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Air Pollution On The Sea Breeze

Local council's around New Zealand are battling to reduce air pollution said to be caused from burning fossil fuels. But new California research suggests a previously unknown intense chemical reaction between sunlight, air and sea salt is a major contributor to air pollution. John Howard reports.

As an island nation sunshine and salty air are among the sought-after pleasures of our life-style. We also like driving our cars which produce toxic emissions.

A recent University of California Irvine Study says those components are a major contributing factor to air pollution.

"If we want to understand the climate, truly you have to understand the dynamics of sea salt," said Donald Dabdub, an assistant professor of mechanical and aerospace engineering who did the research along with chemistry professor Barbara Finlayson-Pitts.

Scientists now say their findings will have significant implications for addressing greenhouse gases and pollution in coastal areas, as well as understanding climate change, since salt water covers two-thirds of the Earth's surface.

The process the researchers studied started with particles of sodium chloride, or sea salt, and water in the air over the ocean and the coast. Offshore breezes push that ocean air inland.

They found that when sea salt is exposed to daylight, it undergoes a previously unrecognised reaction on the surface of the salt particle that eventually results in the release of chlorine gas.

This chlorine gas, coupled with the emissions from the burning of fossil fuels, increases the amount of ozone - the key constituent of smog - in the lower atmosphere.

Previously, scientists had thought the chemical reaction occured inside the salt particle and therefore did not release chlorine gas.

"The chemistry was basically a reaction on the surface of the particle and we were able to show that this interface has a key role that orchestrates the reaction in such a way that we are now able to explain all sorts of things that were misunderstood about chlorine chemistry," Dabdub said.

"The plot thickens when all these chlorine gases are in the presence of products of combustion," he added.

Though ozone in the stratosphere is beneficial because it blocks the sun's ultravoilet rays, ozone in the lower atmosphere is an irritant to lungs and eyes.

Christchurch and Auckland, for example, are on the coast, have high ozone levels which produces smog problems and Christchurch plans to ban coal burning by 2003. The geography of Christchurch also plays a significant role. By comparison Auckland has high vehicle useage.

Wellington doesn't have the air pollution problem of the other two because it has higher winds to blow the smog away.

This new research reveals that previously unknown chemical reactions in sea salt coupled with the emissions and geography are what is causing the air pollution.

Smog is a brew including chemicals, solvents, emissions and exhausts - and now chlorine from sea salt.

For those Scoop scientific buffs the University of California researchers found;-

sunlight breaks apart ozone molecule (O3) - one of the resulting oxygen molecules (O) attracts a hydrogen molecule (H) from water in sea salt (H2O and NaCl)

The resulting hydroxyl radical (OH) adheres to and reacts with chloride (Cl) on surface of sea salt, eventually producing chlorine (Cl2) gas, which, when combined with emissions from burned fuel, produces more ozone.


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