Press Release 95-74
NSF Scientists to Study Airborne Particles That May Be Cooling Earth

October 31, 1995

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Scientists now suspect that increasing numbers of small particles of sulfur compounds and other pollutants floating in the atmosphere may affect so-called greenhouse warming in heavily industrialized regions. By reflecting sunlight back to space, these tiny airborne particles, called aerosols, can cool the earth beneath.

To learn more about "background" aerosols -- the naturally occurring counterparts to these pollutants - researchers from eight universities and the National Science Foundation (NSF)-supported National Center for Atmospheric Research (NCAR) in Boulder, Colorado are flying to the remote skies of Tasmania, with stops in Alaska, Hawaii, and other sites along the way. Flight operations for detailed studies of "clean" ocean air in the Southern Hemisphere will be based at Hobart, Tasmania, and take place from November 15 to December 14, 1995.

More than 100 scientists from 57 institutions representing Australia, France, Germany, Italy, Japan, the Netherlands, New Zealand, Sweden, the United Kingdom, and the United States are participating in this major study of airborne particles.

"Existing theories suggest that it should be very hard to create new particles in the lower atmosphere, yet they keep showing up," says researcher Barry Huebert of the University of Hawaii at Honolulu. "We're deploying stateof- the-art instruments to the remote marine atmosphere for the first time to seek the source of these new particles. This is the largest and most comprehensive experiment on natural background aerosols that we have ever done." Among the high- tech instrumentation will be NCAR's dualwavelength airborne lidar, which will map the vertical extent of aerosol layers in the atmosphere. Experiments will be conducted from a fully equipped C-130 research airplane owned by NSF and operated by NCAR.

Researchers aboard the C-130 will spend as many flight hours taking measurements during the two-week trip from the north Alaska coast to south of New Zealand as they will during the operations in Tasmania. In Alaska, they will begin their research measurements with a flight toward the North Pole and back. While in Hawaii November 5 and 6, the C-130 will fly through the Kilauea volcano plume to study how its particles form and how much sunlight they reflect. After arrival at Hobart, a flight toward the South Pole will complete the study's nearly pole-to-pole measurements.

Called ACE-1, the study is the first of the Aerosol Characterization Experiments, a series of international field programs to help scientists understand the chemical, physical, and optical properties of aerosols; how they form and grow; and their effect on radiation and climate.

Like carbon dioxide, sulfate aerosols are produced by human activity, mainly the burning of fossil fuels. They also exist naturally as sulfur emissions from living organisms and volcanoes. By scattering incoming solar energy back to space, both the natural and pollutant aerosols directly affect the amount of radiation entering the earth's atmosphere. They also serve as tiny sites on which water vapor can condense, allowing more small droplets to form within a cloud. This change in the droplets' size distribution makes the cloud more reflective, bouncing more solar radiation back to space and cooling the earth below.

In ACE-1, scientists will study the natural marine system -distant from Northern Hemisphere sulfate aerosols produced by human activity. ACE-2, scheduled for 1997, will focus on the marine atmosphere near European industrialized areas. As scientists learn more about aerosols naturally occurring in the undisturbed atmosphere, they can better assess the growing influence of humanproduced sulfate aerosols on climate.

"Until recently all climate models have supposed that the only human activity driving climate change was the production of carbon dioxide and other greenhouse gases," explains scientist Tom Wigley of NCAR. "We now believe that other factors, particularly sulfate aerosols, may be as important as greenhouse gases."

-NSF-

Media Contacts
Cheryl L. Dybas, NSF (703) 292-8070 cdybas@nsf.gov

Program Contacts
Jewel Prendeville, NSF (703) 306-1521 jprendev@nsf.gov

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering, with an annual budget of $6.06 billion. NSF funds reach all 50 states through grants to over 1,900 universities and institutions. Each year, NSF receives about 45,000 competitive requests for funding, and makes over 11,500 new funding awards. NSF also awards over $400 million in professional and service contracts yearly.

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