Colliding dust grains charge each other up

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 appearing online April 11 in 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.

http://www.sciencenews.org/view/generic/id/58172/title/Colliding_dust_grains_charge_each_other_up