We are a month in to measures to mitigate the spread of Covid-19 throughout the United States, and the lack of human activity in the nation's biggest cities is leaving a mark so large you can see it from space.
On Thursday, NASA released new satellite data revealing a dramatic reduction in the levels of nitrogen dioxide over metropolitan areas of the Northeast US. These are the lowest monthly atmospheric nitrogen dioxide levels recorded over the region since 2005, when NASA's Ozone Monitoring Instrument (OMI) began operating.
Overall, the nitrogen dioxide levels in March 2020 are about 30 percent lower than they were compared to the average levels recorded from March 2015 through March 2019.
These charts showing average levels from the past five years show just how stark the difference really is:
The above visualization covers across the region of the I-95 corridor, revealing air pollution levels above cities such as Washington, D.C., New York, Boston, and Philadelphia.
Nitrogen dioxide is one of the most abundant greenhouse gas pollutants, generated by burning fossil fuels for electricity or transportation. As measure to contain the novel coronavirus place restrictions on people's mobility and businesses, the effects resonate in the levels of air pollutants.
The link between Covid-19 and climate change
The US is not alone in seeing such dramatic changes in air pollution levels. Similar effects have been observed across the world. Both NASA and European Space Agency satellites have spotted a significant decrease in air pollution levels over countries such as China, Italy, and France.
Satellite imagery provide a good proxy for nitrogen dioxide levels on the ground, but natural weather variations like cloud cover or changes in temperatures could affect the accuracy of the space-based observations. Further analysis will be needed to work out just how far air pollution levels have truly dropped across the world as a result of social distancing, isolation, and other stringent public-health measures designed to curb Covid-19.
While preliminary, the NASA visualization does provide an initial glimpse at the silver linings of reduced human activity, and what it may mean for the quality of the air that we breathe. Air pollution has devastating effects on human health, killing around 7 million people per year, according to the World Health Organization.
NASA's OMI is a part of the Aura mission, which launched in July 2014. Aura measures trace gases in the atmosphere by detecting their unique spectral signatures. The satellite data helps link changes in air quality to the ongoing effects of climate change, ultimately informing the policies that may help guide the world through the climate crisis.