Aerosols to Fret About


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Tiny particles bring deadly rain

Nanobacteria have been implicated in human diseases from clogged arteries to ovarian cancer. Who would have thought that the tiny particles (one-hundredth the size of the average bacterium) might make rain too?

Physicist Andrei Sommer of the University of Ulm in Germany and mathematician N. Chandra Wickramasinghe of Cardiff University in Wales think nanobacteria are in the atmosphere. The tiny particles are often covered with a coating of sticky protein slime, which can collect water, and, Sommer says, they are “just the right size” to serve as cloud condensation nuclei—the seeds upon which raindrops grow.

If the two researchers are correct, nanobacteria originate in human bodies, where they were first discovered in kidney stones nearly a decade ago. After they are excreted in urine, they eventually turn up in wastewater streams and evaporate into the atmosphere.

Thus, rain showers could spread disease, Sommer says. It is not at all clear how nanobacteria work—or even what they are. Some researchers argue that they are bits of inert mineral; others contend they are among the world’s smallest and oldest living organisms. Experiments show they can replicate themselves, and controversial studies show they contain rudimentary genetic material. Sommer says proof they’re alive is lacking: “Their genetic content is not clear. Critics of the biological status of nanobacteria are justified.”

Only time will tell what nanobacteria really are and how much we need to worry about downpours of them, Sommer says: “Multidisciplinary efforts are now essential to estimate the threat they actually pose.”

Kathy A. Svitil

More stuff that causes showers

The air we breathe can be teeming with billions and billions of submicroscopic particles less than 1/8,000th the width of a human hair. Scientists have found about 60 percent of them are attributable to pollution, dust, ash, sand, and salt.

The rest, says atmospheric physicist Ruprecht Jaenicke of Mainz University in Germany, are mostly particles of dead organic material. Jaenicke’s 15-year study found that more than a billion tons of bioaerosols—bits of proteins and cells, animal fur, dandruff, dead plants, and insects—are sloughed off into the atmosphere every year, an amount about 20 times greater than previously estimated.

“These aerosols have an enormous impact,” says Jaenicke. The tiny particles in the atmosphere help form clouds, increase rainfall, and block sunlight. They even affect global warming. Moreover, the material is likely to cause allergic reactions. —Jocelyn Selim

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