"This is the first time I have seen such a dramatic drop-off over such a wide area for a specific event," said NASA air quality researcher Fei Liu. She made that statement after NASA's Earth Observatory released maps showing a dramatic drop in air pollution in the Wuhan region. Industrial output in the region would have already been down significantly due to the Lunar New Year. However, a government quarantine designed to stop the spread of the coronavirus disease COVID-19 made pollution drop much more significantly and for a longer period.

Maps of the Wuhan region from January 1st to February 25th, 2019 show a noticeable drop in air pollution during the Lunar New Year. However, pollution levels quickly rebounded, as seen in the dark red images from the same time last year.

This year has been another story, however. The virus story started to explode early in the New Year, after Chinese authorities had confirmed that the illness was caused by a new coronavirus similar to those that caused the SARS and MERS outbreaks. By January 23rd, the government had shut down all transportation into and out of Wuhan, while closing local businesses and factories in an effort to slow the spread of the virus.

As a result, NASA's NO2 maps of the region during the same period in 2020 show very light levels of pollution (as blue, rather than yellow and red) on the maps. Another key indicator of pollution, ozone, shows a similar result, according to NASA. Liu said that the agency has mapped pollution drops around Beijing during the 2008 Olympics, and in other nations around the 2007-2009 economic recession, but never to that level.

One of the great values of an airborne observatory is that scientists can assess pollution events and compare them to past periods. "There is always this general slowdown around this time of the year," said NASA air quality scientist Barry Lefer, an air quality scientist at NASA. "Our long-term OMI data allows us to see if these amounts are abnormal and why."

This time, the decrease is more than a holiday-related dropoff compared to past events going back to 2005. Overall, NO2 values during the COVID-19 outbreak were from 10 to 30 percent lower than what is normally seen at this time of year.

While that provides some breathing relief for residents, the coronavirus has devastated the region, causing nearly 3,000 deaths so far in China. "I am not surprised [about the pollution drop] because many cities nationwide have taken measures to minimize spread of the virus," said Liu.

Source: NASA Earth Observatory

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