Acid-catalyzed process helps
A mix of inorganic pollutants, such as sulfuric or nitric acid, with
organic compounds produced by vegetation or combustion can lead to vast
increases in the formation of secondary organic aerosols (SOAs), a new
study indicates. These SOAs are a major contributor to the fine particulate
matter that may affect health and reduce visibility in both rural and
urban settings. Myoseon Jang, Nadine Czoschke, Sangdon Lee, and Richard
Kamens, all of the University of North Carolina at Chapel Hill, released
their findings in the 25 October 2002 issue of Science.
This underappreciated reaction may generate 5 to 10 times more
aerosol in the atmosphere than we previously thought, says Kamens.
It appears to explain a number of different kinds of phenomena
that lead to aerosol formation.
The team introduced fine inert particles, known as seed aerosols,
in indoor reaction chambers and large outdoor smog chambers. Some of
the seed aerosols were coated with sulfuric acid at levels similar to
those found on tiny bits of diesel soot. When these seed aerosols were
mixed with various types of aldehydesorganic compounds emitted
by vegetation and formed when fossil-fuel emissions are oxidizedthe
rate of aerosol growth increased dramatically.
The results are consistent with data collected in the Smoky Mountains
by a team from Rutgers, the State University of New Jersey. This work
may also help explain bursts of aerosol production observed in the Houston
area. There, petrochemical plants emit large amounts of sulfur dioxide
as well as volatile organic compounds. After the sulfur dioxide is oxidized
to form sulfuric acid, it may work in concert with the organic compounds
to step up aerosol production in line with the process outlined by the
According to the authors, most SOA research has focused on organic
precursors, while studies of inorganic aerosols have often neglected
the organic aerosol fraction. If the heterogeneous chemistry involving
both components can be modeled, they write, the predicted SOA
formation will be much greater and could have a much larger impact on
climate forcing effects than we now predict. Their exploratory
studies were supported by NSF and the Environmental Protection Agency.
University of North Carolina