Sea air in coastal cities, renowned for being bracing and healthy, is instead being heavily polluted by dirty smoke from ships a study has found.
Scientists have found ships are contributing far more polluting tiny sulphur rich particles than had previously been thought.
quality in coastal cities the study found
The tiny particles travel large distances and can become lodged in the lungs, posing a serious health hazard.
Previous studies have shown ship smoke may be responsible for as many as 60,000 deaths worldwide, according to an earlier study conducted at the University of Delaware.
"This is the first study that shows the contribution of ships to fine particulates in the atmosphere," said Prof Mark Thiemens, who headed the research team at the University of California, San Diego.
"Ships are really unregulated when it comes to air pollution standards. 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."
Primary sulphate, or SO4, is produced when ships burn a cheap, sulphur-rich fuel called "bunker oil."
The scientists say, these primary sulphate particulates are particularly harmful because they are especially fine, less than 1.5 microns or millionth of a metre in size.
As a result, they can travel extremely long distances because they stay in the atmosphere for longer periods and, unlike bigger dust grains and particles that are removed by the body when breathed, remain in the lungs.
Using a chemical fingerprinting technique to sample 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 per cent of the sulphate found in fine particulate matter in the atmosphere of coastal California.
On the days when the proportion of ship sulphate approached one-half of the fine particulate matter, the scientists determined from wind direction and speed calculations that ships burning high sulphur fuel in the Los Angeles, Long Beach and San Diego ports were a major influence.
"Our results suggest that this component of ship emissions is important and should not be ignored in the future," said Dr Gerardo Dominguez, first author.
In another study in the same journal, a team warms that the future impact of global warming is even worse than predicted when the grazing animals are taken into account.
The impact of global warming in the Arctic was studied by Penn State biologists, Dr Eric Post and Christian Pederson, to show that grazing animals will play a key role in reducing the anticipated expansion of shrub growth, thus limiting their predicted and beneficial carbon-absorbing effect.
While Dr Post and Pederson agree that global warming will promote the growth of shrubs, they argue that grazing by muskoxen and caribou will reduce the carbon-mitigating benefit of the plants, based on the findings of a novel five-year experiment in West Greenland in which they compared the effects of grazing in plots treated with increased temperatures versus those left untreated.
"We need to be aware that the 'carbon dioxide sponge' - represented especially by shrubs and trees - may not be as big as we thought it was," said Dr Post. "This finding is yet another reason to think carefully about reducing carbon-dioxide emissions."