Abstract: 

Aerosol particles are ubiquitous in the atmosphere and their emissions have important implications on human health and climate globally. Emission pathways include primary processes where particles are emitted directly into the atmosphere, and secondary processes where they are formed from the chemistry of gases in air.  While particle emissions from motor vehicles have reduced significantly over the last decades coinciding with the ongoing transition to alternative fuels and vehicle electrification, non-exhaust vehicular sources such as brake and tire wear are quickly emerging as the predominant traffic pollutants.  Understanding the implications of this growing prominence on air quality and climate depends on a thorough knowledge of their physical and chemical properties.  Here we present two investigations on brake wear particle emissions as simulated using a custom-built brake dynamometer.  The first examines the electric charge state of primary emissions observed under moderate or light braking conditions, while the second reports on the organic composition of secondary particles formed under heavy braking conditions.  Intriguing implications of these findings on future emission containment efforts and the potential climate impacts of this aerosol source of emerging significance are discussed.