The COVID-19 coronavirus outbreak has caused widespread alarm, travel bans and quarantines in several cities around the world.
But it also had an unexpected impact on the environment in the form of a noticeable reduction in China's nitrogen dioxide emissions.
Data collected using the Tropospheric Monitoring Instrument (TROPOMI) on the ESA Sentinel-5 satellite shows a significant drop in nitrogen dioxide – a gas mainly emitted by cars, trucks, power plants and some industrial plants – between January 1 and February 25.
“This is the first time I have seen such a sharp decline in such a wide area for a particular event,” said Fei Liu, an air quality researcher at NASA's Goddard Space Flight Center.
Although China tends to experience reductions in nitrogen dioxide in late January and early February due to plant closures during the Lunar New Year, the decline continued long after the festival ended this year.
The sensor on NASA's Aura satellite, an ozone monitoring instrument (OMI), also measures the fall of pollutants.
“There is always an overall decline this time of year,” says Barry Lefer, an air quality scientist at NASA. “Our long-term OMI data allows us to see if these amounts are abnormal and why.”
Satellite data isn't the only way to see China's emissions decline.
An early analysis released by Carbon Brief in February found coal use in power plants hit a four-year low and domestic flights were down 70 percent. Along with a drop in steel production and refining, they estimate that this could reduce the country's carbon dioxide emissions by about a quarter in the past few weeks.
However, the fact that industries have reduced carbon dioxide emissions and nitrogen dioxide levels are lower than in China does not mean that the air is cleaner in cities. In mid-February, air pollution levels in Beijing were still 10 times higher than the World Health Organization's recommended level.
“Even without automobile emissions, industrial and coal emissions are enough to plunge Beijing into heavy pollution amid inclement weather,” Ma Jun, director of the Institute of Public and Environmental Affairs, told the South China Morning Post.
“The priority now is to further strengthen industry regulation and coal combustion.”
(Joshua Stevens / Copernicus Sentinel 5P / ESA)
It is important to note that this is not the first time that we have seen a sharp decline in air pollution levels in China. During the 2008 Beijing Olympics, nitrogen dioxide levels dropped over the city, but pollution levels increased again shortly after the end of the Olympics.
Finally, the researchers note that total nitrogen dioxide values this year are lower than last year as China began to apply stricter environmental regulations, as you can see in the satellite images of Wuhan above.
But none of these factors alone are leading to such a significant reduction in nitrogen dioxide, which is likely at least partly caused by the coronavirus outbreak.
“This year, the rate of decline is more significant than in previous years and has lasted longer,” Liu said.
“I'm not surprised because many cities across the country have taken steps to minimize the spread of the virus.”
Sources: Photo: Joshua Stevens / Copernicus Sentinel 5P / ESA
