Boeing’s approach in mitigating Contrails.

What is a Contrail –

A Contrail is a type of cloud that forms in the wake of an aircraft at high cruise altitudes under specific temperature and humidity conditions when water vapour condenses onto emitted aerosols and then freezes to form ice particles. Some contrails dissipate quickly and have a negligible climate impact, but those that persist may contribute to either a warming or cooling climate impact, depending on ambient conditions and the timing of formation.

An Aircraft Engine emits water vapour and soot; the vapour thus condenses on emitted aerosols under specific temperature and humidity conditions. The Droplets then freezes into ice particles under specific temperature & humidity conditions. While it is difficult to compare contrails impact to CO2 impact because, while CO₂ is evenly mixed in the atmosphere with a centuries-long lifespan, contrails form in more limited locations and are shorter lived.

Contrail’s contribution to warming –

Studies have estimated that, globally, the warming effect from contrails is greater than the cooling effect. The percentage of flight distance is estimated to contribute to the majority of contrail warming impacts. Contrail contributions to warming are difficult to quantify due to these factors:

• Limited humidity observations available to improve contrail persistence and impact predictions.

• Challenges of representing ice supersaturation, contrails and cirrus clouds in atmospheric models.

• Ice-forming properties of particulate matter in engine emissions.

• Impact of ambient conditions on warming or cooling effects.

Boeings approach to Contrail’s –

Boeing has brought together a team of engineers and scientists from across airplane technology, emissions, atmospheric science, operational efficiency and digital services to drive progress on the path forward; since achieving contrails impact mitigation requires involvement from standard’s bodies, global meteorological services, air traffic management, engine companies, fuel producers and more.

The aviation major has entered into a multiyear partnership with NASA and others to study how sustainable aviation fuel (SAF) affects contrails and non-CO2 emissions while in flight. From 2021-2023, the team conducted ground and flight tests to assess how SAF affects the characteristics of contrails. The researchers aim to understand how advanced fuels, engine combustor designs and other technologies may reduce contrail formation and persistence. It is also working to enable operational mitigation through efforts to increase the fidelity of upper tropospheric humidity data to create more accurate contrail forecasts, develop digital services that incorporate uncertain contrail information into decision making, and conduct research to better understand the airspace effects of scaled operational avoidance.

Critical Research & Technology –

Boeing has joined with partners across the industry to author a statement setting priorities for research and technology development needed to improve the science of aviation’s non-CO2 effects, including contrails, and enable the industry’s path forward.

• Improve understanding of contrail formation, persistence, and climate impact.

• Improve understanding of emissions properties.

• Build research on aerosol cloud interactions.

• Improve understanding of the radiative impact and modeling uncertainty of NOX emissions.

• Improve understanding of the interdependencies and trade-offs of aviation emissions (NOX,    soot, contrails, CO2 and noise).

• Establish and improve common models for quantifying the effect of aviation on climate.

• Further investigate research on airspace network impacts of mitigation.

Possible pathways to minimise the climate impacts of contrails include:

• Advancing engine combustion technology to reduce particulate matter

• Changing fuel composition to lower fuel aromatic and sulfur content

• Improving upper tropospheric humidity forecasts and leveraging satellite observations to         enable operational contrail mitigation.

Team Maverick