You may think that a short stroll on the beach is good for health. But, not according to a study, which suggests that sea air could actually leave you breathing in noxious chemicals that damage lungs.

An international team has carried out the study and found that smoke from vessels at sea or in port is affecting the air quality of many coastal cities across the world, which in turn is harming the health of many beach walkers.

According to researchers, 'primary sulphate' in ship emissions, consisting of tiny sulphur particles less than 1.5 microns across, when breathed in, can harm the lungs posing a serious health hazard, the Daily Mail reported.

Primary sulphate, or S04, is produced when ships burn a cheap sulphur-rich fuel called 'bunker oil'. The particles are believed to be especially harmful to human health because of their small size.

'This is the first study that shows the contribution of ships to fine particulates in the atmosphere. Ships are really unregulated when it comes to air pollution standards. What we found was a surprise, because no one expected that contribution from ships of solid sulphur-rich particles called primary sulphate would be so high,' lead researcher Professor Mark Thiemens said.

In their study, Prof Thiemens of California University and colleagues analysed the contribution of ships to the air pollution in San Diego. Air samples showed 44 per cent of the sulphate polluting coastal California can be traced to ships.

Co-researcher Dr Gerardo Dominguez said the research clearly showed that the potential risk from ship emissions was important and should not be ignored in the future, mainly by regular beach walkers.

The study has been published in the Proceedings of the National Academy of Sciences journal.