Trace gas study accumulates 40 million frequent-flyer miles for science

At any given moment about 4000 commercial aircraft are flying over the Earth. To an atmospheric scientist they constitute a potentially vast array of in situ measurement platforms, an obvious source of high-resolution upper tropospheric/lower stratospheric (UT/LS) trace gas data that could not be obtained on such a continuous basis in any other way, especially over the oceans. The number of flights has been steadily growing, and the long-term outlook for continued "funding" looks excellent given the penchant for humans to travel around the world. And yet, to date, there have been few attempts to tap this resource for atmospheric chemistry studies. One study, however, has chalked up 40 million miles over the past five years.

Using commercial airliners to measure trace gases in the atmosphere is a well-justified self-monitoring activity, since engine exhaust is constantly injecting material into the flight corridors. Although the total amount is not great (2 to 3% of all anthropogenic atmospheric pollution), the UT/LS region is sensitive to aircraft emission in several ways. Nitrogen oxides, CO, and hydrocarbons through photochemical reactions may increase the amount of tropospheric ozone, which is a greenhouse gas; and water vapor, soot, and sulfur oxides can increase contrail clouds and aerosols that may modify UT/LS radiative forcing and the global temperature.

With air traffic expected to double in the next 10 to 15 years, aviation effects on the atmosphere can only be expected to increase as well. To take advantage of this existing atmospheric sampling infrastructure, a program to measure ozone and water vapor by Airbus in-service aircraft (MOZAIC) was launched in January 1993 [Marenco et al., 1998]. So far MOZAIC has recorded over 10,300 flights totaling 74,000 hours and 40 million miles. Initial scientific results were published in a special section of the Journal of Geophysical Research in 1998 (vol. 103, no. D19) as well as in other journals, including two papers in Nature.

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