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Chemists at the University of California, San Diego have measured for the first time the impact that dirty smoke from ships at sea and generating electricity in port can have on the air quality of coastal cities.

The scientists reported the findings this week in the online edition of Proceedings of the National Academy of Sciences, an academic journal. Basically, the impact of dirty smoke from ships burning high-sulfur fuel can be substantial, on some days accounting for nearly one-half of the fine, sulfur-rich particulate matter in the air known to be hazardous to human health.

Sampling air at the end of the pier at the Scripps Institution of Oceanography in La Jolla, the scientists found that the smoke from ships contributed as much as 44 percent of the sulfate found in fine particulate matter in the atmosphere of coastal California. On the days when the proportion of ship sulfate approached one-half of the fine particulate matter in the air, the scientists determined from wind direction and speed calculations that ships burning high-sulfur fuel in the Los Angeles, Long Beach and San Diego ports were a major influence.

Sulfate particulates are particularly harmful to humans because they are especially fine microscopic particles, less than a millionth of a meter. That makes them able to travel extremely long distances and, unlike bigger dust grains and particles that are removed by the body if breathed in, the tiny particles can remain in the lungs.

The Port of Los Angeles, for example, can have a significant influence on air quality in San Diego because the particles travel so far, the study said.

Chemists developed a chemical fingerprinting technique that allowed the scientists to distinguish primary sulfate from ship smoke from the tailpipe emissions of trucks, cars and other sources. The researchers discovered that primary sulfates from ship engines incorporate molecular oxygen — the type we breathe in — and are easily distinguished from primary sulfates from car and truck diesel emissions.

The results have particular significance for the state which beginning next year will require that all tankers, cargo and cruise ships sailing into a California port switch to more expensive, cleaner-burning fuels when they come within 24 miles of the coast.

Similar international rules requiring clean-burning ship fuels are set to take effect in 2015.

The researchers said the chemical fingerprinting technique they developed could assist the California Air Resources Board, as well as regulators in other states and countries, monitor the impacts of ships off their coasts as new restrictions on bunker oil burning by ships are implemented.

DARRYN BENNETT

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