Data from NASA and the European Space Agency (ESA) pollution monitoring satellites show a sustained decrease in nitrogen dioxide (NO2) over China since the beginning of this year. According to NASA, this is “at least partly” related to the economic slowdown that has ensued from the outbreak of coronavirus.
COVID-19, the disease caused by the SARS-CoV-2 virus, has at the time of writing infected almost 90,000 people and claimed the lives of just over 3,000. Most of the victims have been in the Hubei province in China, where the virus originated. Following the outbreak, people have been under movement restrictions across China, which at one point reportedly affected 500 million people. From transportation halting in Wuhan at the end of January, to local businesses shutting, quarantine measures are being carried out across the country to reduce the spread of the virus.
Like these restrictions, NASA scientists noticed the reduction of NO2, a harmful gas emitted by motor vehicles, power plants, and industrial facilities, first became apparent near Wuhan then spread across the country.
“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 in a statement.
From the information collected by the Tropospheric Monitoring Instrument on ESA’s Sentinel-5 satellite, and a related sensor, the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite, NO2 pollution levels across China have been mapped in several periods: from January 1-20, 2020 (before quarantine), Jan 28-Feb 9, 2020 (Chinese New Year celebrations), and February 10-25, 2020 (during the quarantine).
Past observations indicate a usual decrease around Lunar New Year celebrations, when many businesses and factories close in China and much of Asia. However, unlike in 2019 the NO2 levels did not rise again afterwards.
“There is always this general slowdown around this time of the year,” Barry Lefer, an air quality scientist at NASA, explained. “Our long-term OMI data allows us to see if these amounts are abnormal and why.”
Using OMI’s data, researchers compared NO2 levels in 2020 with the average amounts detected at the same time of year from 2005-2019. They found that in eastern and central China the levels were between 10 to 30 percent lower than what is normally observed for this time period.
This significant decrease may have other contributing factors beyond the coronavirus quarantine and Chinese New Year celebrations. Lefer noted environmental regulations that China has enforced over the past few years. Previous dramatic decreases in NO2 levels have been observed in several countries, for example during the 2008 economic recession. However, this recent reduction has been much more rapid, leading researchers to believe this event is more than a holiday effect or weather-related variation.
“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.”
This has not been the only time that environmental changes have coincided with global outbreaks of disease. A study from 2017, revealed that the 14th century Black Death outbreak occurred at the same time as the air was lead-free; the first and only time this has happened over the last two millennia. The demographic and economic collapse from the pandemic interrupted metal production, which led the researchers to believe this was at least part of the explanation for the environmental differences.