This article is reproduced with the permission of New Scientist for exclusive use by Nova users.

Ozone smog spoils bracing seaside air
15 April 2008
From New Scientist Print Edition.
Kate Ravilious

If you do like to be beside the seaside, it might be best to avoid beaches near major ports. The mix of sea salt, ship fumes and city smoke leads to a chemical reaction that encourages the formation of ozone smog, adding to the pollution that forms in cities.

James Roberts from the National Oceanic and Atmospheric Administration Earth System Research Laboratory in Boulder, Colorado, and his colleagues have developed a mass spectrometer that can detect nitryl chloride (NO₂Cl) - a chemical that aids the formation of ozone.

Nitryl chloride is created when nitrogen oxides, which are present in ship exhausts and city smoke, mix with chloride-containing aerosol particles, such as spray from the sea. Until recently there was no way of measuring nitryl chloride, so nobody knew how much was floating around.

Cruising along the southern coast of the US, Roberts's team recorded unexpectedly high levels of nitryl chloride near Houston and Miami (Nature Geoscience, DOI: 10.1038/ngeo177). "We saw nitryl chloride levels over a part per billion on several occasions, more than 20 times greater than previous estimates," says Roberts.

During the day, sunlight breaks down the nitryl chloride into nitrogen dioxide and highly reactive chlorine atoms, which are known to encourage ozone to form.

Ozone in the lower atmosphere is a major pollutant. It is a cause of respiratory problems and may increase mortality rates. The finding provides yet another mechanism for the rise in pollution around cities.

Roberts suggests that areas most at risk include southern California, the eastern seaboard of the US and large parts of southern Asia, but as yet it is hard to judge how widespread this form of pollution is.

"It is possible that the overall importance of nitryl chloride is limited to heavily polluted conditions relatively close to major nitrogen oxide sources such as those investigated in this study," says Bill Keene, an atmospheric scientist at the University of Virginia in Charlottesville.

"Such chemistry could occur in any urban coastal regions, potentially leading to a globally significant effect," says Lucy Carpenter, an atmospheric chemist at the University of York, UK.

Even if the problem is largely confined to industrial ports, that doesn't mean it should be ignored. "These results reinforce the need to control nitrogen oxide emissions," says Alex Pszenny from the University of New Hampshire in Durham.

From issue 2651 of New Scientist magazine, 15 April 2008, page 14

For the latest from New Scientiist visit www.newscientist.com