction rate is more significant than in past years and it has lasted longer," Liu said.
"I am not surprised because many cities nationwide have taken measures to minimize spread of the virus." A separate study in February found China's carbon emissions had dropped by least 100 million metric tonnes in the previous fortnight - nearly six percent of global emissions during the same period last year.