The Problem....
Microscopic atmospheric aerosol particles can cool the Earth's surface by reflecting sunlight back into space. When present in large quantities, these particles form a visible haze. Many of the larger particles can form cloud droplets which also reflect incoming solar radiation. Although atmospheric aerosols are chemically complex and may be influenced strongly by local emissions, one consistent feature, world-wide, is a strong presence of sulfate. Before the industrial period these particles were formed from sulfur gases emitted from the ocean and volcanoes. Today, the major source of atmospheric sulfate particles is the sulfur dioxide emitted from fuel combustion by power plants and industry.
It is difficult to calculate the effect of aerosol particles on
the Earth's climate because of a lack of globally distributed
data and a clear understanding of the processes that link gas
emissions with particle formation and growth. Present estimates
of the cooling over industrial regions (eastern USA, Europe, eastern
Asia) due to the sulfate haze alone is slightly greater on a regional
basis than the warming due to greenhouse gases produced by human
activities. However, the uncertainties in these estimates are
very high. Estimates of the cooling which results from aerosols
forming additional cloud droplets are even more uncertain.
The International Global Atmospheric Chemistry Program (IGAC)
has planned a series of experiments to better understand the chemical,
physical, and radiative properties of atmospheric aerosols and
the processes which control these properties. The goals of these
Aerosol Characterization Experiments (ACE) are to provide the
necessary data to incorporate aerosol particles into global climate
models and to reduce the overall uncertainty in calculating the
climatic effect of aerosols.
The experiment involved scientists from 44 research institutions
in 11 countries and included measurements from the NCAR C-130,
the NOAA research vessel Discoverer , the Australian fisheries
research vessel Southern Surveyor, and land-based stations at
Cape Grim and Macquarie Island, Australia and Baring Head, New
Zealand. Observations from these six platforms will be compared
with simultaneous satellite measurements to test and improve models
of sunlight reflection by atmospheric particles.
The Benefits...
The experiment will provide data on:
ACE-1 is the first in a series of experiments. The understanding
gained in ACE-1 will be used to study progressively more complex
environments. ACE-2 will extend these studies to the North Atlantic
Ocean and focus on the anthropogenic aerosols from the European
continent and desert dust form the African continent.
ACE-1 was conducted from 15 November to 14 December 1995 over
the Southwest Pacific Ocean, South of Australia and involved the
joint efforts of the International Global Atmospheric Chemistry
Project's (IGAC) Aerosol Characterization and Process Studies
(ACAPS) Activity and Marine Aerosol and Gas Exchange (MAGE) Activity.
The U.S. National Science Foundation (NSF), Atmospheric Chemistry
Program
The U.S. National Oceanic and Atmospheric Administration (NOAA),
Office of Global Programs
The U.S. National Aeronautical and Space Administration (NASA)
The Australian Commonwealth Scientific and Industrial Research Organization (CSIRO)
The Australian Bureau of Meteorology (BoM)
The Australian Antarctic Division (ANARE)
The New Zealand National Institute for Water and Atmospheric Research (NIWA)
The first experiment, ACE-1, took place in the minimally polluted
marine atmosphere south of Australia. Non-sea-salt sulfate aerosol
particles in the remote marine atmosphere are thought to have
only one primary gaseous precursor, dimethlysulfide (DMS), thereby
simplifying studies involving the formation and growth of the
aerosol. This marine environment also afforded an opportunity
to study the properties of natural aerosols and thus provides
a background from which to compare and quantify any human induced
changes.
These data will be used to test regional and global aerosol climate
models and thus produce more accurate assessments of the climatic
effect of aerosol particles. The net result will be more accurate
predictions of climate change. Since climate change may cause
some regions to become more arid while others experience more
frequent flooding, heavier snowfall or more severe storms, the
ability to accurately predict regional climate changes will have
a tremendous economic impact.
Major funding for ACE-1 has been provided by:
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