Israeli factory
©Ariel Jerozolimski [file]
Ramat Hovav, in southern Israel

A certain number of aerosol particles in the air increases rainfall, but an overabundance of them retards it, according to new research by a group of international scientists, led by Prof. Daniel Rosenfeld of the Institute of Earth Sciences at the Hebrew University of Jerusalem.

The team developed a model that shows how particles in the air influence cloud formation and rain. The findings were published Friday in the latest issue of the journal Science.

Tiny floating particles, known as aerosols, significantly influence cloud formation. While they occur naturally, they are also produced through human action. As pollution rises, the aerosol particles produced can tip the natural balance.

While some aerosol particles form the nuclei of the clouds themselves, too many aerosols act as a sunblock, keeping water from evaporating to form clouds.

"Both camps are right," said Prof. Meinrat O. Andreae, director of the Max Planck Institute for Chemistry in Germany, a coauthor of the publication. "But you have to consider how many aerosol particles there are."

Lead author Rosenfeld added: "The amount of aerosols is the critical factor controlling how the energy is distributed in the atmosphere."

The research team discovered that there was a specific
curve to the production: rainfall first rises, then plateaus and then sharply drops off in the presence of too many aerosols.

"These results have great significance for countries like Israel, where rainfall is scarce and can be easily affected by over-production of aerosols," Rosenfeld said. "Our study should act as a red light to all of those responsible for controlling the amounts of pollution we release into the atmosphere."

According to Andreae, "With these results we can finally improve our understanding of aerosol effects on precipitation and climate, since the direct contradiction of the different aerosol effects has seriously hindered us from giving more accurate predictions for the future of our climate and especially for the availability of water."