Science – he Amazon rainforest makes its own rain. That’s the conclusion of a new study, which finds that microscopic bits of potassium-rich salt spewed skyward by trees and fungi may be seeding much of the region’s precipitation. Because aerosols also scatter light back into space, they can cool Earth’s surface as well.
Unless temperatures are extremely cold, raindrops don’t just form in thin air; molecules of water vapor must actually aggregate around a tiny core. Those seeds can either be particles such as mineral dust, soot, salt spray from the ocean—even airborne bacteria—or droplets such as the sulfur dioxide spewed by volcanoes. Scientists previously knew that the organic-rich particles of haze floating above the Amazon Basin acted as the seeds for much of the rainfall there, but what had served to trigger the growth of those particles—known scientifically as secondary organic aerosols—was a big mystery, says Christopher Pöhlker, an atmospheric chemist at the Max Planck Institute for Chemistry in Mainz, Germany.