Scientists look for signs of pollution in the superhighway in the sky

October 05, 1999

If you think traffic is getting worse on your commute, you're not alone. Hundreds of commercial airline flights carry thousands of passengers from the U.S. to Europe each day-traveling along what has become the busiest jet super highway in the world: the Atlantic corridor. Could all of that air traffic exhaust be a detriment to the atmosphere at 35,000 feet the way that auto exhaust pollutes the air we breathe?

In a study to be released in the Oct. 15 issue of the journal Geophysical Research Letters, NASA scientists found that the atmosphere over the Atlantic acts nothing like the Los Angeles basin when it comes to collecting ozone-the chemical responsible for smog.

The key chemical in creating ozone is nitric oxide, a byproduct of aircraft and rocket exhaust, said Dr. Anne Thompson, a Goddard Space Flight Center (Greenbelt, Md.) atmospheric scientist who led the study as part of NASA's Atmospheric Affects of Aviation Experiment. Increasing the amount of nitrogen oxides increases the amount of ozone. "When we cross the jet tracks an hour after they pass by, it's easy to find their chemical trail," said Thompson. But when the scientists looked for increased levels of smog chemistry covering the entire flight corridor, they couldn't find them, she said.

What complicated the gas analyses is that ozone and nitrogen oxides have several ways of working their way six miles up into the atmosphere. The gases can come from below, when man-made smog is funneled up during a thunderstorm. Ozone can meander down from the stratosphere where it acts as Earth's ultraviolet shield. And nitrogen oxides in large amounts can be produced on the spot by lightning strikes. So it becomes very difficult to unequivocally pin down where the nitrogen oxides and ozone are coming from.

Another critical ingredient complicating the November 1997 study was the year's powerful El Niño. Thompson found that on the eastern side of the Atlantic, clean air made aircraft exhaust easy to find. But over Maine and Canada, nitrogen oxides from summer-like thunderstorms and lightning swamped the aircraft signal, leaving scientists to wonder how typical their sampling period was.

Since ozone at 35,000 feet can't hurt your lungs or make your eyes water, why do scientists care about air quality there? According to Thompson, when ozone gets that high up, it starts to act like a greenhouse gas and can contribute to global warming. "So knowing how airliners and rockets add to the picture is important for climate research," she said.

In the Fall of 1997, the scientists in the Subsonic Assessment Ozone and Nitrogen Oxides Experiment (SONEX) set out to see if the high volume of airline travel was helping heat up the globe. The team flew for more than 100 hours from Bangor, Maine, Azores and Shannon, Ireland in a specially equipped NASA DC-8, collecting samples of the air's chemistry.

In the end, Thompson said, the findings showed that jet aircraft, which burn very "clean," fuel, probably added a few tens of parts per trillion of nitrogen oxides to the atmosphere. That's the equivalent of adding 10 molecules of nitrogen oxides to a trillion molecules of air. But the air that far up is so clean, even such a small number of molecules could be an increase in nitrogen oxides of more than 20 percent, said Thompson.

For now, Thompson contends that ozone impacts along the Atlantic Corridor are too small to detect, but according to industry specialists, who indicate that the future holds a steady increase in air traffic, makes understanding the effects of air travel on the global climate increasingly important.
For more information on SONEX, visit the web site at:

See images at: FTP://

NASA/Goddard Space Flight Center

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