The California Air Resources Board, or ARB, said in a written statement that the new regulation would eliminate an estimated 15 tons of exhaust a day from ships calling on the state's busy seaports.

The aim is to reduce emissions of sulfur and nitrogen oxides as well as particulate matter in the air.

"This regulation will save lives," said ARB Chairwoman Mary Nichols. "At ports and all along the California coast we will see cleaner air and better health."

The regulation, which takes effect next year, bans ships from burning heavy bunker oil in their engines within 24 miles of the California coast. Vessels will have to switch to low-sulfur marine diesel.

The rule, which applies to U.S. and foreign-flagged ships, will be implemented in two phases between 2009 and 2012 and will result in reductions of 83 percent for particulate matter, 95 percent for sulfur oxides and 6 percent for nitrogen oxides.