Automotive braking is a source of highly charged aerosol particles

Abstract

Although the last several decades have seen a dramatic reduction in emissions from vehicular exhaust, nonexhaust 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 nonexhaust 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 that this fraction is strongly dependent on the specific brake pad material used. A dependence of the number of charges per particle on charge polarity and particle size is also demonstrated. 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 BWPs and their charging mechanisms, which potentially have significant implications on their atmospheric lifetimes and thus their relevance to climate and air quality. In addition, our study will inform future efforts to remove BWP emissions before entering the atmosphere by taking advantage of their electric charge.

Unrecognized volatile and semi-volatile organic compounds from brake wear

“…A custom-built brake dynamometer (Fig. S1A†) 42 was used for these experiments. The facility employs a heavy-duty metal working 22′′ lathe (Lodge & Shipley) to rotate a disc brake system (rotor), spanning the torques and temperatures found in normal driving conditions.…”

Size distribution of brake wear particulate matter based on a brake dynamometer investigation

“…Brake wear particles (BWPs) have a high metal content (Sadiktsis et al, 2012;Avagyan et al, 2014;Hulskotte et al, 2014;Grigoratos and Martini, 2015;Fang et al, 2017), and contributes up to 55% to the oxidation potential of coarse atmospheric particulate matter in European cities (Daellenbach et al, 2020). And it is easy to understand that the high-emission areas of braking wear particles (such as traffic intersections and pedestrian crossings) highly overlap with areas of dense human activity (Thomas et al, 2024).found that over 80% of brake wear particles (BWPs) carry a high charge, which correlates with particle size. This high charge accelerates particle growth, alters transmission characteristics, and enhances particle attachment efficiency in the human lung.…”