Ship sulfur emissions found to strongly impact worldwide ocean and coastal pollution

August 19, 1999

PITTSBURGH -- Ship emissions are a dominant contributor to atmospheric sulfur dioxide concentrations over much of the world's oceans and in several coastal regions, researchers from Carnegie Mellon University and Duke University report in a Nature article today.

This news follows the Carnegie Mellon team's initial finding that air emissions from trade-carrying cargo ships powered by diesel engines are among the world's highest polluting combustion sources per ton of fuel consumed, published Oct. 30, 1997 in Science.

The most important finding from this study, according to Carnegie Mellon authors Spyros Pandis, James Corbett, Paul Fischbeck and Kevin Capaldo, and Duke author Prasad Kasibhatla, is that ships affect scientific understanding of climate change.

Ships use the tar-like, sulfur-concentrated remains of petroleum left once the gasoline, oil and all other products have been extracted. This high-sulfur fuel is responsible for the significant environmental impacts of ship sulfur emissions. Regionally, sulfur emissions contribute to acid rain, which can pollute freshwater lakes and rivers, and damage vegetation.

"Ships also have been known to contribute to the formation of clouds over the ocean," Pandis said. "Sulfur emissions have a large role in the formation of aerosols (tiny particles) on which water condenses to form clouds. The interactions of aerosols and clouds have been identified as one of the most important uncertainties in understanding the rate of climate change, or global warming, because clouds reflect energy and thereby reduce the net warming effect of long-lived greenhouse gases."

"Since aerosols have a much shorter lifetime in the atmosphere -- about a week compared to decades and hundreds of years for greenhouse gases -- these effects have been difficult to quantify," Corbett added. "Our study shows that sulfur from ships may be an important factor in solving this part of the global climate change puzzle."

The study also shows that the effect of ship emissions is most evident in the Northern Hemisphere oceans, where greater than 60 percent of sulfur dioxide concentration in the atmosphere and 30 percent of all sulfates can be attributed to ships. Except for the area encompassing Australia, the Southern Hemisphere oceans are almost unaffected. This is because of the heavier shipping that occurs in the north. This is most important for coastal cities that receive the brunt of sulfur pollution from ships.

This study was funded by a grant from the National Science Foundation and the Department of Engineering and Public Policy at Carnegie Mellon.
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Carnegie Mellon University

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