NASA satellite images have shown a dramatic fall in pollution over China that is “partly related” to the economic slowdown due to the Covid-19 outbreak, said the US space agency.

The reduction in nitrogen dioxide (NO2) pollution was first noticed near Wuhan, the epicentre of the outbreak, and eventually spread across the country, according to Nasa scientists who examined data collected by their and European Space Agency satellites.

Maps comparing NO2 concentrations showed a marked decline between January 1 and 20, before a sweeping quarantine was imposed on Wuhan and other cities, and February 10 to 25.

“There is evidence that the change is at least partly related to the economic slowdown following the outbreak of the coronavirus,” said Nasa’s Earth Observatory in a statement.

Chinese authorities have taken drastic steps to contain the virus, including 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 by-product 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,” said Fei Liu, an air quality researcher at Nasa’s Goddard Space Flight Centre.

The 2008 global financial crisis saw a decrease in NO2 over several countries, but it was a gradual fall, she said.

This year’s decline came during the Lunar New Year, when factories and businesses closed, but researchers believe that the drop is far greater than could be attributed to the holiday period alone.

NO2 concentrations over eastern and central China were 10% to 30% lower than what is normally observed over the 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,” said Liu.

“I am not surprised because many cities nationwide have taken measures to minimise the spread of the virus.”

A separate study last month found that China’s carbon emissions dropped by least 100 million metric tonnes in the previous fortnight – nearly 6% of global emissions in the same period last year.

According to the Centre for Research on Energy and Clean Air in Finland, the coronavirus’ rapid spread led to a drop in demand for coal and oil, resulting in the emissions slump. – AFP, March 2, 2020.