Slowing cargo vessels near coastlines by 10 to 15 miles per hour could dramatically cut ships’ air pollution, according to a new study. But only a few U.S. ports have initiated such efforts. A speed limit of 14 mph, down from the current cruising speeds of 25 to 29 mph, would cut nitrogen oxides – a main ingredient of smog – by 55 percent and soot by almost 70 percent. It also would reduce carbon dioxide – a potent greenhouse gas and key contributor to climate change – by 60 percent. With 100,000 ships carrying 90 percent of the world’s cargo, air pollution is a heavy burden for people living near ports, so slowing ships could improve their health, researchers say.