Waterways pollute air

Ships and boats could be polluting the air as much as do cars and lorries. A new study from the US Pacific Northwest1 suggests that waterways should be included in air-pollution audits that have so far focused on industry and road traffic.

"If a single freeway needs to be included in modeling of emissions impacts, then the waterway most certainly should be," says the study's author Jim Corbett, a marine policy researcher at the University of Delaware.

Corbett has found that marine vessels emit twice as much nitrogen oxides (NOx) - up to 25% of Washington statès highway emissions -as had previously been estimated. NOx are highly reactive gases implicated in a variety of environmental ills, including global warming, acid rain and smog.

"For the most part, these marine traffic emissions have been missing," agrees Brian Lamb, who models air quality at Washington State University in Seattle. Previously, emissions were assessed from ships in port - only about 10% of the total from US waters.

Decreases in industry emissions over the past 30 years have enabled researchers to identify other important sources of air pollution. Three years ago Corbett showed that previously-ignored ships contribute enough sulphur dioxides to the oceans' atmosphere to impact on global climate2.

Now he has refined his projections to regional levels - combining analyses of fuel consumption, traffic movements and cargo loads on smaller river systems.

Hazy figures

Thousands of boat trips on the Columbia and Snake river systems each year transport wheat, forest products and fertilizers throughout the inland Northwest. As diesel burns, it emits NOx and other haze-causing pollutants, such as particulates and sulphur dioxide. These scatter light, lower visibility and contribute to respiratory illnesses.

Hazy days are of increasing concern to regional environmental planners. Amendments to the Clean Air Act in 1990 and current Environmental Protection Agency efforts specifically call for lowered haze in environmentally protected areas, such as the Columbia River Gorge National Scenic Area.

Emissions from sources other than road traffic are difficult to gauge. So standards for these have lagged behind the strict regulations for cars and vans that plan to bring road-vehicle emissions down 70% over the next 20 years.

Corbett's work suggests that similar restrictions should apply to waterway traffic. Otherwise "nonroad sources may produce more than onroad sources, at some point," says Mike Boyer, environmental scientist with the Washington Department of Ecology in Olympia, Washington.
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References

1. Corbett, K Emissions from ships in the northwestern United States. Environmental Science and Technology, 36, 1299 - 1306, (2002).
2. Capaldo, J.J., Corbett, K, Kasibhatla, P., Fischbeck, P. & Pandis, S.N. Effects of ship emissions on sulphur cycling and radiative climate forcing over the ocean. Nature, 400, 743 - 746, (2002).