More and more research confirms the adverse impact that contrails have on the climate, but what about those particles emitted by aircraft engines that don’t always form contrails, yet remain in the air? Are they affecting the environment?
According to the Environmental Protection Agency (EPA), aircraft engines emit carbon dioxide (CO2), nitrogen oxides (NOx), soot, sulfur gases, and a host of other particles. These all interact with the atmosphere in their own ways, but let’s start with the soot that comes spewing out of the aircraft exhaust.
In 2019, researchers at Michigan Technical University used their cloud chamber to attempt to recreate observations that compacted soot particles in the air form cloud droplets. Janarjan Bhandari and Claudio Mazzoleni used a cloud chamber to simulate how soot particles in the air compact to form cloud droplets when they are “cloud processed”. These droplets, especially the larger ones, clump together and create cirrus clouds. Bhandari and Mazzoleni discovered that the longer the soot particles remain in the air, the more likely they will become compacted. 1 In these unnatural cloud structures, the dark hues of the soot particles absorb the sunlight more than other aerosols and have a greater warming influence.
Although soot is released into the air in various ways, aviation is one of the leading contributors of putting it directly into the upper atmosphere. According to a 2023 study published by the American Chemical Society, “[a]bout a million tons of [soot] nanoparticles are released every year by aviation through incomplete combustion of jet fuel.” 2 As these particles accumulate, they form cloud systems that affect evaporation and precipitation. The clouds that are formed disrupt weather cycles and contribute to warmer, more humid temperatures.
As mentioned in the EPA article, jet engines also emit sulfur and NOx. Although aviation is not the primary emitter, these particles have a significant impact on the environment, particularly when flights take off and land. The scientific journal, Atmospheric Chemistry and Physics, published a study in 2016, in which researchers tested the effects of sulfur, NOx, and other particles present in aviation fuel and found that they increase the levels of cloud condensation nuclei (cloud seeds), which in turn impact Earth’s sensitivity to radiative forcing.
These adverse warming and weather-disrupting cloud formations stemming from the particles in jet fuel and contrails are bad news for the environment. But it’s not all bad; in that same study in Atmospheric Chemistry and Physics, they tested Ultra Low Sulfur Jet fuel (ULSJ) and discovered that “[a] scenario with desulfurized fuel and zero NOx emissions reduces the global aviation-induced aerosol burden by 88.3%.” 3
Rerouting planes is one effective and exciting way to eliminate contrails and their climate impact, but more steps need to be taken to limit the use of jet fuels with those pesky particles as well. That’s where ULSJs, Sustainable Aviation Fuels (SAFs), and hydrogen-powered engines will play a major role.
We’ll keep following the research and provide as much information on the progress towards ending the lines as we can.
[1] Bhandari, J., China, S., Chandrakar, K.K. et al. Extensive Soot Compaction by Cloud Processing from Laboratory and Field Observations. Sci Rep 9, 11824 (2019). https://doi.org/10.1038/s41598-019-48143-y
[2] Georgios A. Kelesidis, Amogh Nagarkar, Una Trivanovic, and Sotiris E. Pratsinis Toward Elimination of Soot Emissions from Jet Fuel Combustion 2023 57 (28), 10276-10283 DOI: 10.1021/acs.est.3c01048
[3] Kapadia, Z. Z., Spracklen, D. V., Arnold, S. R., Borman, D. J., Mann, G. W., Pringle, K. J., Monks, S. A., Reddington, C. L., Benduhn, F., Rap, A., Scott, C. E., Butt, E. W., and Yoshioka, M.: Impacts of aviation fuel sulfur content on climate and human health, Atmos. Chem. Phys., 16, 10521–10541, https://doi.org/10.5194/acp-16-10521-2016, 2016