Marine plants source of aerosols

A new study places plankton, kelp and seaweed alongside cars, factories and planes as sources of aerosols that may affect Earth's climate.

Ocean plants were fingered by an international team of atmospheric scientists and marine biologists tracing the tiny particles that cool Earth by seeding clouds and scattering incoming radiation.

Investigators from Ireland, Finland, Germany and the United States found sunlight can convert organic iodine vapors emitted by the aquatic organisms into secondary aerosols in sea air. If the transformation occurs on a large scale, it could significantly influence climate, they report.

Marine aerosols and their cloud-forming component can regulate climate by reflecting the Sun's rays, they said.

Changes in the activities of marine biota can trigger a chain reaction altering emissions of iodine vapors, which in turn switches Earth's "heat-shield," said lead author Colin O'Dowd, professor of physics at the National University of Ireland in Galway.

"The discovery of a previously unrecognized source of aerosol particles is big news to atmospheric scientists," said Charles Kolb, president of Aerodyne Research, Inc., in Billerica. Mass., who analyzed the findings in an accompanying commentary.

"One reason for the interest in atmospheric aerosols is their effect on climate and on our understanding of climate change. In particular, uncertainties about the composition and distribution of fine aerosol particles, no more than a few micrometers in diameter, cause large uncertainties in predictions or global warming driven by the accumulation of greenhouse gases."

Depending on their makeup, aerosols can affect Earth's "radioactive" balance by absorbing incoming solar radiation and leading to cooling, or warming, scientists told United Press International.

In less direct fashion, the particles can stimulate cloud production by inducing droplet formation in a cooling air mass, they said.

"The smaller droplets produce brighter clouds, which might also be longer lived because they are less likely to precipitate as rainfall," Kolb said. "Indeed, certain observations indicate that aerosols from forest fires and urban pollution can suppress rain and snow fall."

The work builds on previous field measurements along the coast of Ireland that pointed to a source of new marine aerosols not accounted for by known mechanisms or models.

In the new study, O'Dowd and his colleagues reproduced coastal conditions in a state-of-the-art atmospheric smog chamber at the California Institute of Technology in Pasadena, Calif.

Using a suite of advanced instruments that measure particle sizes and numbers, they traced copious numbers of aerosol particles to minute concentrations of the iodine compound, well within levels often present along the coast.

"This is a new mechanism to produce particles over the ocean that can form clouds and affect climate," Kolb told UPI. "We wouldn't know how important it is until we make more field and laboratory measurements to better understand how widespread and effective it is."

Over the next two months, investigators from 12 European and U.S. centers will be flying over the Irish coast in a survey they hope will start providing an answer to those questions.

Aerosols come in two main forms. Primary aerosols, made infamous by the likes of smoke from fires, soot and ash from factories, emissions from motor vehicles, boats and planes and airborne dust, spew their poison directly into the atmosphere.

Secondary aerosols, generated from gaseous pollutants in exhaust outpourings and emissions from land vegetation and marine organisms, arise in the atmosphere itself. Photochemical processes in urban smog are known to produce high levels of such secondary particles.

The aerosol effect can take numerous forms, such as depleting the ozone layer, forming acid rain, affecting human health, reducing visibility and influencing climate.

Over the oceans, the main chemical source of these aerosols was thought to be the co-condensation of sulphuric acid vapor and water vapor. Now, it seems that iodine oxides may also belong on the list, the authors said.

"The obvious task that remains is to determine just how widespread this newly identified mechanism of particle growth is," Kolb said. "To have a significant influence on climate, it would have to be effective over the oceans as a whole, not just in the coastal environment."

The study will undoubtedly spur more research in the field, he said.

"The world is a complicated place and we need to keep working hard to understand how it works," Kolb told UPI. "If we don't, our species may find it much less habitable in the future."

The research is reported in the June 6 issue of the journal Nature.