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Sulfur Skies
August 18, 1999
image: U.S. Army Corps of Engineers

Professor Spyros Pandis of Carnegie Mellon University reports in the current issue of the British journal Nature that emissions from ship engines may be a major cause of sulfur dioxide concentrations in the skies over much of the Earth’s coastal regions and oceans.

High concentrations of sulfur in what are otherwise remote, pristine areas had baffled scientists for years. Although algae release sulfur when they die, it is not enough to explain white streaks above international shipping lanes spotted by satellites in space. The white streaks represent highly reflective clouds that appear brighter because they are reflecting solar light back out into space.

image: NASA

What makes them so reflective? The sulfur spewing from ship smokestacks, Pandis says.

"Ships, through their smokestacks, emit sulfur gases," Pandis says. "These gases are reacting in the atmosphere and form particles. So when we make more sulfur, we form more particles. These particles go through the clouds and become cloud droplets. So more pollution means more cloud droplets and when a cloud has more droplets it is brighter, and reflects the radiation back from space."

Filthy Fuel

image: Spiros Pandis

Ships burn some of the cheapest, dirtiest fuel available. It contains 1,000 times more sulfur than ordinary gasoline.

"The fuel used by these boats is called marine fuel and it is actually the bottom of the barrel in the petroleum processing," Pandis says. "After all of the high quality fuels like gasoline have been taken out, whatever’s left is ... the one used by boats. It’s black, extremely thick and smells awful."

According to a study conducted by the Universities of Nevada and Washington, a large freighter emits more sulfur than a small city.

Good Pollution?

The net result of the sulfur-saturated clouds is actually global cooling because they reflect some of the sun’s heat back into space. That’s something which might appear to come in handy as the planet slowly heats up from global warming. So should ships pollute even more? Absolutely not, says Robert Charlson of the University of Washington in Seattle. "There is no possibility of a global compensation. Global warming is accumulative, this [phenomenon] is not."

And the sulfur has many other dangerous "side-effects" that cancel any tiny benefit coming from global cooling. When ships are within several hundred miles of land, the sulfur often washes up ashore in the form of toxic acid rain which poisons the environment.

Professor Pandis relates some other health hazards: "The particulate matter are known to be a health hazard in polluted areas like Los Angeles.They do contribute to people getting sick and even dying in extreme cases. Even in areas a lot cleaner than Los Angeles, these particles create haze; they reduce the visibility and the quality of life."

A Solution to the Pollution?

image: University Consortium of Atmospheric Research

Professor Pandis notes that the problem of ship emissions is huge. "Our estimate is that there are approximately 100,000 ships around which emit or actually consume 150 million tons of fuel per year. If we want to reduce their emission we need to either use cleaner fuel…or we need to install different cleaning methods on the boats to remove the pollutants before they are emitted." But both methods are expensive and will increase the cost of maritime shipping, Professor Pandis notes.

International law is attempting to address the problem, but it hasn’t had much of an impact yet, Pandis says. A treaty drafted by the the International Maritime Organization limits sulfur emissions to 4.5-percent, but most ships already use fuel with 3-percent sulfur content.

And international shipping treaties are inherently difficult to enforce, Pandis says. "The boats are owned by one country, but often fly under the flag of another and they travel between other countries. It’s a complex political problem."

NASA is planning a special satellite mission in 2003 called Picasso-Cena which will further study the effects of sulfur emissions on Earth’s atmosphere.

That’s a far cry from several decades ago when Pandis first began pondering the effects of ship pollution from the Greek island of Poros. "I grew up on a small Greek island, and the one thing you could notice was that every time a big boat or a cruise ship would pass by there would be a dark plume following it. There was always the question, how much they are polluting the environment, somewhere in the back of my mind. Ships are a much more important contributor to atmospheric pollution that anybody thought until now."

Elsewhere on the Web

International Maritime Organization

School of Ocean and Earth Science and Technology, University of Hawaii

"Cost-effectiveness of controls on sulphur emissions from ships" -- Article from Concawe Review, publication of CONCAWE, the European oil companies’ organization for environment, health and safety.

by STN2

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