New research says the impact of shipping on air quality in coastal areas could be worse than previously thought, with the finger of blame pointing to the use of high sulphur bunker fuels.

Researchers at the University of California at San Diego (UCSD) have used a chemical fingerprinting technique to identify "primary sulphate" in ship emissions consisting of tiny sulphur particles less than 1.5 microns across. 

These tiny particles, which can be carried long distances on the wind, are said to be particularly harmful to human health.  

"This is the first study that shows the contribution of ships to fine particulates in the atmosphere," said Professor Mark Thiemens, who led the scientific research which was published in the journal Proceedings of the National Academy of Sciences.

"What we wanted to find out was the contribution of ships to the air pollution in San Diego.  And what we found was a surprise, because no one expected that the contribution from ships of solid sulphur-rich particles, called primary sulphate, would be so high," Thiemens said.

Their analysis, which distinguished sulphur particles in ship emissions from the tailpipe emissions of trucks, cars and other sources,  found that ships contributed 44% of the tiny primary sulphate particulates polluting coastal California.

An earlier study, published in November 2007, estimated that emissions from ocean-going ships are responsible for 60,000 premature deaths a year.

In February 2008, Friends of the Earth International (FOEI) submitted further studies to the International Maritime Organization (IMO) saying the death-toll could rise to over 80,000 by 2012 unless cleaner fuel standards were ushered in.

"Ships are really unregulated when it comes to air pollution standards," UCSD professor Thiemens observed.

The shipping community may have a different view, with both the IMO and regional regulators addressing sulphur content in bunker fuel.

The California Air Resources Board (ARB) has approved new regulations which will require ships sailing within 24 nautical miles of California's coast to burn only distillate fuels with a lower sulphur content than normal bunker fuel already from July 1, 2009.

The IMO is due to give formal approval revised regulations dealing with air pollution from ships; MARPOL Annex VI, in October this year.

Under MARPOL Annex VI, vessels operating in designated emission control areas (ECAs) currently have to observe a 1.50% fuel sulphur limit.  The ECA sulphur limit will drop to 1.00% from March 2010 and again to 0.10% in January 2015.

Globally, the current bunker fuel sulphur limit of 4.50% will be reduced to 3.50% in January 2012, with a long-term global target of just 0.50% in 2020, subject to a review in 2018.

Most oceangoing ships today operate their main engines on high sulphur bunker fuels. 

Although the global limit is 4.50% sulphur, the average sulphur content of residual fuel oil used by ships decreased by 0.17% from 2.59% in 2006 to 2.42% in 2007, according to data compiled for the IMO.

Low sulphur fuels, in particular distillates, cost more than high sulphur bunker fuels, which means ships will face substantially higher fuel costs as stricter sulphur limits are imposed in the coming years.