Commercial Ships' Soot Emissions Much Higher Than Expected

The first extensive study of commercial vessels' emissions of soot found that large cargo ships emit more than twice as much as previously estimated, scientists from NOAA and the University of Colorado report in the July 11 issue of the journal Geophysical Research Letters. Tugboats emit more soot for the amount of fuel they use than do other commercial vessels, the researchers found.

Lead author Daniel Lack observed soot emissions from 96 commercial vessels from a NOAA research ship. NOAA says the chief sources of soot (small particles of black carbon) are fossil fuel combustion, wildfires, and burning vegetation for agricultural purposes. In the Arctic, an increase in soot could contribute to climate change if shipping routes expand as expected, the study concluded.

"Commercial shipping emissions have been one of the least-studied areas of all combustion emissions," said Lack, who works for NOAA's Earth System Research Laboratory and the NOAA-CU Cooperative Institute for Research in Environmental Sciences. "The two previous studies of soot emissions examined a total of three ships. We reviewed plumes from 96 different vessels." Lack and his colleagues observed emission plumes from commercial vessels in open ocean waters, channels, and ports along the southeast United States and Texas during summer 2006. The observed vessels included tankers, cargo and container ships, large fishing boats, tugboats, and ferries, many of which were in the Houston Ship Channel when observed.

The authors estimate commercial shipping releases about 130,000 metric tons of soot per year, or 1.7 percent of the global total, with much of it emitted near highly populated coastlines. "Tugboats are a huge source of black carbon that may be under-reported or not reported at all in emissions inventories compiled by ports," Lack said in a news release posted by NOAA.

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