Ships emit sulfates − the same polluting particles associated with diesel-engine cars and trucks that prompted improvements in on-road vehicle fuel standards. Sulfate emissions from ships vary with the concentration of sulfur in ship fuel, the authors find. Globally, fuel sulfur content is capped under the International Convention for the Prevention of Pollution from Ships. As a result of the cap, some ships use "cleaner," low-sulfur fuels, while others continue to use the high-sulfur counterparts.
Yet, sulfates make up just under half of shipping's total particle emissions, according to the new study. The other half, composed by organic pollutants and sooty, black carbon, are not directly targeted by today's regulations.
A 2008 study by Lack's team focused exclusively on soot (http://www.agu.org/sci_soc/prrl/2008-23.html). Emissions of these non-sulfate particles, the earlier study found, depend on the operating speed of the engine and the amount of lubricating oil needed to deal with wear and tear from burning less-refined fuels. "Fortunately, engines burning 'cleaner,' low-sulfur fuels tend to require less complex lubricants. So the sulfur fuel regulations have the indirect effect of reducing the organic particles emitted," says Corbett.
One surprising result of burning low-sulfur fuels is that, although total particle emissions diminish, the time that particles spend in the air appears to increase. It's while they're airborne that particles pose a risk to human health and affect climate.
Lack and colleagues find that the organic and black carbon portion of ship exhaust is less likely to form cl
|Contact: Maria-Jose Vinas|
American Geophysical Union