Microphysics of Ultrafine Particles from Regenerative Braking in Heavy-Duty Trucks

The transition to zero-emission and hydrogen-powered heavy-duty trucks (HDTs) is expected to substantially reduce tailpipe emissions, but it also increases the relative importance of non-exhaust emissions, particularly from brake wear. Regenerative braking systems significantly reduce the overall mass of brake-derived particles; however, they do not eliminate emissions entirely. The remaining ultrafine particles (UFPs), which are most relevant for human health, remain poorly understood—especially in terms of their formation, transformation, and transport in near-road environments.

This project addresses this critical knowledge gap by investigating the microphysical evolution of brake-generated UFPs under regenerative braking conditions in HDTs. The research focuses on developing a predictive understanding of how these particles evolve after emission, with particular attention to the interaction between fluid dynamics and particle-scale processes.

The specific objectives are to:

• Develop a coupled modeling framework to predict the microphysical evolution of UFPs emitted during HDT regenerative braking,
• Investigate the competition between fluid dynamic and microphysical timescales governing particle transformation,
• Quantify a Damköhler number for UFP aging to classify distinct particle evolution regimes.

By establishing the first predictive framework for the aging of brake-wear UFPs, this project will enable more accurate, health-relevant exposure assessments—such as lung-deposited surface area (LDSA)—for communities located near high-volume freight corridors. The results will provide critical insight into an emerging emissions source and inform future strategies for mitigating the environmental and public health impacts of next-generation freight systems.