Aviation Biofuels Might Just Work For Cutting Greenhouse Emissions

To measure the aerolsols emitted with different sorts of fuel, a research aircraft chased a DC8 plane that can switch fuels in flight across the sky. Richard Moore/NASA

Mixing biofuels in with jet fuels from fossil sources reduces particle emissions by 50 to 70 percent, a new study reports. The finding offers hope for tackling one of the most intransigent aspects of global warming.

Flying is a very climate-unfriendly way to get around. That's not just because it requires a lot of fuel to defy gravity, but because existing aircraft engines release aerosols, which contribute to cloud formation. Clouds can either warm or cool the planet depending on their height and density, but unfortunately the consequences of airplane aerosols are almost entirely in the wrong direction, producing just the sort of clouds we don't want. Ironically, these aerosols also, under certain weather conditions, produce the contrails that inspire bizarre conspiracy theories

Changing the fuel mix could reduce aerosol production in flight, so a team led by Dr Richard Moore of NASA's Langley Research Center set out to test a comparison between widely used Jet A fuel, a low-sulfur version, and a 50:50 mix of low-sulfur Jet A and a biofuel made from Camelina oil.

Working out how many aerosols are emitted is no easy task, but by having research aircraft trailing 30-150 meters (100-500 feet) behind a test DC8 plane while flying at heights around 10,000 meters (33,000 feet), Moore detected a dramatic drop in aerosol release, at least when cruising at constant velocity.

The findings have been published in Nature, where the authors describe the effects of switching between fuel tanks loaded with different fuel mixtures, allowing them to eliminate any differences based on engine. Nitrogen oxides aside, all aerosol types were reduced, often dramatically.

The aerosol reduction is attributed to the near total absence of sulfur and aromatics in aviation biofuels.

Air travel represents about 5 percent of humanity’s contribution to cooking the planet, but that's expected to grow. Most of the bigger ways we are changing the climate represent political rather than technical problems. We know how to drastically reduce carbon dioxide from the electricity sector, for example, however doing it is a matter of will. Stopping the destruction of tropical rainforests would be even easier if the desire was there.

On the other hand, flight is a rapidly growing industry as the world becomes more connected. Although more efficient engines can offer some reduction, biofuels are one of the few options to make the sort of changes that are needed without seriously affecting modern lifestyles.

Biofuels for land-based transport have generally failed to live up to their hype, sometimes releasing more carbon dioxide in their production than they offset. If Moore's work holds up, however, the story could be very different for aircraft, and biofuel production could be an industry set for take-off.

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