Scientists know relatively little about particles released into the air when a vehicle driver brakes, though evidence suggests those particles may be more harmful to health than particles exiting the tailpipe. In a new study in Proceedings of the National Academy of Sciences, University of California, Irvine researchers show how most of these aerosol particles emitted from braking are electrically charged. The team used a large lathe to spin a detached brake rotor and caliper, then measured the electric charge of the aerosols e