Zooming In On Non-CO2 Effects Of Aircraft Emissions

With the contribution of aviation’s carbon dioxide emissions to global greenhouse gas emissions now well known—and efforts underway to reduce it—attention is increasing on the non-CO₂ emissions that can have a considerable effect on both the environment and public health.

Non-CO₂ emissions—from water vapor that can form condensation trails (or contrails) to nitrogen oxides, sulphur oxides, carbon monoxide and ultrafine particles (UFP)—are the focus of many initiatives to understand their effects and how to minimize them.

• Contrail avoidance can reduce non-CO₂ effects
• Hydrotreatment can cut standard kerosene’s non-CO₂ emissions
• T&E study highlights ultrafine particle risk for airport neighbors

One major tool in reducing non-CO₂ effects from flying is the increased adoption of sustainable aviation fuel (SAF). The first inflight study of emissions from a commercial aircraft using 100% hydroprocessed esters and fatty acids (HEFA)-based SAF in both engines recently confirmed a reduction in contrail formation compared with conventional Jet A-1 fuel.

Under the ECLIF3 (Emission and Climate Impact of Alternative Fuels) study conducted by Airbus, German aerospace center DLR, Rolls-Royce and SAF producer Neste, the two Airbus A350-900, Rolls-Royce Trent XWB-84-powered flights in April 2021 were also the first to measure contrails from combustion of 100% SAF.

“We already knew that sustainable aviation fuel could reduce the carbon footprint of aviation,” Mark Bentall, Airbus head of research and technology, said in June. “Thanks to ECLIF studies, we now know that SAF can also reduce soot emissions and ice particulate formation that we see as contrails.”

But with SAF volumes still a small proportion of aviation’s overall fuel use, industry must prioritize better understanding non-CO₂ emissions, their effects and ways they can be minimized.

Airlines are keen to explore operational steps, and contrail avoidance could play an important role. Contrail Pilots—a consortium convened by the Bill Gates-founded nonprofit Breakthrough Energy including seven airlines as well as weather, flight-planning and research specialists—is seeking European Union funding for a large-scale contrail mitigation trial that aims to cover 18,000 flights over four years.

Contrail Pilots is waiting to hear whether it has won a €9 million ($9.6 million) grant from the EU Innovation Fund, which channels money raised from the EU Emissions Trading System (ETS) into environmental projects.

Safran in June invested in Estuaire, a Paris-based startup offering software tools to measure and reduce aviation’s climate impact, with a focus on contrail prevention. The company’s flight data analytics platform integrates radar flight tracks, numerical weather predictions, passenger load factors and several climate and flight physics models.

European ETS legislation approved last year includes a mechanism for monitoring non-CO₂ effects. Leading on from that, policymakers plan to have a legislative proposal on non-CO₂ effects ready by 2027. In addition, the recent Ambient Air Quality Directive (AAQD) mandates monitoring of UFP.

Both advances are good but not good enough, according to Brussels-based nonprofit Transport & Environment (T&E).

“I think the fact that ultrafine particles as a pollutant have been recognized in the AAQD as something that deserves attention from the member states is a big step,” T&E aviation policy manager Krisztina Toth tells Aviation Week. “Obviously the pace that things are proceeding is not what we would like to have, but it’s a step in the right direction.”

In June, T&E released a report on research by Netherlands-based environmental consultancy CE Delft exploring the potential UFP health risks for people who live near airports.

UFP are approximately 1,000 times smaller than a human hair and capable of penetrating deep into the human body. They are linked with heart, respiratory and neurological conditions, as well as pregnancy issues and other problems.

“There is a strong need to analyze the impact of this tiny pollutant, which is today under-researched, overlooked [and] not monitored systematically, but with potential high impact on air quality and human health,” T&E aviation technical manager Carlos Lopez de la Osa said during a briefing ahead of the study’s release.

T&E recommended installing sampling points in and around airports in European member states to quantify UFP concentration levels more accurately, with a view to introducing UFP target values in the next revision of the AAQD.

Beyond better monitoring of UFP, T&E is calling for more hydrotreatment, a process that can reduce the UFP emissions of standard kerosene—at a cost of around 5 cents per liter, the nonprofit says—as industry awaits greater volumes of SAF, which emits fewer UFP.

Contrail avoidance combined with kerosene hydrotreatment could have a big impact while only increasing ticket prices by around 1%, Lopez de la Osa tells Aviation Week.

“These are two solutions that are within reach,” he says. “They are not going to massively affect the aviation sector but can offer a great opportunity to mitigate the climate effects of aviation in double digits.”

T&E also wants a ban on expanding airport infrastructure, the introduction of flight caps, the promotion of a shift to rail, a reduction in business travel, targeted taxation of the aviation sector and the creation of a jet fuel standard, including a progressive reduction of aromatics and sulphur, paving the way to SAF without them altogether.

The CE Delft study uses UFP concentration levels around Amsterdam’s Schiphol Airport and extrapolates them to Europe’s main airports. It estimates that 280,000 cases of high blood pressure, 330,000 of diabetes and 18,000 of dementia may be linked to UFP emissions among the 51.5 million people living around Europe’s 32 busiest airports.

“This is a first estimation of what the impacts could be, and more epidemiological research should be done to give a more exact estimation,” Daan van Seters, CE Delft researcher and report co-author, said during a June 20 briefing.

“What is important to realize is that these are big numbers,” co-author Stefan Grebe added. “This study indicates that it is really worth looking into it. It might be higher or it might be lower, but it is something that should be researched, because potentially it has very huge effects on health.”