【気候科学】バイオ航空燃料による微粒子排出量の削減

A blend of conventional fuel and biofuel reduces particle emissions from aircraft engines at cruise conditions by 50 to 70 per cent compared to conventional fuel, reports a study in this week’s Nature. The findings provide important data on the environmental impact of biofuel use by aircraft in-flight, which have not previously been reported, and may be valuable in assessing the potential of aviation biofuels as a viable strategy to mitigate climate change.

Aerosols released by aircraft engines contribute to the formation of clouds (in the form of contrails), which can affect the climate via their interaction with radiation from sunlight and by changing how much water is stored in the atmosphere. Sustainable biojet fuels are being assessed for their potential to reduce emissions, but previous tests have been ground-based, where engine operating conditions are very different to those in-flight.

Richard Moore and colleagues report airborne measurements of emissions from a test aircraft whose four engines were fed either conventional Jet A fuel, or a blend of Jet A and biofuel (derived from Camelina oil). The observations were made from research aircraft that trailed around 30-150 metres behind the engines, flying at altitudes of 30,000-36,000 feet (9,140-10,970 metres). The biofuel blend produced notably lower aerosol emissions than did conventional fuel, although the reduction was less pronounced at high-thrust settings compared to low- and medium-thrust settings. The experiments also provide information about the kind of aerosol particles emitted that can help modelling studies to assess whether the use of aviation biofuels is a feasible strategy to help to mitigate climate change.