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Summer 2000

Science Bits

Airborne sea salt particles may influence air pollution levels

Barbara Finlayson-Pitts and Donald Dabdub (University of California, Irvine), working with other molecular researchers, have shown 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.

In sunlight, chlorine 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. 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."

The researchers observed the reaction of hydroxyl radicals with particles composed of water and sodium chloride—the basis of sea salts. They found unique chemical reactions on the surface of the sea salt particles rather than inside the particles, as had been previously observed. Their discovery suggests that the creation of atmospheric chlorine through sea salt interaction may be greater than previously realized.

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 conditions was observed in this study.

In continuing this research, Dabdub will introduce this information on sea salt chlorine creation into a computer model 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, Matthew Lakin, Krishna Foster, R. Benny Gerber, and Douglas Tobias of UCI and Pavel Jungwirth of the J. Heyrovsky Institute of Physical Chemistry in the Czech Republic. The findings were published in Science. The study was funded by the U.S. Department of Energy, NSF, the North Atlantic Treaty Organization, and the University of California, Irvine, Council on Research, Computing, and Library Resources.

University of California, Irvine

Ice-age El Niño teleconnection discovered in New England

Doctoral candidate Tammy Rittenour (University of Nebraska–Lincoln), Julie Brigham-Grette (University of Massachusetts), and Michael Mann (University of Virginia) have found evidence of El Niño effects in New England's climate 17,500 to 13,500 years ago during the late Pleistocene era.

According to Rittenour, "There was no evidence prior to this research that [El Niños] occurred during glacial time periods. For them to be seen in North America, let alone right at the toe of the last ice sheet, is unexpected." The discovery was announced in Science.

Rittenour made the discovery while looking for evidence of how glacial Lake Hitchcock drained at the end of the last ice age. The lake extended from what is now southern Connecticut to northern Vermont. Rittenour's team used well-drilling equipment at the University of Massachusetts campus in Amherst to pull cores from the ancient lake bed that totaled 110 feet.

Each year of sediment consisted of two layers, a light-colored one composed of heavy summer silt and a darker one from winter. Rittenour counted 1,389 varves, or years' worth, of sedimentation and determined their approximate age by radiocarbon dating. She noticed that there was a variance in the thickness of the layers and thought it might be climate related. After correlating her specimen with the 4,000-year varve chronology of Ernst Antevs, she and her colleagues performed a statistical analysis to look for climate signals and a spectral analysis to look for periodicities. They found a grouping of three peaks of varve thickness: one between 2.5 and 2.8 years, one between 3.3 and 3.5 years, and another from 4 to 5 years"

"This is right in the modern El Niño climate frequency," Rittenour said. "The fact that there are three peaks is related to the way El Niño operates, and this gives us a better idea that this is El Niño. We expected some climate signals were recorded in the sediments because of how the thickness of the lake sediments change from year to year. But we expected the climate to be influenced by the North Atlantic Oscillation, which is closer to New England, and not a climate signal from the tropical Pacific."

The project was funded by NSF, the National Geographic Society, and the University of Massachusetts.

University of Nebraska–Lincoln, University of Massachusetts, University of Virginia

Winds in Pacific climate cycle can foretell Gulf of Mexico hurricanes

The Madden-Julian Oscillation (MJO), which builds in the Indian Ocean and moves eastward through the equatorial Pacific Ocean, is a key factor in the formation of hurricanes and tropical storms over the Gulf of Mexico and the western Caribbean Sea, according to Eric Maloney and Dennis Hartmann (University of Washington). Their work was reported in Science.

The MJO is associated with westerly winds in the Pacific. Data culled from climate and weather records from 1949 through 1997 show that, about 15 days after detection of those winds in the western Pacific, hurricanes and tropical storms are four times more likely to form in the gulf and in the western Caribbean, the scientists said. The area extends from eastern Texas to about the eastern edge of Cuba, and Florida appears to be very vulenrable to such storms.

Having advance knowledge that conditions will be favorable for hurricanes to form might give officials and residents of the Gulf Coast and Caribbean islands more time to prepare, and also could prove valuable to shipping interests, Hartmann said. However, "You can say maybe a week in advance that there are likely to be hurricanes in the Gulf of Mexico, but I can't tell you whether they're likely to hit New Orleans or Galveston."

The Madden-Julian Oscillation repeats every 30 to 60 days. It rises in the Indian Ocean and stays close to the equator as it moves across the Pacific. The leading area of the system typically carries the easterly winds that are predominant in the tropics. The center of the system often contains storm activity, and the westernmost section carries the telltale westerly winds.

Maloney and Hartmann examined wind speeds at an altitude of about 4,500

feet, using data for June through November—the Atlantic hurricane season—over 48 years. They found that when easterlies averaging 7 or 8 miles per hour were replaced by westerlies of the same strength, the difference of 15 mph or more correlated strongly with increased hurricane formation in the gulf and the western Caribbean. In addition, there are indications that the storms generated are more powerful if the westerlies in the Pacific are stronger.

University of Washington

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