Aviation’s contribution to climate change has recently been reassessed and shown to be substantially bigger than the warming effect of carbon dioxide alone, at a time when demand for air transport is expected to continue to grow. We now know that emissions, such as NOx and non-volatile particulate matter (nvPM), contribute to these non-CO2 climate impacts, the most important of which is atmospheric warming from contrails.
However, even this groundbreaking research only gives best estimates with substantial uncertainty ranges for the magnitude of these climate impacts, highlighting the urgent need for more understanding in order to effectively tackle them. Within this context, UNIC has identified key knowledge gaps that the project aims to address:
Aircraft engines are certified to meet NOx and nvPM limits that were developed in the 1980s to improve local air quality on the ground, and therefore cover only emissions measured during landing and take-off (LTO).
Aircraft engines are certified to meet NOx and nvPM limits that were developed in the 1980s to improve local air quality on the ground, and therefore cover only emissions measured during landing and take-off (LTO). This means there is little direct information on their exact levels during the longer cruise portion of a flight, where their impacts on climate occur. Cruise emissions are most often estimated, and even when directly measured, require another aircraft flying closely behind the first one with the needed instrumentation, which is expensive and challenging. This extrapolation is often imprecise and non-linear. In response, UNIC will develop an onboard sensor to measure these emissions directly at the engine exit, eliminating the need for a second aircraft. In addition to this, simulated cruise conditions of around -50°C will be created in a bespoke low-temperature oxidation flow reactor to improve measurement accuracy. Additionally, ground tests will be used to study non-CO2 emissions produced by engines with different combustor technologies across their full power range.
Alternative aviation fuels (SAF) and hydrogen (H2) will play a pivotal role in powering the decarbonized air transport system of the future.
Alternative aviation fuels (SAF) and hydrogen (H2) will play a pivotal role in powering the decarbonized air transport system of the future. As their use grows in the coming decades, so will the need to understand the full effect of their adoption. True to its mission to reduce uncertainty and enable action, UNIC will use the tools it develops to improve knowledge of the total climate benefits of both these fuels by going beyond carbon dioxide. This will involve testing or simulating their impact on non-CO2 emissions, both during test flights and ground experiments.
The role of volatile particulate matter (vPM) and vented engine oil vapor in contrail formation are currently poorly understood, and hence there is an urgent need to identify their climate effects to enable mitigation measures to be explored.
The role of volatile particulate matter (vPM) and vented engine oil vapor in contrail formation are currently poorly understood, and hence there is an urgent need to identify their climate effects to enable mitigation measures to be explored. Studies focusing on vPM formation are limited. Nitric acid and oil vapors are key contributors to vPM.
Another climate impact that remains largely unknown is the interaction between aerosols from jet engine emissions and clouds existing in the atmosphere
Another climate impact that remains largely unknown is the interaction between aerosols from jet engine emissions and clouds existing in the atmosphere: there is uncertainty on whether naturally occurring clouds are perturbed by these emissions in a way that results in a net warming or cooling effect. UNIC’s insight from measuring volatile particulate matter emissions (vPM) will be instrumental in better modeling these interactions and representing them in global climate models.