Science Bit

Acid-catalyzed process helps multiply particulates

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 aldehydes—organic compounds emitted by vegetation and formed when fossil-fuel emissions are oxidized—the 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 UNC team.

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


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