Oregon Public Broadcasting

168 countries, including the U.S., have signed onto an international treaty controlling air pollution by ocean-going ships. Christy George reports.

300,000 ships are at sea, but when they come into port, their engines emit sulfur and particulates.

And the problem is expected to get much worse over the next 15 years.  That's because global trade is projected to increase by 70 percent.

Aaron Ellis of the American Association of Port Authorities used to work at the Port of Portland.

He says West Coast ports in Los Angeles, Long Beach and the Pacific Northwest led the way by voluntarily cutting emissions on the ground.

Aaron Ellis: "Portland has been a leader in this area, Seattle, Tacoma, Vancouver, Canada just recently won an AAPA award for their program on reducing air emissions, and it's something we see cascading around the country."

Ellis says container ships tend to have newer, cleaner engines.  But by 2012, ships that burn dirty bunker fuel will have to start retrofitting their engines, or capturing pollution before it hits the air.