By collecting and analyzing the contrails created by planes running on a biofuel mix, a NASA study has found that biofuels can cut particle emissions by as much as 70 percent. The benefits come not just from reducing carbon emitted directly into the atmosphere but by also cutting down the chance of contrails forming, which can have an even bigger impact on the Earth's atmosphere.
According to the Air Transport Action Group (ATAG), aircraft were responsible for producing over 780 million tonnes of CO2 in 2015. To try to reduce that footprint, the industry is improving the efficiency of its jet engines, looking at alternate flight paths, and increasingly, turning to biofuels. Made from various plant material, including the hardy halophyte, camelina or waste from the forestry industry, biofuel-powered planes have been making the rounds from the likes of United Airlines, Virgin Atlantic and the US Air Force.
To investigate the effects of using biofuels, NASA and agencies in Germany and Canada ran a series of tests as part of the Alternative Fuel Effects on Contrails and Cruise Emissions Study (somehow shortened to ACCESS). A DC-8, running on a 50-50 blend of standard jet fuel and a biofuel derived from camelina oil, was flown in several tests in 2013 and 2014, while research aircraft trailed it at distances of between 300 ft (91 m) and 20 miles (32 km). These trailing craft measured not just the carbon emitted in the exhaust, but how contrails formed in the wake of the plane.
Before you whip out your tinfoil hat, note that we're not talking about the conspiracy theory of chemtrails – contrails are formed when the hot exhaust from aircraft engines meets the chilly high-altitude air, and are mostly made up of water vapor and ice crystals. But they are still problematic, since they're thought to sometimes spread out into artificial cirrus clouds that can disrupt natural weather processes. In fact, contrails are believed to have a larger impact on the planet's atmosphere than all the aviation industry's carbon dioxide emissions since the beginning of powered flight.
And that's where biofuels can help. The ACCESS tests found that the biofuel mix reduced particle emissions by between 50 and 70 percent, which is good news not just for CO2 air pollution, but for cutting back the likelihood that contrails will form.
"Soot emissions also are a major driver of contrail properties and their formation," says Bruce Anderson, a scientist on the ACCESS project. "As a result, the observed particle reductions we've measured during ACCESS should directly translate into reduced ice crystal concentrations in contrails, which in turn should help minimize their impact on Earth's environment."
NASA plans to continue to study the benefits of biofuels, and will demonstrate them with the supersonic X-plane, QueSST.
The research was published in the journal Nature.