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.

Please refer to the following manuscript:

Thomas, A. E., Bauer, P. S., Dam, M., Perraud, V., Wingen, L. M., and Smith, J. N.: Automotive braking is a source of highly charged aerosol particles, Proc. Natl. Acad. Sci., 2023, submitted. 

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