Sea spray rinses out air pollution

WASHINGTON -- That salty spray from the ocean gives the air more than a refreshing tang. It appears to provide a scrubbing, too.

A team of Israeli researchers reports that, by encouraging increased rainfall, the sea spray helps wash pollution from the air.

"The conclusion stands that the air that we breathe near the surface remains clean because of the fact that the oceans are salty," said Daniel Rosenfeld of Hebrew University in Jerusalem.

"We have discovered a process by which nature apparently cleanses the ... air pollution quite effectively when it spills from land over to the oceans," he said.

Practically all the pollutants are removed at the lower layer of the atmosphere, Rosenfeld said. That is one reason why the air in Hawaii is always so pristine, except during volcanic eruptions, he said.

Rosenfeld and his colleagues used satellite data to study the air over the Indian Ocean, where massive amounts of particles from burning, urban air pollution and desert dust are blown from southern Asia.

But such effects "are not unique," he said.

Nearly three-fourths of the Earth's surface is covered by water and the winds are constantly moving air from land onto the oceans and from the oceans onto land worldwide.

Rosenfeld's findings were reported in the journal Science.

"The paper presents an interesting point, which has not been discussed for some time," said John N. Porter of the Hawaii Institute for Geophysics and Planetology.

Porter said the idea of sea salt initiating rainfall was proposed in the 1950s, but studies in the 1970s seemed to show it was not an important factor. Rosenfeld's work appears to support the earlier research, he said.

Porter, who was not on Rosenfeld's team, said his own research indicated salt helped to increase rainfall in relatively clean air but was less effective in more polluted conditions.