UCAR > Communications > UCAR Quarterly > Winter 2001 Search

Winter 2001

Preliminary results from ACE-Asia

by Zhenya Gallon

Barry Huebert, principal investigator for the Asian Pacific regional expedition of the Aerosol Characterization Experiments, visited NCAR's Research Aviation Facility in October and gave an overview of preliminary findings from the big international field campaign that took place this past spring (see On the Web, below). ACE is part of International Global Atmospheric Chemistry, a core project of the International Geosphere-Biosphere Programme.

The main goals of this ACE project are to characterize the chemical composition of Asian aerosols, assess their optical properties, and thereby provide realistic data on the physical, chemical, and radiative properties of Asian aerosols for numerical climate modeling. The expedition, scheduled to coincide with the spring dust storms that typically arise from the Mongolian and western Chinese deserts, included extensive observations of a large storm that began on 5 April. An excellent example of intercontinental aerosol transport, this storm's radiative effects were noted days later in many places across the United States (see On the Web, below). Measurements by NOAA researchers over Colorado suggest that the gas-phase pollutant carbon monoxide was also transported thousands of kilometers with the dust.

During the campaign, ACE-Asia flight planners used output from three different chemical transport models to predict where the most interesting concentrations of dust and pollution would be. For the large storm, it was 11 April by the time its winding path crossed the Asian continent and emerged at the Yellow Sea. "We were able to plan our flights to hit this just as it came off the coast," said Huebert, thanks to the chemical transport model forecasts.

Sometimes, however, political considerations prevented the aircraft and the NOAA research vessel Ron Brown from reaching air masses. "We had a very narrow corridor in the Yellow Sea that we were allowed to operate in, between the South Korean military warning areas to the east and Chinese airspace to the west. But I still think we got a terrific data set, even though we were pretty restricted," Huebert said.

The new low turbulence inlets on the NSF/NCAR C-130 aircraft performed well, Huebert reported. The enhanced capture of large particles by the inlets will be calculated so that measurements from the instruments behind the inlets can be corrected to ambient concentrations.

There were extensive measurements of organic aerosols on the C- 130 flights. For many samples, there was less organic carbon than sulfate, but for others, including many at high altitudes, the reverse was true. "We need to make sure in future programs that we're measuring the organic part as well as the more easily measured sulfate," said Huebert.

It turned out that the soluble chemical composition of the dust was dominated by calcium, sulfate, and nitrate. Preliminary numbers show soluble calcium alone was 120–130 micrograms per cubic meter near the source of the largest dust storm.

The dust plume off of Qingdao, China, yielded insights about the radiative properties of dust particles. Most of the light absorption measured by a University of Washington group came from small particles of less than 1 micron. "That means that the soot, which is the primary absorber here, may have been mixed a little bit with the dust, but most of the soot was in its own separate small-particle mode. The soot about doubled when we went into the Qingdao plume." In contrast, light scattering was almost all due to particles larger than 1 micron.

Experimenters were also interested in water uptake by particles and changes in light scattering as a result. They found distinctly different extinction of sunlight as it encountered various combinations of dust, anthropogenic pollution, and sea salt particles. Dust exhibited far less water uptake than the other aerosols as humidity increased. "That's one of the ways that the dust really is qualitatively different from the air pollution aerosols."

The ACE-Asia science team is now at work reducing data in preparation for a special issue of the Journal of Geophysical Research.

On the Web:
ACE-Asia participants and platforms
"Ace-Asia finds plenty to study," background from the UCAR Quarterly
UCAR Joint Office for Science Support field campaign Web pages
Mid-April dust storm: "President's Corner," UCAR Quarterly

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UCAR > Communications > UCAR Quarterly > Winter 2001 Search

Edited by Bob Henson, bhenson@ucar.edu
Prepared for the Web by Jacque Marshall
Last revised: Thu Dec 20 16:42:17 MST 2001