|
 C Irvine researchers who study the chemistry of ocean/air
interactions have discovered how airborne sea salt particles
may be involved in helping to determine the levels of some greenhouse
gases, as well as air quality, in coastal urban areas.
 In collaboration
with other molecular scientists, Barbara Finlayson-Pitts, a UCI
professor of chemistry, and Donald Dabdub, a UCI assistant professor
of mechanical and aerospace engineering, have been able to show
that sea salt particles - a common ingredient of coastal and
ocean air undergo a previously unrecognized chemical reaction
in daylight to release chlorine molecules, which can influence
ozone levels in the lower atmosphere. Their findings appear in
the April 14 issue of Science.
In sunlight,
these molecules decompose into highly reactive chlorine atoms.
When these atoms are formed in the presence of pollutants emitted
from fossil fuel energy sources, such as oil, coal and gasoline,
they may lead to the formation of ozone, which is recognized
as an air pollutant. Because ozone has documented health effects
at quite low levels, both state and federal authorities have
established quality standards for this pollutant.
"The
ocean is two-thirds of the earth's surface, so to understand
global climate issues and the chemistry of air pollution in coastal
regions, you need to understand the role of sea salt particles,"
Finlayson-Pitts said. "Our study suggests that sea salt
particles may be a factor that needs to be taken into account
in assessing levels of greenhouse gases and air pollutants such
as ozone in the air."
In this study,
UCI researchers observed the reaction of hydroxyl radicals (equivalent
to water, H2O, with a hydrogen atom removed) with tiny particles
composed of water and sodium chloride the basis of sea salts.
The hydroxyl radical is always present in air. The researchers
found unique chemical reactions on the surface of the sea salt
particles, rather than inside the particles as had been previously
observed.
Until now,
it was believed that a reaction between hydroxyl and sea salt
required that the hydroxyl radical be absorbed into the liquid
particle before reacting. It also was believed that chlorine
would not be formed unless the particles were acidic. Neither
of these two activities was observed in this study. The discovery
of hydroxyl reactions on the surface of sea salt particles further
suggests that the creation of atmospheric chlorine through sea
salt interaction may be greater than previously realized.
"This
finding implies that this unique chemistry occurring on sea salt
particle surfaces is yet another way of getting chlorine into
the air," Finlayson-Pitts said. "Because they're so
highly reactive, these chlorine atoms are important in the understanding
of the formation and the fate of a number of trace gases vital
to global climate issues."
In continuing
this research, Dabdub will introduce this information on sea
salt chlorine creation into a complex computer modeling program
that analyzes and predicts the air quality of the South Coast
Air Basin of California - a highly populated coastal area that
records some of the highest levels of air pollution in the United
States to see its impact on levels of ozone and other pollutants.
Participating
in this study with Finlayson-Pitts and Dabdub are Eladio Knipping
of UCI's Department of Mechanical and Aerospace Engineering;
Matthew Lakin, Krishna Foster, R. Benny Gerber and Douglas Tobias
of UCI's Department of Chemistry, and Pavel Jungwirth of the
J. Heyrovsky Institute of Physical Chemistry, Academy of Science
in the Czech Republic.
The study
was funded by the US Department of Energy, the National Science
Foundation, the North Atlantic Treaty Organization (NATO) and
the UCI Council on Research, Computing and Library Resources.
|
