As private space companies race to make spaceflight routine, Earth's upper atmosphere has become an inadvertent testing ground. Every launch demonstrates human wisdom, but there is also a formula hidden behind it that no one pays attention to: Rocket exhaust gas and propellant residue react with ozone, weakening this barrier that protects life on earth. This problem is now being gradually quantified by scientists, and its impact is rising as rapidly as the rocket itself.
In the 1980s, the world was highly alerted to the atmospheric crisis caused by synthetic chemicals chlorofluorocarbons (CFCs). CFCs are widely used in refrigerants and aerosol cans, causing holes in the ozone layer and allowing harmful ultraviolet rays to penetrate in large amounts. The global response was swift and unified: the 1987 Montreal Protocol banned ozone-depleting substances and set a strict phase-out timetable. CFC emissions fell by 99% as a result, and by 2025, satellite data showed that since recovery the Antarctic ozone hole had shrunk to one of its smallest sizes in history.
But as a chapter of atmospheric destruction comes to an end, new hidden dangers quietly emerge. The surge in commercial rocket launches - including the deployment of satellite networks and space tourism - is leading to what scientists are calling a "new era of rocketry." The number of annual launches has doubled since 2019, with each launch leaving a unique chemical trail high in the stratosphere.
Each mission through the stratosphere releases exhaust gases, chlorine-containing substances in solid propellants, metal particles from engines and black carbon soot from fuel combustion. These residues not only cause a greenhouse effect in the upper atmosphere, but also trigger a series of ozone-destroying chemical reactions, affecting exactly where the ozone layer is most vulnerable.
Sandro Vattioni, a researcher at the Federal Institute of Technology in Zurich (ETH Zurich), and his team conducted a modeling study in 2024 and pointed out: "The surge in the number of global rocket launches may slow down the recovery process of the key ozone layer." Vattioni's team said that the current impact of rockets is still limited, but the ozone layer is still about 2% thinner than before the CFC crisis, indicating that although recovery is in progress, it has not yet been completed.
A team from the University of Canterbury (Laura Revell) in New Zealand further analyzed several future growth paths for the global launch industry based on Vattioni's model. Under medium assumptions (about 884 launches per year), global ozone will decrease by about 0.17% by 2030. Under the high-growth scenario, the annual number of launches is close to 2040, and global ozone loss increases to 0.29%, reaching nearly 4% over Antarctica.
This percentage may seem small, but the chemical process of ozone is not linear. Small changes can be enough to slow recovery and erode decades of global collaboration. Both studies agree: Without a clean transition in propulsion technology, rapid expansion of the launch industry could offset much of the progress made under the Montreal Protocol.
The key to scientific warning lies in the chemical reactions that occur in the rocket exhaust.
The main culprits in ozone depletion from rockets are chlorine and soot. Chlorine catalytically destroys ozone molecules, while soot heats the mid-atmosphere, exacerbating similar reactions. Most propellants leave a soot mark, but chlorine comes primarily from solid rocket motors. Rockets using low-temperature liquid propellants such as oxygen and hydrogen have almost no impact on ozone, but due to complex technology, they currently only account for about 6% of the total number of launches.
And the impact doesn't stop at takeoff. Vattioni's model stops at the launch stage, and the satellite's reentry into the atmosphere may hide greater risks. Low-orbit satellites will release nitrogen oxides and metal dust during crashes. Nitrogen oxides can directly deplete ozone, and metals can stimulate the formation of polar stratospheric clouds or provide surface accelerators for ozone-depleting reactions.
Such re-entry effects have not yet been systematically recognized and are mostly undocumented by existing models. As the number of satellites continues to proliferate, such "hot returns" will become increasingly frequent, and the overall ozone impact may be much higher than currently estimated.
The study's conclusions paint a future that depends on coordinated science and policy. To avoid further ozone losses, we must continue to track rocket emissions, phase out high-chlorine and high-smoke fuels, promote clean technology upgrades, and embed processes for launch supervision. As the ozone crisis of the 1980s showed, atmospheric changes always occur quietly, but disasters often occur unprepared.