Data for: Automotive braking is a source of highly charged aerosol particles

Although the last several decades have seen a dramatic reduction in
emissions from vehicular exhaust, non-exhaust emissions (e.g., brake and
tire wear) represent an increasingly significant class of traffic-related
particulate pollution. Aerosol particles emitted from the wear of
automotive brake pads contribute roughly half of the particle mass
attributed to non-exhaust sources, while their relative contribution to
urban air pollution overall will almost certainly grow, coinciding with
vehicle fleet electrification and the transition to alternative fuels. To
better understand the implications of this growing prominence, a more
thorough understanding of the physicochemical properties of brake wear
particles (BWPs) is needed. Here we investigate the electrical properties
of BWPs as emitted from ceramic and semi-metallic brake pads. We show that
up to 80% of BWPs emitted are electrically charged, and demonstrate a
dependence of charge state on particle size and charge polarity. We find
that brake wear produces both positive and negative charged particles that
can hold in excess of 30 elementary charges, and show evidence that more
negative charges are produced than positive. Our results will provide
insights into the currently limited understanding of how BWPs behave in
the atmosphere, including future investigations into their atmospheric
lifetimes and potential climatic relevance. In addition, our study will
inform future efforts to remove BWP emissions before entering the
atmosphere by taking advantage of their electric charge.