PITTSBURGH--Air emissions from trade-carrying cargo ships powered by diesel engines are among the world's highest polluting combustion sources per ton of fuel consumed, according to Carnegie Mellon University researchers James Corbett and Paul Fischbeck in their Oct. 31 Science magazine article, "Emissions From Ships."
The authors, researchers in the Department of Engineering and Public Policy, assert that anthropogenic emissions from cargo ships provide an alternate explanation to an emissions pattern generally attributed to persistent continental pollution. The authors say that multinational policies to address the problem will be implemented soon by the International Maritime Organization (IMO), although new NOx regulations will apply only to new ships or major ship conversions on or after Jan. 1, 2000.
Based on calculations used to obtain a conservative figure on total emission from shipping, the authors' findings conclude that "worldwide ship nitrogen emissions are equal to nearly half of the total emissions from the United States, 42 percent of nitrogen emissions from North America, 74 percent of emissions from the Organization for Economic Cooperation and Development (OECD) Europe and 190 percent of those from Germany. They are equal to 100 percent of nitrogen emissions from U.S. mobile sources and 87 percent of nitrogen emissions from U.S. stationary sources."
They add that "ship sulfur emissions equal 43 percent of total sulfur emissions from the United States, 35 percent of sulfur emissions from North America, 53 percent of emissions from OECD Europe and 178 percent of those from Germany. Most of the continental sulfur emissions are from stationary sources."
According to Bryan Wood-Thomas, Marine Policy Advisor, Office of International Activities, U.S. Environmental Protection Agency (EPA), "the research and analysis undertaken by Corbett and Fischbeck represents the most thorough examination of sulphur oxide and nitrogren oxide emissions associated with international shipping. While some studies have modeled emissions at the local and regional level, this study represents a rigorous analysis and estimation of emissions on a global scale."
Taking into account ship nitrogen and sulfur emissions, the authors estimate that these emissions affect global background pollution levels. Air over the North Pacific is more polluted than air over the South Pacific, and ship traffic is more concentrated in these areas studied.
The authors assert that the concentration of contaminants such as sulfur, ash asphaltenes and metals in the residuals (or marine fuels) has increased over the decades, especially since the 1973 fuel crisis when residual fuels were starting to be made using secondary refining technologies to extract the maximum quantity of refined products (distillates) from crude oil. Other ship fuels are distillate oils of higher grade; however, these are often blended with residuals. Seventy to 80 percent of commercial shippers prefer to use the cheaper residual fuels.
Data from three well-regarded industry sources were used to assess global ship emissions: marine exhaust emission test data that report fuel-based emission rates for sulfur and nitrogen, international marine fuel usage information, and the engine characteristics of the world's registered commercial ships weighing 100 gross registered metric tons or more and those of naval ships.
Although global emission limits were approved by the IMO diplomatic session in September and this will eventually result in multinational consensus on the principles of ship emission control, the authors report that "a measurable reduction in nitrogen emissions will not occur for many years," based on a 1.5 percent yearly fleet replacement rate. They assert that "for NOx controls that reduce emissions by 30 percent to 50 percent, IMO regulations would reduce emissions by less than one percent per year." Further, they add, "IMO language limits fuel-sulfur levels 4.5 percent. This provides little reduction, if any, and practically codifies the status quo, since the International Organization for Standardization (ISO) limited fuel to five percent sulfur in 1987."
Additional policy concerns cited by the authors include the IMO selection of the Baltic Sea as the first SOx Emission Control Area, which represents a relatively small percent of annual ship sulfur emissions within potential transport distance to land; the registration of ships by many nations, resulting in a difference between the country in which the ship is owned and the country in which it is registered, thereby limiting policy enforcement; and open-market interests and treaty commitments affecting the flow of trade.
Air emissions such as these may play a role in global climate change. Research in this area is continuing at the Center for Integrated Study of the Human Dimensions of Global Change at Carnegie Mellon, with funding from the National Science Foundation (grant SBR9521914) and academic funds from the university.