Sulfur emissions are an ingredient in acid rain. The study also said that ships pump out 14 percent of the world's nitrogen oxide emissions. Put another way, that's equal to the nitrogen emissions from all the cars, trucks and other vehicles in the United States. Nitrogen oxide can form ozone, an irritating substance in smog. Nearly 95 percent of the world's large vessels have diesel engines.
Bunkers are fuels leftover from the refining process.
It's the fuel nobody wants. Nobody but ship owners. But it's a dirty fuel. In the past, scientists and regulators looking for air pollution culprits have focused on factories, power plants and cars. Last September, the International Maritime Organization, a branch of the United Nations, tried to put a lid on ship exhaust, adopting measures that require ships to burn cleaner fuels.