Ship emissions: sizing up a big problem

Those who go down to the sea in ships – or go to see them in port – may soon be able to breathe easier. Scientists have made the first measurements of ship emissions involving particles less than a millionth of a meter in size. They say it’s an important step in establishing and monitoring the effectiveness of air-pollution regulations for ships.

Until now, researchers in port cities have had a hard time figuring out what proportion of fine sulfate particles come from ships burning high-sulfur bunker oil, compared to the diesel trucks or trains that serve the cities. These fine particles are less than 1-millionth of a meter across. Once inhaled, these particles stay put, researchers say, constituting a potential public-health hazard.

Scientists at the University of California at San Diego found that ships approaching or in port can account for almost half of the fine sulfate particles found over coastal southern California. No one expected ship emissions of these particles to be so high, according to Mark Thiemens, a UCSD biochemist who led the study. The team applied an approach that has been used to tease out sources for other chemicals in the atmosphere.

Combined with wind patterns, the team’s technique allowed it to trace the origin of plumes to locations as far away as the Port of Los Angeles. The technique holds the promise of helping local officials better understand sources of pollution undercutting air quality, the researchers say. In July 2009, California will require ships to shift from bunker fuel to cleaner fuels when they approach within 24 miles of the coast.

The results appear in this week’s issue of the Proceedings of the National Academy of Sciences.