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A blessing in the skies: How coronavirus is affecting Earth’s atmosphere

In early April, Los Angeles residents were captivated by a photo of their city, free of smog. Usually the smoggiest city in the United States, L.A.’s air has cleared under lockdown, its longest stretch of clean air since 1980.  And it’s not just L.A. — cities around the world have seen declines in pollution levels, as people work from home and practice other social distancing measures during the coronavirus pandemic.

comparison map
Average levels of nitrogen dioxide in March of 2015-19 in the Northeast U.S compared to March 2020 nitrogen dioxide levels.

Dropping NO2 levels

To get a clearer sense of how coronavirus is affecting the atmosphere, a good place to start is by looking at nitrogen dioxide levels. “Burning fossil fuels or biomass and agriculture release large amounts of nitrogen oxides,” Cristina Vrînceanu, a Ph.D. student at the Nottingham Geospatial Institute at the University of Nottingham, told Digital Trends in an email. “NO2 can be measured either in the lower level of the atmosphere, the troposphere, but also high up into the stratosphere, giving us a good picture of the smog events happening on ground and how pollutants affect our sun radiation shield, the ozone layer,” she added.

For her research, Vrînceanu usually uses satellite data to detect natural hydrocarbon sources. But after Italy’s prime minister put the country in a lockdown to help combat the spread of COVID-19 on March 9, she saw an opportunity to start tracking nitrogen dioxide levels over the country and watch if they changed. Using information gathered from the Sentinel-5P satellite, which maps air pollution all over the planet, she started making comparisons between before and after the travel restrictions.

Average levels of nitrogen dioxide in March of 2015-19 in the Northeast U.S.
Average levels of nitrogen dioxide in March of 2015-2019 in the Northeast U.S. NASA Scientific Visualization Studio
March 2020 nitrogen dioxide levels.
March 2020 nitrogen dioxide levels. NASA Scientific Visualization Studio

The Po Valley, in between the Apennines and the Alps in northern Italy, is home to Milan and is known for its high pollution levels. “Due to Sentinel-5P we can now monitor a large piece of the planet and observe daily changes in atmospheric chemistry, gas, and particles transport patterns and capture the events that produce large plumes of aerosols or harmful gas,” Vrînceanu said. “Pollution in northern Italy is one of those cases, as daily nitrogen dioxide output is extremely high in the area and has a strong signature on the Sentinel-5P data.” By looking at the data before and after Italy started to suspend activity in this area, with its high density of commerce, industry, and agriculture. Towards the end of March, Vrînceanu estimated between a 35% to 40% drop in emissions in the area.

Reductions in NO2 levels are showing up all over the globe. NASA found a “significant decrease” over southeast Asia between early January and March 20; China was estimated to have reduced its emissions by 25% in February. India also saw lower levels of NO2 in March. In the northeastern U.S., NASA showed March had the lowest levels of nitrogen dioxide emissions in the last 15 years, when records started. “Similar satellite observations of climate-warming gases such as carbon dioxide are not available as easily or quickly” as NO2 levels, Steve Cole, a spokesperson for NASA, wrote in an email. “It would take scientists many months of data analysis to attempt to tease out a clear CO2 signal over a specific region of the Earth.”

Nitrogen dioxide comparison map of Europe

Some are predicting the pandemic could cause the largest annual fall in carbon dioxide emissions ever seen, as much as 5.5%. Still, it’s too early to tell exactly what will happen. The length and scope of shut-downs will have an impact, and it’s necessary to distinguish what is and isn’t related to COVID-19. The mild winter in some areas, for example, also caused lower fuel use.

Getting a fuller picture of how less commuting and air travel are affecting the planet overall requires a different sort of measurement. On Hawaii’s Mauna Loa volcano sits one of the National Oceanic and Atmospheric Association’s (NOAA) observatories. Its position makes it a good source of well-mixed air without interference from local pollution or vegetation. Reduced emission levels aren’t large enough to register in its samples yet. “We’ve seen no significant drop,” Theo Stein, a NOAA public affairs official, recently told Scientific American.

Even if global emissions do drop 5.5%, that still falls short of the number needed — 7.6% annually — to combat climate change. Otherwise, the United Nations says the planet won’t be able to reach the Paris Agreement’s goal of limiting warming to 1.5 degrees Celsius.

A threat multiplier

paris heatwave
July 25, 2019 as a new heatwave hits the French capital. Getty Images

While drastic changes are needed to meet the Paris Agreement’s goal, a pandemic isn’t the way anyone wanted to reduce greenhouse gas emissions. Many of the same populations that are vulnerable to the effects of climate change are also being harder hit by the coronavirus. Dr. Trish Koman calls climate change a “threat multiplier.” She’s a research investigator at the University of Michigan School of Public Health Environmental Health Sciences department. “If we were to have a significant heatwave at the same time that we’re having a spike in coronavirus patients, it would change our ability to be able to use cooling centers or to be able to appropriately hospitalize and treat patients who are coming in with heat-related illness,” she said.

A preliminary study from the Harvard T.H. Chan School of Public Health suggests that past exposure to pollution is associated with an increased risk of death from coronavirus. Air pollution comes in a variety of different forms, including particulate matter and smog. “These small particles can penetrate deeply into the lungs, through your nasal passages,” said Koman. “ They can get into the brain. They are associated with a wide array of health effects, including heart and lung problems.” Because the virus is causing hyperinflammation and respiratory distress in some COVID-19 patients, prior lung damage from pollutants could be exacerbating the effects.


The past several years have seen increased urgency about dealing with climate change from many governments and individuals. “This has also diverted almost everyone’s attention away from the climate crisis to the immediate hazard,” Michael Gerrard, director of the Sabin Center for Climate Change Law at Columbia Law School, said of the coronavirus. “And we don’t know what longer-term effect that will have.”

China, Shanghai, pollution
Image used with permission by copyright holder

Already, the decreases in China’s emissions levels are starting to rebound as factories reopen. “The only times when the upward trend of global greenhouse gas emissions has gone down has been during global economic downturns that happened during the oil price shocks of the 1970s with the collapse of the Soviet Union in 1989 and with the global economic crisis of 2008 and 2009,” said Gerrard. “In all those instances, energy use and greenhouse gas emissions dipped for a time, but after the crises were over, they resumed their upward trend.” He said it’s unclear how the current pandemic will affect long-term trends.

At least in the U.S., the push from the Trump administration has been toward less energy efficiency, whether it’s on light bulbs or cars. The White House recently rolled back fuel economy standards, which were aimed at reducing fossil fuel emissions. Data show traffic reductions around the country. Cars contribute to nitrogen dioxide emissions, and with so many off the road, it’s led to some of the drops seen in NASA and other agencies’ findings.

In addition to allowing less-efficient vehicles on the road, the Trump administration has also decided not to set stricter air quality standards. Last year, the Environmental Protection Agency’s staff scientists estimated that lowering the annual particulate matter standard could save about 12,200 lives a year.

It’s unclear how long U.S. states will maintain their shelter-in-place directives, or how businesses and schools will adapt once the pandemic has abated — with more telecommuting, for example. “I think that one of the things that we can take away from this very unfortunate situation is that we do have resilience and that we can make these changes when we need to,” said Koman.

“I hope that this crisis leads some to reevaluate their trust in scientists,” said Gerrard, especially when they call for advance preparation, he added. “We’re paying a very high price for disregarding scientists and their warnings.”

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Jenny McGrath
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