The ozone layer is doing better, but it is still under threat

The ozone layer is doing better, according to the US National Oceanographic and Atmospheric Administration, but could be threatened by space exploration in the coming decades. The average temperature of the stratosphere could increase by 0.5 to 2 °C.

Analysis of air samples taken from around the world earlier this year shows that concentrations of ozone-depleting chlorofluorocarbons (CFCs) in the stratosphere have returned to 1980 levels. These slow constants of progress were achieved thanks to compliance with regulations adopted under the Montreal Protocol in 1987.

The conclusions are based on two indices, one for mid-latitudes, where most of the world’s population lives, and one for Antarctica, where the most significant ozone holes are observed in early spring.

Development of the concentrations of chlorine and bromine products in the stratosphere from 1970 to 2021 and forecasts for the 21st century. In blue, concentrations at mid-latitudes. In green: concentrations over Antarctica. [NASA/Laboratoire de surveillance mondiale de la NOAA]

Progress in the mid-latitudes has been relatively rapid, but the same has not been true in the areas over Antarctica, where CFC concentrations have decreased by only 26% from peak levels observed in the 1990s. The phenomenon can be explained for many reasons, but primarily because the air in the Antarctic stratosphere renews very slowly compared to mid-latitudes.

Due to this relative slowness, the researchers of the NOAAestimate that the Antarctic ozone layer will not return to 1980 levels until 2070.

Increased space travel threatens the ozone layer

If the ozone layer tends to recover, the increase in the number of space flights could change things in the coming decades. The soot emitted by rocket reactors comes into question:

Soot, also known as soot, results from the incomplete combustion of fossil fuels. It exerts its effects on the environment near the earth’s surface, but also in the upper layers of the atmosphere when injected into the stratosphere.

Soot tends to absorb incident sunlight in the stratosphere and transmit it as heat, causing temperatures to rise. Since the beginning of the 21st century, the phenomenon has taken on a special proportion. According to NASA estimates, around 1,000 tons of soot are thrown into the atmosphere every year when rockets are launched.

Launch of a Falcon 9 rocket from SpaceX [SpaceX/Wikipedia]Launch of a Falcon 9 rocket from SpaceX [SpaceX/Wikipedia]

However according to a to learn, released by NOAA’s Chemical Sciences Laboratory in early summer, rocket launches are expected to increase tenfold over the next 20 years for space tourism, lunar missions and solar system exploration. The annual amounts of soot introduced into the stratosphere could thus increase global stratospheric temperatures by 0.5 to 2 °C.

Such a rise in temperature in the stratosphere could cause significant changes in the general circulation of currents. Researchers fromETH Zurich, for example, has found that the depletion of ozone over the Arctic in the spring leads to abnormal weather patterns over the northern hemisphere, where many places are hotter than average and dry — or too humid.

In their modeling, the NOAA researchers also found that a 10-fold increase in soot levels in the stratosphere would cause the ozone layer to become thinner over the northern hemisphere for most of the year.

“Ultimately, the projected increase in rocket launches could expose people in the northern hemisphere to increased levels of harmful UV radiation,” said Christopher Maloney, lead author of the study.

The choice of rocket type is crucial for the future of the ozone layer

Blue Origin’s New Shepard rockets, which send tourists into space at an altitude of about 100 km, don’t need much energy. They are equipped with BE-3 type reactors that use a combination of liquid hydrogen and liquid oxygen that produces only water vapour: their environmental impact is relatively small.

The situation is different when launching observation satellites or sending probes to Mars or the Moon, which require much more powerful launch vehicles. For example, kerosene burned by the Merlin engines of SpaceX’s Falcon 9 rockets produces copious amounts of soot. The same applies to the so-called hybrid engines of Virgin Galactic’s SpaceshipTwo space plane, which combine a solid fuel with a liquid or gaseous oxidizer.

Launch of a Blue Origin New Shepard rocket on June 19, 2016 [Blue Origin/Wikipedia]Launch of a Blue Origin New Shepard rocket on June 19, 2016 [Blue Origin/Wikipedia]

Efforts have been made by manufacturers: for example, the Raptor engines that SpaceX uses to test their booster burn a combination of liquid oxygen and liquid methane. Blue Origin’s BE-4 engines, destined for the New Glenn rocket, will use a similar mixture of liquid oxygen and liquefied natural gas (LNG). These mixtures are based on fossil fuels but burn much cleaner than kerosene or solid fuels. Above all, they should emit less soot.

Positive of course. But the problems of soot emissions are far from solved…

Philippe Jeanneret with support from NOAA and Meteomedia-Canada

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