Silver patches and strands represent nitrogen dioxide emissions, a gas produced by combustion that contributes to acid rain, haze, and lung problems. While there are natural sources of nitrogen dioxide, people are major emitters, according to the Environmental Protection Agency.
Fuel-burning cars, trucks, power plants, factories, and even lawn mowers and construction equipment can pump nitrogen dioxide into the atmosphere. Forest fires and agricultural burning can, too. “You’re looking at a map showing where things are being burned,” says Laura Mazzaro, an atmospheric scientist and environmental engineer at Descartes.
The data comes from the Sentinel 5P satellite — a satellite launched in October 2017 that monitors the atmosphere. It’s part of a family of satellites launched by the European Space Agency that are designed to observe our planet. Other satellites in the series look at things like vegetation, temperature, and even watch for cracks in Antarctic ice.
This particular map is one version of a series of images that Descartes Labs released earlier in February, first reported by Axios. To make them, researchers at Descartes created a composite from individual images that the Sentinel-5P satellite captured during August and September 2018, according to Tim Wallace, graphic design lead at Descartes. Cloudy days and low quality images were filtered out to generate a map of the average amount of nitrogen dioxide in the lowest part of Earth’s atmosphere “on any given day during those two months,” Wallace says.
Nitrogen dioxide doesn’t survive long enough in the atmosphere to travel far from where it’s produced. So you’d expect to see nitrogen dioxide emissions concentrated over cities, where more people are driving cars. But there are also some unexpected sources, Wallace says. “There are ship tracks, and industrial towns in the middle of nowhere,” he explains.
Combined with the nitrogen dioxide shining over the cities, those traces along otherwise dark portions of the map offer a clear picture of the ways we humans contaminate the air we breathe, almost everywhere we go.