BOULDER--Two research aircraft and 100 scientists and support staff areheading to the South Pacific to study what some have called the world'scleanest air. The March 10-April 30 flights are part of the secondPacific Exploratory Mission to the Tropics (PEM-Tropics B). Nineprincipal investigators from the National Center for AtmosphericResearch (NCAR) are participating in the mission, which is part of theGlobal Tropospheric Experiment sponsored by the National Aeronautics andSpace Administration (NASA). NCAR's primary sponsor is the NationalScience Foundation.
Researchers will gather data on the chemical species that affectformation of tropospheric ozone and sulfate aerosols. The goal is todetermine how well the earth's atmosphere cleanses itself. This chemicalprocess, called oxidation, includes removal of gases that wouldotherwise be warming the troposphere or causing stratospheric ozonedepletion. The tropics play a key role in determining the globaloxidizing power of the atmosphere because the high levels of humidityand ultraviolet radiation found there promote the formation of oxidizingmolecules.
PEM researchers aboard the NASA-Ames DC-8 jet and the NASA-Goddard P-3Bturboprop will measure hundreds of chemical species and compounds using35 instruments. The aircraft will be deployed from sites in Hawaii,Christmas Island, Tahiti, American Samoa, Easter Island, and Fiji tocover an area ranging roughly from the Cook Islands to the west coast ofSouth America. Over 30 principal investigators from 17 U.S. universitiesand research laboratories are involved in the experiment.
The chemistry of the tropical Pacific's troposphere (the atmosphere'slowest layer, which reaches an average height of 16 kilometers, or 10miles, over the tropics) was largely unknown until the PEM-Tropics Amission in 1996, when researchers took extensive measurements during theSouthern Hemisphere's dry season from August to October. They foundsignificant levels of human-generated pollution, primarily from firesset to clear land for agriculture in Africa and possibly South America.PEM-Tropics B is returning during the wet season, when the impact ofbiomass burning in the Southern Hemisphere is expected to be much lower.
"We will have so many airborne instruments taking measurements thatwe'll be able to draw some conclusions about the chemistry of sulfateaerosols and the chemistry that's responsible for production and loss oftropospheric ozone," explains NCAR scientist Brian Ridley. The abilityof sulfate aerosols to reflect the sun's radiation may be one reasonthat increasing greenhouse gases have not warmed the earth as much assome climate models have predicted. Sulfates also contribute to localpollution and acid rain. While the sources of tropospheric ozone includebiomass burning and urban smog, this trace gas is also involved in theoxidizing process. Understanding the life cycle of ozone in thetroposphere is vital to understanding the oxidizing capacity of theatmosphere.
A virtual field expedition for kids
NCAR scientist Lee Mauldin is creating a Web site for the PEM missionaimed at K-12 students around the world (http://www.acd.ucar.edu/pem).He'll provide twice-weekly updates on what it's like to do science overthe South Pacific. Mauldin will post photos of the mission in action; alink to his electronic mailbox will allow students to ask questions andsee answers on the site. Contact him at email@example.com.
NCAR is managed by the University Corporation for Atmospheric Research,a consortium of more than 60 universities offering Ph.D.s in atmosphericand related sciences.
Writer: Zhenya Gallon
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