Large riverside cities like Portland, St. Louis, Nashville and New Orleans should look beyond road traffic to an important but usually overlooked source of air pollution — river traffic.
Commercial marine traffic on rivers emits substantial pollution, according to a study reported in the March 15 issue of Environmental Science and Technology, a peer-reviewed publication of the American Chemical Society, the world’s largest scientific society. The pollutants include nitrogen oxides, fine particulate matter and sulfur oxides.
Around riverside cities, nitrogen oxide pollution from shipping can equal that from a major freeway full of traffic, according to James J. Corbett, Ph.D., an assistant professor at the University of Delaware's College of Marine Studies, Newark, who conducted the study.
Corbett’s findings are based on a detailed inventory of air emissions from commercial vessels — such as ships, tugs and towboats — in the Northwest United States. The results suggest the importance of boat and ship emissions in many regions of the country, he says.
The inventory is the first to detail the type of geographically detailed estimates that modelers need to determine how boat and ship emissions affect regional air quality, according to Corbett.
Corbett, a former U.S. Merchant Marine engineering officer, combined analyses of engine operations with trade data about the tons of cargo and vessel movements over specific segments of the major rivers in the Pacific Northwest to come up with his estimates.
The study was commissioned to find out if ship and boat emissions contribute to haze that occurs in the federally designated Columbia River Gorge National Scenic Area in Washington and Oregon states, says Michael Boyer, an environmental scientist with the Washington Department of Ecology in Olympia, Wash., which helped fund the study.
“In the past all we had were rough estimates of marine vessel emissions and we couldn’t specify where the pollution occurred,” Boyer says. “This study means that we will be able to pin down the effects of ship emissions.”
Two years ago, Corbett inventoried national emissions from commercial waterborne vessels and found emissions were double previous estimates. His research showed that, as a source of nitrogen oxides for the entire country, unregulated waterborne commerce ranks higher than many regulated industries, including metals processing, petroleum industries and chemical manufacturing.
Waterborne commerce transportation is an essential element of the U.S. transportation infrastructure that often seems invisible to the U.S. public, according to Corbett. Ships and boats that carry very large loads for very long distances move between 22 percent and 24 percent of U.S cargo, measured in ton miles — comparable to truck transportation, which accounts for 25 percent to 29 percent, he said. Waterborne transportation can also be one of the most energy-efficient ways to move cargo, using about one-tenth of the energy consumed by the U.S. trucking industry, Corbett added.
Materials provided by American Chemical Society. Note: Content may be edited for style and length.
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