Ocean air helps clean air pollution – UPI.com
JERUSALEM, Aug. 15 (UPI) — The oceans help banish air pollution, cleansing any dirty clouds above them with a breath of salt spray, new research from Israel suggests.
The way heavy air pollution appears to wash away relatively quickly when it mixes with clouds above the seas could help scientists devise new ways to purify the air over land as well, researchers said.
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“We can imitate artificially over land what nature does over the ocean, by cloud-seeding with salt spray,” researcher Daniel Rosenfeld, a cloud physicist at Hebrew University of Jerusalem, told United Press International. “We have started such an experiment in Israel for the purpose of rain enhancement, with preliminary encouraging results.”
Although the findings are somewhat relieving, Rosenfeld said, he does not recommend relying on the oceans to clean up after humanity’s mess — because the air pollution returns to Earth as acid rain. Also, although the air above islands such as Hawaii remains clear, the mainland atmosphere will remain as dirty as ever.
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“Air pollution will eventually start to decrease with the oceans’ help, but it will get a lot worse before it will start to get better,” Rosenfeld said.
Atmospheric pollution from fires, deserts and cities is made up of tiny particles each a thousandth the diameter of a human hair. When these dirty specks glom onto water in clouds, the resulting droplets are not large enough to fall as rain and instead result in a fine mist. Prior studies have shown this phenomenon results in suppressed rainfall over land.
“Without a lot of precipitation, you can’t wash away the pollution from the atmosphere,” Rosenfeld explained. That means air pollution remains trapped above land, at least until the clouds grow so big — 3.7 miles high — that they finally burst into storms.
Rosenfeld and his team found over the seas, dirty clouds have no problems shedding rain. “Sea salt aerosols play a major role in this difference,” he explained. It appears large particles of sea salt in ocean air attract the smaller water droplets that form around air pollution particles.
“The salty oceans can serve as very effective ‘green’ lungs for cleansing almost any amount of air pollution that we can put in the atmosphere in the foreseeable future,” Rosenfeld said.
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When researchers looked at the flow of cool and highly polluted air coming from winter monsoons off southeast Asia to the relatively warm waters of the Indian Ocean, they noticed the clouds generated rainfall when only about 1.3 miles high.
“Nature gives us humans — the polluters — a break. It cleans the air once it is over the ocean,” Yoram Kaufman, a senior atmospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., told UPI. Although Kaufman said he found the results “exciting,” he emphasized the study “has to be repeated on a larger scale” to see if this phenomenon truly has a larger, global impact.
The researchers said they currently are experimenting with cloud-seeding techniques from planes by spraying clouds above Israel with highly concentrated brine from the nearby Dead Sea. So far they have detected larger water droplets inside the clouds, but “there is still a very long way to go to operational seeding,” Rosenfeld said.
The research is reported in the Aug. 15 online version of the journal Science.
(Reported by Charles Choi, UPI Science News, in New York)
