As the aviation sector continues to explore greener alternatives, researchers in the UK are examining the impact that sustainable aviation fuel (SAF) may have on both air quality and the climate — beyond its well-known carbon-reduction benefits.
A team from the National Centre for Atmospheric Science (NCAS), alongside partners from universities and aerospace organisations, is conducting pioneering work through a project known as GRIM-SAF (GRound-Based and Inflight Measurements). Their research focuses on emissions produced by aircraft engines running on different types of fuel, including SAF blends, with a particular emphasis on pollutants other than carbon dioxide.
Beyond CO₂: Why It Matters
While carbon dioxide often dominates discussions about aviation’s environmental footprint, it is far from the only pollutant produced by jet engines. Non-CO₂ emissions — such as soot, nitrogen oxides (NOx) and ultrafine particles — significantly influence local air quality around airports and contribute to what scientists call Effective Radiative Forcing, a measure of an emission’s impact on climate. In fact, non-CO₂ emissions can represent up to two-thirds of aviation’s total climate impact.
For communities situated near busy flight paths, exposure to these emissions can pose real public-health concerns. Ultrafine particles, in particular, have been detected kilometres downwind of major airports, raising questions about pollution exposure and longer-term health risks.
The GRIM-SAF Approach
Engine tests on static stands have allowed researchers to monitor emissions directly from jet engines powered by both conventional jet fuel and SAF blends. By using advanced sampling tools, the team aims to understand how SAF affects a variety of pollutants — from soot and sulphur dioxide to NOx and volatile organic compounds.
Their work is part of a larger effort to move beyond fuel-only carbon metrics and develop a holistic picture of aviation’s environmental impact. This includes considering how SAF might shift emission profiles and potentially improve local air quality as well as reduce climate warming.
Key Questions Still Being Answered
Although earlier studies have shown that SAF can significantly reduce carbon emissions — in some cases by up to 80% over its lifecycle — its influence on other pollutants is less well understood. SAF’s composition, which often contains fewer aromatics and lower sulphur content than traditional kerosene, could reduce soot and some particulates. However, impacts on nitrogen oxides and other less-studied compounds remain uncertain.
As researchers emphasise, burning SAF does not eliminate air pollution entirely. In certain operational phases, such as during taxiing or idle on airport grounds, inefficient fuel use can still generate emissions harmful to public health.
The Bigger Picture
The GRIM-SAF project reflects a growing scientific effort to move beyond simplistic measures of aviation’s environmental footprint. Researchers argue that addressing aviation’s total impact means accounting for all emissions — not just CO₂ — and understanding how alternative fuels can mitigate warming and improve air quality.
As electric vehicles and low-carbon transportation gain traction on the ground, aviation will increasingly make up a larger share of emissions like NOx. That reality underlines the importance of innovative research and collaboration between scientists, fuel developers and aviation stakeholders.
Looking Ahead
While SAF remains a promising path toward reducing aviation’s carbon footprint, its effectiveness in improving air quality and mitigating climate change depends on a nuanced understanding of how fuels alter non-CO₂ emissions. Projects like GRIM-SAF are crucial in closing knowledge gaps and enabling smarter policy, innovation and investment decisions.
As the aviation industry faces growing pressure to decarbonise and reduce its environmental footprint, research into SAF’s wider implications will play an important role in shaping the future of greener skies — one test flight and engine stand at a time.