By trailing extremely closely behind an aircraft, NASA pilots may have helped find a way to cut particle emissions from planes by up to 70 percent, a discovery that could greatly reduce their effect on the climate, new research shows.
To conduct their study, published this week in the weekly science journal Nature, a team of scientists led by the United States space agency put a 50-50 blend of normal jet fuel and biofuel into a NASA DC-8 aircraft and then flew small chase planes fitted with instruments 100 to 500 feet behind them to measure the emissions.
The burning of cleaner fuel alone would have a positive impact on the environment, with annual air travel releasing nearly 800 million metric tons of CO2 into the atmosphere every year. But more than that, the study found the reduction in particle pollution reduced the contrails, which trap heat below them and can increase temperatures beneath up to 10 degrees celsius.
[Editor's note: The preceding paragraph has been updated to correct an erroneous conversion from Celsius to Fahrenheit.]
"Those soot particles serve as nuclei for water vapour in the very cold atmosphere to condense on and for the artificial-looking linear contrails that we see when we look out the window," Richard Moore from NASA's Langley Research Center, and who led the research team, told the BBC World Service’s Science In Action program. "You’ll then see those lines spread and form cirrus clouds that weren't there before the plane flew through the airspace.
"We know these contrails and cirrus clouds have a warming effect on the Earth's climate, and it's currently thought the warming effect associated with those clouds is more significant than all of the carbon dioxide emitted by aviation since the first powered flights began.”
Previous studies on the effect of jet fuel had been conducted on a grounded jet by locking it down and throttling up its engines, but scientist wanted to see how the particles interacted with the far colder air at cruising altitudes between 30,000 and 40,000 feet.
To ensure they were only measuring pollution from the contrails of the aircraft they were following, scientists flew between 30 meters (98 feet) and 150 meters (492 feet) behind the aircraft. The study found it cut the amount of black carbon 50 percent by number and 70 percent by mass.
The 50-50 jet-fuel burned by the DC-8's four engines was “a renewable alternative fuel of hydro processed esters and fatty acids produced from camelina plant oil,” according to a NASA press release.
While the promising results may suggest it would be logical to only use biofuels, Dr. Moore said a number of engineering and infrastructural limitations, including some jet engines needing a certain quota of traditional jet fuel to function safely, meant that wasn't currently possible, according to the BBC.