Physicists have long puzzled over why sand grains and other small particles can build up electrical charges as they collide with one another, sometimes to the point of discharging lightning in dust storms or plumes of volcanic ash.
Now, a paper in an upcoming issue of Nature Physics suggests that particles transfer electrical charge vertically during a smashup, such that positive charges move downward and negative charges move up in the cloud.
The findings could help combat a wide variety of practical problems, such as the adhesion of charged dust to solar panels on a Mars rover or the generation of dangerous electrical discharges that sometimes occur when a helicopter takes off in the desert.
Dust clouds can create problems in grain silos, where charge sometimes builds up and leads to explosions, and in the pharmaceutical industry, where particles of ground-up drugs can become charged and not mix properly, says Hans Herrmann, a materials researcher at ETH Zurich.
Some challenges remain, such as explaining where the background electric field that charges the particles came from. But Herrmann says the work is philosophically satisfying, in answering a long-held question, and may yet have practical applications.