May 19, 2009

Biological particles found in high clouds

U.S. scientists say they've made the first direct observations of biological particles in high-altitude clouds.

A team of atmospheric chemists led by Kimberly Prather and Kerri Pratt of the Scripps Institution of Oceanography at the University of California-San Diego sampled water droplet and ice crystal residues at high speeds while flying through clouds in the skies over Wyoming.

An analysis revealed the particles were made up nearly entirely of either dust or biological material, such as bacteria, fungal spores and plant material. While it's long been known microorganisms become airborne and travel great distances, the researchers say their study is the first to yield direct data on how microorganisms work to influence cloud formation.

The scientists said their findings suggest biological particles that get swept up in dust storms help to induce the formation of cloud ice, and that their region of origin makes a difference. For example, they said, evidence is increasingly suggesting that dust transported from Asia could be influencing North American precipitation.

The National Science Foundation and National Center for Atmospheric Research-funded study is reported in the early online edition of the journal Nature Geoscience.