Electrical Charge Characteristics of Brake Wear Aerosol

ADAM THOMAS, Paulus Bauer, Michelia Dam, James Smith, University of California, Irvine

     Abstract Number: 262
     Working Group: Urban Aerosols

Abstract
The last few decades have seen a reduction in tailpipe emissions from roadways across the nation, but there nevertheless remains a looming giant of traffic pollution found from non-exhaust sources (e.g., brake and tire wear) that, until recently, has received little attention from the atmospheric science community. Aerosol particles generated from the wear of automotive brake pads contribute to roughly half the particulate mass attributed to these non-exhaust emissions, and their relative contribution to urban air pollution will almost certainly increase as fossil fuels are phased out in the coming decades. In order to better understand the atmospheric implications of their growing prominence, a more rigorous description of their physicochemical properties is needed. The presence of electrical charges on aerosol particles have previously been shown to influence atmospheric lifetimes and coagulation characteristics, thus potentially impacting their ability to serve as seeds for cloud droplet formation. Herein, we describe the first reported measurements on the electrical charge characteristics of brake wear particles. A custom built brake dynamometer was used to generate particles emitted from two widely used types of brake pads. Electrical charge state, as observed for particles of both polarities, was probed using tandem differential mobility analysis, while the total aerosol current and charged particle fraction were also measured. We find that 40-80% of brake wear particles are charged under moderate braking conditions, depending on the brake type. Negatively charged brake wear particles are more numerous than positive, and particles of both polarities are multiply charged, with some carrying as many as 20 elementary charges. In addition to affecting our understanding of how brake wear aerosol behaves in the atmosphere, our findings should also help inform future containment strategies that aim to exploit these particles’ electrical properties.