Emission, Transformation, and Health Impacts of vehicular non-exhaust pollutants

Vehicular non-exhaust emissions have become a dominant source of particulate pollution in urban areas. In this work, we systematically investigated the emission, transformation, and health effects of vehicular non-exhaust pollutants. Our study focused on three key aspects: (1) real-world emissions and contributions of brake wear particles (BWPs) and tire wear particles (TWPs); (2) heterogeneous aging of atmospheric reactive gases on BWP surfaces; and (3) the evolution of health impacts during atmospheric aging of BWPs and TWPs. By combining laboratory chassis-dynamometer experiments with real-world tunnel observations, we quantitatively constrained non-exhaust emissions from both controlled and actual driving conditions. A new methodology was developed to enable direct and quantitative measurement of BWP emissions on a chassis dynamometer, providing a robust experimental foundation for emission characterization. Tunnel observations under real driving conditions further allowed us to derive BWP and TWP emissions in China using both bulk-composition and single-particle source apportionment approaches, yielding mutually consistent estimates. Complementary flow-tube simulations revealed that BWP surfaces exhibit pronounced heterogeneous reactivity toward atmospheric oxidants and trace gases such as SO₂, NO₂, and O₃. Unexpectedly, these reactions led to substantial sulfate formation from SO₂ oxidation, efficient HONO production from NO₂ uptake, and rapid O₃ decomposition. Moreover, we also found that atmospheric aging by OH and O₃ considerably enhances the oxidative potential of BWPs and TWPs, implying elevated health risks following environmental transformation. Our results reveal that vehicular non-exhaust emissions not only constitute an important primary source of urban particulate matter, but also serve as highly reactive mediators in atmospheric chemistry. We highlight the urgent need to explicitly incorporate non-exhaust sources into air-quality models and account for atmospheric aging when evaluating the health burden associated with traffic-related particles.