BOULDER--Two research aircraft and 100 scientists and support staff are heading to the South Pacific to study what some have called the world's cleanest air. The March 10-April 30 flights are part of the second Pacific Exploratory Mission to the Tropics (PEM-Tropics B). Nine principal investigators from the National Center for Atmospheric Research (NCAR) are participating in the mission, which is part of the Global Tropospheric Experiment sponsored by the National Aeronautics and Space Administration (NASA). NCAR's primary sponsor is the National Science Foundation.
Researchers will gather data on the chemical species that affect formation of tropospheric ozone and sulfate aerosols. The goal is to determine how well the earth's atmosphere cleanses itself. This chemical process, called oxidation, includes removal of gases that would otherwise be warming the troposphere or causing stratospheric ozone depletion. The tropics play a key role in determining the global oxidizing power of the atmosphere because the high levels of humidity and ultraviolet radiation found there promote the formation of oxidizing molecules.
PEM researchers aboard the NASA-Ames DC-8 jet and the NASA-Goddard P-3B turboprop will measure hundreds of chemical species and compounds using 35 instruments. The aircraft will be deployed from sites in Hawaii, Christmas Island, Tahiti, American Samoa, Easter Island, and Fiji to cover an area ranging roughly from the Cook Islands to the west coast of South America. Over 30 principal investigators from 17 U.S. universities and research laboratories are involved in the experiment.
The chemistry of the tropical Pacific's troposphere (the atmosphere's lowest layer, which reaches an average height of 16 kilometers, or 10 miles, over the tropics) was largely unknown until the PEM-Tropics A mission in 1996, when researchers took extensive measurements during the Southern Hemisphere's dry season from August to October. They found significant levels of human-generated pollution, primarily from fires set to clear land for agriculture in Africa and possibly South America. PEM-Tropics B is returning during the wet season, when the impact of biomass burning in the Southern Hemisphere is expected to be much lower.
"We will have so many airborne instruments taking measurements that we'll be able to draw some conclusions about the chemistry of sulfate aerosols and the chemistry that's responsible for production and loss of tropospheric ozone," explains NCAR scientist Brian Ridley. The ability of sulfate aerosols to reflect the sun's radiation may be one reason that increasing greenhouse gases have not warmed the earth as much as some climate models have predicted. Sulfates also contribute to local pollution and acid rain. While the sources of tropospheric ozone include biomass burning and urban smog, this trace gas is also involved in the oxidizing process. Understanding the life cycle of ozone in the troposphere is vital to understanding the oxidizing capacity of the atmosphere.
A virtual field expedition for kids
NCAR scientist Lee Mauldin is creating a Web site for the PEM mission aimed 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 over the South Pacific. Mauldin will post photos of the mission in action; a link to his electronic mailbox will allow students to ask questions and see answers on the site. Contact him at mauldin@ucar.edu.
NCAR is managed by the University Corporation for Atmospheric Research, a consortium of more than 60 universities offering Ph.D.s in atmospheric and related sciences.
Writer: Zhenya Gallon
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