A study of the relationship between rear-of-wheel particle emissions and close-proximity tire/road noise of a passenger car.

Non-exhaust particulate emissions and road traffic noise will continue to constitute significant threats to the environment and human health during the 21st century. In the EU alone, >60 million adults are subjected to unhealthy levels of vehicle noise, while over 200,000 premature deaths are caused by chronic exposure to excessive concentrations of fine particles, with road traffic being a key source. Although these pollutants share common sources and can affect the same targets, studies have often treated their emissions separately. This study establishes both the phenomenological and mathematical relationships between tire/road noise (TRN) and rear-of-wheel particle (RoWP) emissions. Information from test track measurements, coupled with correlation-based models, enables linking TRN with RoWP emissions through variables such as vehicle speed and pavement properties, including macro-texture scales. A careful examination of the data reveals that pavement macro-texture acts as a crucible in which TRN and RoWP emissions are generated in an interrelated manner. However, at speeds over 70-80 km/h, the depletion of readily mobilizable RoWP fractions, followed by the emergence of refractory (hard-to-mobilize) circum-/super-micron RoWP fractions from resuspension (which accompanies the intensification of air-pumping TRN generation mechanisms), marks a loss of this interdependence. These results, supplemented by valuable insights into the particulate emission performance of pavements, serve to outline future air quality challenges and provide a basis for the simplified monitoring and control (e.g. through acoustic measurements) of RoWP emissions.