It cannot be ruled out that frequent rocket launches will eventually affect the atmosphere and our climate.

Cypriot researchers write that in the magazine Physics in Fluids† They are based on models and simulations, in which a widely used propellant: RP-1. “The Saturn V rocket’s first stage used RP-1, as did the Falcon 9 and Falcon Heavy rockets, the Atlas V core stage, Soyuz, and Rocket Lab’s Elektron, just to name a few, so tells researcher Dimitris Drikakis Scientias.nl† “This propellant – RP-1 – uses liquid oxygen as an oxidizer and is simply a highly refined kerosene. Together with the oxidizer, the propellant RP-1 is also referred to as kerolox. A rocket engine that burns kerolox will produce mainly carbon monoxide, carbon dioxide, water vapor and small amounts of hydrogen and hydrogen gas. In addition, soot particles, some sulfur-containing substances and thermal nitrogen oxides can also be formed. The emissions are actually not that different from those of a typical combustion engine as you find in a car. The only difference is that much more emissions are produced in a much shorter time frame.”

Findings

And the simulations — which simulated the release of a kerolox-powered two-stage rocket up to 40 miles (67 km) above the Earth’s surface — show that rocket launches using kerolox do not leave the atmosphere untouched. “We show that missile pollution should not be underestimated,” said researcher Ionnis Kokkinakis. “As the frequent future rocket launches could cumulatively have a significant effect on the Earth’s climate.”

CO2

For example, the rockets appear to release a relatively large amount of CO2 into the atmosphere. “The biggest surprise was the relatively large amounts of carbon monoxide, CO2 and hydrogen that a rocket releases into the atmosphere compared to the amounts we naturally find in the atmosphere at higher altitudes,” Drikakis says. For example, the amount of CO2 that a rocket emits as it climbs 1 kilometer higher in the mesosphere appears to be approximately equal to the amount of CO2 that we find at the same height in about 26 cubic kilometers of air. “That’s because, although the air density in the mesosphere is 4 to 5 orders of magnitude lower than at sea level, the rocket’s emissions remain almost stable during launch.”

Spread

Ultimately, that hefty blast of CO2 is spread through the atmosphere again by air currents, explains Kokkinakis Scientias.nl from. “Our atmosphere is quite turbulent and gradually the high CO2 concentrations left behind by the rocket will spread through the rest of the mesosphere and eventually the entire atmosphere.” And then the CO2 concentration in the mesosphere will be returned to its original (natural) level. At the moment, however, it is unclear how long it will take for this local injection of CO2 to spread over the mesosphere and atmosphere. “What clearly distinguishes rocket launches from other sources of CO2 is that they inject relatively large emissions (such as CO2) directly into the mesosphere and thereby significantly increase local and naturally occurring concentrations. How long that will remain is unknown, but we don’t think the current number of rocket launches is large enough to cause significant problems. However, the injected amount of CO2 may remain in the mesosphere longer than expected. And then more frequent rocket launches could eventually cause naturally occurring concentrations of gases in the atmosphere to change.” And that can – in the case of CO2 for example – influence the Earth’s climate.

NOx

In their study, the researchers not only look at CO2, but also at nitrogen oxides (NOx). “These are created when the air – which is mainly made up of nitrogen and oxygen – is heated up by the hot gases coming out of the rocket,” Drikakis explains. In particular, it was assumed that nitrogen oxides could be formed quite easily in the troposphere – the lowest layer of the atmosphere – because there the air pressure – which decreases as you go higher in the atmosphere – is relatively high and the ease with which nitrogen oxides are formed dictated is caused by that air pressure. “Whether nitrogen oxides can easily be formed usually depends on the pressure at which gases are released from the rocket. As long as that pressure is lower than the local air pressure, the chance that nitrogen oxides will form is much higher, because the plume of gases does not undergo expansion (a process that cools the emitted gases).” But the simulations now show that the nitrogen oxides can still see the light of day even at higher altitudes – where the plume of gases does expand due to a lower air pressure and the gases also cool down. “Shock waves that arise in the expanding plume can even reheat the cooled gases at an altitude of 30 kilometers to a temperature of more than 1000 degrees Celsius, which means that there is also above the tropopause (the boundary between the troposphere and the stratosphere, ed. ) there is a high probability that nitrogen oxides are formed as a result of heat.” There has been much talk about the formation of nitrogen oxides in the past, because they have a harmful effect on health. “There is strong evidence that exposure to NOx can affect the respiratory tract. It can trigger and worsen asthma symptoms and prolonged exposure can even lead to the development of asthma. Non-respiratory-related effects have been less convincingly demonstrated, but NOx has also been linked to heart disease and diabetes, for example.”

And those substances now appear to be able to see the light of day during a launch in a much larger part of the atmosphere. And it also involves the formation of decent amounts; Simulations show that in the period it takes a rocket to reach an altitude of about 10 kilometers, enough NOx is produced to pollute more than 2 cubic kilometers of air with NOx concentrations above the safe levels by the WHO borders and are therefore dangerous to public health.

The prelude to more

The research makes you think. And that’s exactly the point. Because – certainly now that the number of launches is increasing sharply – we can no longer blindly assume that the atmosphere is in no way influenced by rocket engines. At the same time, however, there are also many loose ends, Kokkinakis acknowledges. For example, more research needs to be done on the time it takes for the atmosphere to distribute the gases injected by rockets evenly over itself. Only once we know that, can we look at the potential climate impact and researchers can, for example, calculate the number of rocket launches we will get into trouble – in a given time frame.

“Our goal was to alert the engineering and scientific community, aerospace companies and the public to the potential risks and encourage further research into this issue,” Drikakis said. As far as the latter is concerned, the Cypriot researchers already set a good example; for example, they intend to conduct research in the near future into the impact of rocket engine emissions on atmospheric ozone.