updated 7/9/2008 6:00:44 PM ET 2008-07-09T22:00:44

Ah! The cold splash of the ocean, the sooty smell of the sea.

Sooty?

That's right, according to a new study of commercial vessel emissions, large cargo ships spew more than twice as much soot as previously estimated.

And worse, for folks who live in port cities, tugboats are the sootiest of all.

Overall, commercial ships release some 130,000 metric tons of soot per year, or 1.7 percent of the global total — much of it near highly populated coastlines, researchers report in Friday's edition of Geophysical Research Letters.

And global shipping is expected to grow 2 percent to 6 percent annually in coming years, according to the research team led by Daniel Lack of the National Oceanic and Atmospheric Administration.

The small dark soot particles absorb sunlight, the researchers pointed out. The particles create haze and affect how clouds form and make rain, changing a region's heat balance, according to the study.

In addition, the researchers warned, if commercial shipping expands into Arctic waters as ice cover lessens, soot will become a growing problem there too.

"Commercial shipping emissions have been one of the least studied areas of all combustion emissions," Lack said in a statement.

Previous studies had focused on only a few ships. His team examined 96 vessels along the U.S. southeast coast and Texas during the summer of 2006.

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