Scientists Discover That Rocket Exhaust Pollution Lingers in the Earth’s Atmosphere for a Disturbing Amount of Time

By simulating the fluid dynamics of rocket exhaust gases, scientists have been able to analyze the atmospheric emissions from rockets

Commercial spaceflights by companies like SpaceX and Virgin Galactic have promoted the use of reusable space technology to cut the cost of space travel. However, few people are aware that rocket propulsion emissions generate significant heating and chemical changes in the atmosphere.

Researchers from the University of Nicosia in Cyprus looked at the heat and mass transfer and quick mixing of combustion byproducts for altitudes up to 67 kilometers into the sky to assess the possible consequences of a rocket launch on atmospheric pollution. On May 17th, 2022, their findings were published in Physics of Fluids by AIP Publishing.

“Improved understanding of rocket emissions requires modeling and simulation of fluid dynamics of rocket exhaust gases into the atmosphere,” stated co-author Dimitris Drikakis.

The scientists studied the exhaust gases and created plumes at various elevations along a typical modern-day rocket route. They did it as a model for a two-stage rocket capable of transporting people and payloads beyond Earth's orbit.

“We show that pollution from rockets should not be underestimated as frequent future rocket launches could have a significant cumulative effect on the Earth’s climate,” said co-author Ioannis Kokkinakis.

The researchers discovered that the generation of thermal nitrogen oxides (NOx), which are components of combustion exhaust, may stay high up to heights where the ambient air pressure is above or even slightly below the nozzles' exit pressure, i.e. below 10 km.

At the same time, as the rocket climbs 1 kilometer in altitude in the mesosphere (the region of the atmosphere between the thermosphere and the stratosphere, located at an altitude of 30-50 miles or 50-80 kilometers), the emitted mass of carbon dioxide is equivalent to that contained in 26 cubic kilometers of atmospheric air at the same altitude.

They discovered that the influence on the atmosphere may be considerable both locally and briefly in the mesosphere. While air currents will progressively move and mix the CO2 from the exhaust throughout the atmosphere, ultimately bringing it back to naturally occurring levels, the time scale over which this will occur is unknown.

Scientists think that a threshold of rocket launches exists at which mesospheric carbon dioxide can collect over time, raising naturally occurring levels and impacting our climate.

Their findings suggest that, in the worst-case scenario, enough NOx could be produced in the time it takes a rocket to reach a height of 10 kilometers to pollute over 2 cubic kilometers of atmospheric air with a NOx concentration that would be hazardous to human health, according to the World Health Organization.

“We hope that commercial flight companies, such as SpaceX, Virgin Galactic, and the New Shepard, and their associated engine manufacturers, will consider these effects in future designs,” Drikakis added.