Atmospheric scientist Christopher Maloney and his colleagues modeled how black carbon spewed from rockets around the world is likely to gradually heat parts of the middle atmosphere and destroy the ozone layer. Their findings were published June 1 in the Journal of Geophysical Research: Atmospheres.
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Maloney and his colleagues' models start with typical launch trajectories, in which rockets shoot a spray of tiny particles, called aerosols, from their engine nozzles. The most dangerous component of the exhaust, however, is black carbon, or soot. Rockets release tons of these tiny particles into the stratosphere, especially between 15 and 40 kilometers above the ground, above the altitude at which airplanes. Modern engines also emit black carbon, but in much smaller amounts. satellites also emit aerosols as they burn up in the stratosphere. Since these particles remain in the stratosphere for about four years, they can accumulate, especially in areas with heavy space traffic.
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Maloney and his team used a high-resolution climate model to predict the effects of this pollution on the atmosphere, studying how aerosols of different sizes could warm or cool regions of space at different latitudes, longitudes and altitudes. They found that within two decades, temperatures in parts of the stratosphere could rise by as much as 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, and that the ozone layer could thin slightly in the Northern Hemisphere. Overall, they conclude that more rockets mean more warming and increased ozone loss, which could be a problem, especially because people, wildlife and crops need the ozone layer to protect them from ultraviolet radiation.
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According to their calculations, each year rocket launches collectively release about 1 gigagram, or 1,000 metric tons, of black carbon into the stratosphere. Within two decades, that could easily increase to 10 gigagrams or more, thanks to the increasing number of rocket launches. The researchers consider multiple black carbon emission scenarios, including levels as high as 30 and 100 gigagrams, which, while extreme, could occur within a few decades if rocket engine technologies and trends don’t change much. They focus their analysis on widely used kerosene-burning rocket engines, such as the first-stage boosters of SpaceX’s Falcon 9, Rocket Lab’s Electron, and Russian Soyuz rockets.
So how can space agencies and companies better protect the atmosphere? Maloney and his team studied mostly rockets that burn kerosene, but types with other hydrocarbon propellants likely emit similar amounts of black carbon. Certain fuel and engine types, including those that burn hydrogen, could be cleaner. And international regulations, such as the Montreal Protocol, which phased out ozone-depleting CFCs from a wide range of products and activities, could also help, they argue.
