"California this week put in place the toughest restrictions in the world on smog from ships, requiring reductions of more than 80 percent of soot from foreign and US ships out to 24 miles from shore. Tankers, cargo vessels and cruise ships burn bunker fuel, which has sulfur content as much as 1,000 times higher than on-road diesel. The US is moving forward to copy California's rules by 2015."
California Imposes World's Toughest Smog Rules for Ships
Source: San Jose Mercury News, 07/06/2009