The impact of flying extends further than CO2 emissions. On top of carbon dioxide, aircraft engines emit other gases – nitrous oxides, sulfur dioxide and water vapour – and particulate matter (soot). These emissions have a climate impact, commonly referred to as non-CO2 effects, estimatedto account for two-thirds of the climate impact of flying.
The bulk of aviation’s non-CO2 effects is driven by the aromatics contained in conventional fossil jet fuel. The combustion of these molecules result in soot particle emissions responsible for the formation of persistent contrails, which have an important warming effect. However, these effects are very short lived compared to the impact of carbon dioxide, meaning that tackling non-CO2 effects could be the fastest way to reduce aviation’s climate impact.
Worse still, these emissions affect human health. The aromatics and sulphur contained in conventional jet fuel trigger ultrafine particle emissions, whose serious health impact is now widely acknowledged by the scientific community. Up to 33 million people living within a 20km radius of the top-20 airports in Europe are facing higher risks of high blood pressure, heart attack, and diabetes, due to air pollution induced by aviation particle emissions.
Despite being known for decades, non-CO2 effects and air quality issues from aviation have only recently started to receive more attention from industry and policy makers. As a result, precious years were lost in the fight to reduce the climate impact of aviation, and the lives of millions of European citizens were put at risk.
Fortunately, effective solutions exist to mitigate these effects. These include cleaning up the fuel we use in planes to reduce their aromatic and sulphur content, as they are the main drivers of particle emissions which affect the climate and air quality.
This can be done thanks to a well-established refining process called hydrotreatment. This process consists of adding hydrogen to refinery products at a certain temperature and pressure to modify their composition, and is already commonly used to produce road diesel.
Hydrotreatment could meaningfully reduce the aromatic content of jet fuel, whilst remaining in line with jet fuel safety standards set by the American Society for Testing and Materials (ASTM), which prescribes an 8% minimum aromatic content for aviation kerosene to ensure compatibility with current engines and fuel tank systems. That would still be a 200% decrease in aromatic content, which is currently on average at 15-20%. In the long term, original equipment manufacturers should be encouraged to develop engines that are compatible with 0% aromatics.
From an economic point of view, the preliminary findings from a forthcoming study by the International Council on Clean Transportation (ICCT) estimate that hydrotreated fuels would be about five percent more expensive than conventional jet fuel and would result in a ticket price increase of less than one percent. This seems like a small price to pay compared to the climate and health benefits induced by hydrotreated fuels.
From a legal perspective, non-CO2 effects, initially absent from the EU’s Fit for 55 package, were eventually included in the RefuelEU initiative, which should set up a Monitoring, Verification and Reporting (MRV) scheme to monitor the level of aromatics, naphthalene and sulfur in jet fuel. Additionally, it turns out that Sustainable Aviation Fuels (SAFs), mandated by ReFuelEU, will have a positive impact on air quality, as SAFs usually have a very low aromatic and sulphur content. However, their uptake will be slow. In the meanwhile, the EU needs to set up more ambitious policies to improve jet fuel quality. The ReFuelEU MRV should serve as a baseline for future binding legislation, including a European mandate for the gradual reduction of aromatic and sulphur contents in jet fuel.
All in all, with a solid body of research, an efficient short-term technology already available, non-prohibitive costs, and promising legislative pathways ahead, industry and lawmakers have no more excuse to leave non-CO2 effects on the shelf. It is high time we pick up the social and environmental benefits of this low hanging fruit.
T&E’s webinar on the importance of aviation fuel quality brought together industry, policymakers and researchers, who showed that tackling non-CO2 effects and air pollution through an improvement of jet fuel quality was not only technically, economically and legally feasible, but that it was also a climate and health imperative. Watch the recording to find out more.