China’s infamous pollution problem has seemingly completely disappeared during the coronavirus pandemic, with millions of people staying inside.
The Chinese government has banned travel to and from all affected regions and shut factories while the authorities have ordered residents to stay home, but the total lockdown has given residents unexpected "good-quality air days".
In an animated video using data from the Copernicus Sentinel-5P satellite, a significant drop in nitrogen dioxide emissions levels is seen across China between January and February.
Nitrogen dioxide is a gas mainly emitted by cars, trucks, power plants and some industrial plants.
The colour charts represent the density level of the toxic gas in the air. In northern and eastern China where factories and shipping business resides, the chart indicates yellow and red in the December-January period.
But as soon as the government announced the ban in late January, the map is cleared with no nitrogen dioxide emission recorded on the satellite.
Claus Zehner, ESA’s Copernicus Sentinel-5P mission manager, comments: "We can certainly attribute a part of the nitrogen dioxide emission reduction to the impact of the coronavirus.
"We currently see around a 40% reduction over Chinese cities, but these are just rough estimates, as weather also has an impact on emissions."
Fei Liu, an air quality researcher at NASA's Goddard Space Flight Centre, was quoted by Science Alert as saying: "This is the first time I have seen such a dramatic drop-off over such a wide area for a specific event."
Some said such drop is usually seen during the Lunar New Year as factories are closed and workers go home for celebration, but the reductions have continued long after the end of the festival.
At the end of the video, it shows the emissions levels going up again in March when the Chinese government started lifting travel bans and factories reopened for business.
The Sentinel-5P satellite is dedicated to monitoring air pollution by measuring a multitude of trace gases as well as aerosols – all of which affect the air we breathe.
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