Tugboats puff out more soot for the amount of fuel used than other commercial vessels, and large cargo ships emit more than twice as much soot as previously estimated, according to the first extensive study of commercial vessel soot emissions. Scientists from NOAA and the University of Colorado conducted the study and present their findings in the July 11 issue of the journal Geophysical Research Letters.
The primary sources of soot, or small particles of black carbon, are fossil fuel combustion, wildfires, and burning vegetation for agricultural purposes. In the Arctic, an increase in soot may contribute to climate change if shipping routes expand, according to the study.
"Commercial shipping emissions have been one of the least studied areas of all combustion emissions," said lead author Daniel Lack, of NOAA's Earth System Research Laboratory (ESRL) 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 the summer of 2006. From the NOAA research vessel, Ronald H. Brown, the team measured black carbon emitted by tankers, cargo and container ships, large fishing boats, tug boats, and ferries, many of them in the Houston Ship Channel.
Commercial shipping releases roughly 130,000 metric tons of soot per year, or 1.7 percent of the global totalmuch of it near highly populated coastlines, the authors estimate. In the coming years global shipping is expected to grow two to six percent annually.
Tugs emit nearly a gram of soot per kilogram of fuel burnedtwice as much as any other vessel type, the authors found. The high levels point to their low-quality fuela thick, black tar left over from crude oil af