Airbus, alongside nine partners from four European countries, has launched PACIFIC to investigate aviation’s non-CO2 emissions and their effects on local air quality and climate, zeroing in on contrails.
These wispy trails, formed when water vapor from aircraft engines condenses around soot and other particles in cold, humid air, don’t just vanish.
Persistent contrails can spread into cirrus-like clouds, trapping heat in the atmosphere and amplifying global warming—potentially more than CO2 alone.
Studies suggest Sustainable Aviation Fuels (SAF) could reduce soot and ice crystal formation in contrails, but fuel composition and engine processing details remain unclear, necessitating deeper research.
The Contrail Problem
Contrail persistence refers to the ability of contrails to remain in the sky for extended periods rather than quickly dissipating. This happens under specific atmospheric conditions, primarily when the air at cruising altitude (typically 30,000–40,000 feet) is cold and humid.
When an aircraft engine burns fuel, it releases hot exhaust containing water vapor, carbon dioxide, and tiny particles like soot. In the frigid upper atmosphere (often below -40°C), the water vapor rapidly condenses around these particles, forming ice crystals that make up the visible contrail.
If the surrounding air is dry, these ice crystals quickly evaporate, and the contrail fades within seconds or minutes—a short-lived contrail.
Water Vapor Exacerbates the Problem
However, persistence kicks in when the air is already near or above its saturation point for water vapor. In these supersaturated conditions, the added moisture from the exhaust doesn’t evaporate.
Instead, the ice crystals grow by absorbing ambient water vapor. This can sustain the contrail for hours, allowing it to spread out and sometimes merge into thin, cirrus-like clouds covering large areas.
The process depends on factors like temperature, humidity, wind shear, and the amount of particulate matter in the exhaust, which acts as “seeds” for crystal formation.
Persistent contrails matter because they affect the climate. While short-lived contrails have minimal impact, persistent ones trap outgoing heat (infrared radiation) from Earth, contributing to a warming effect known as radiative forcing.
About PACIFIC
PACIFIC – Particle emissions, Air Quality, and Climate Impact related to Fuel Composition and Engine Cycle – will test an extensive range of fuels under controlled conditions.
Experiments will maintain uniform combustion settings and hardware, scaling from lab trials at the German Aerospace Center (DLR) to full engine tests in Toulouse.
The project aims to decode soot formation during combustion, using upgraded tools to predict its presence in exhaust.
It will also measure fine particle output across engine power levels, refining impact estimates from ground to flight scenarios.
A major focus is how particles spark ice crystals in contrails. These crystals can linger for hours, reflecting sunlight but also trapping heat, which complicates their climate impact. Advanced measurement methods will track this process.
Additionally, PACIFIC will explore how fuel blends and engine settings alter contrail properties and their warming effects.
By synthesizing these findings, the project will support a detailed cost-benefit analysis of fuel options, informing future regulations and fuel standards to curb aviation’s environmental toll while bolstering Europe’s sustainable aviation leadership.
Conclusion
Airbus CTO Sabine Klauke emphasizes the urgency. “Cutting non-CO2 emissions is key to sustainable flight,” she says. “Through collaborative, science-driven efforts, we aim to minimize these impacts while preserving efficiency.”
“PACIFIC will analyze SAF emissions with a novel ground-testing approach that replicates conditions instantly and allows repetition. We’re eager for the results of this multi-year study.”
The study tackles contrails’ hidden downsides, like their heat-trapping potential, and advances cleaner fuel options. PACIFIC could assist to steer aviation toward a greener future, reducing both air quality issues and climate change contributions.
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