June 5, 2025
As engine technologies improve and tailpipe emissions decline, attention is shifting to other sources of vehicle-related pollution. Researchers at UC Riverside’s Center for Environmental Research and Technology (CE-CERT) are studying brake and tire wear emissions, which are becoming increasingly important sources of small airborne particles that can affect air quality and health. These pollutants are especially concerning in high-traffic urban areas where small airborne particles can potentially increase exposure for nearby populations.
A research team led by Professor Georgios Karavalakis, Dr. Zisimos Toumasatos, and graduate students Elizabeth DeFrance, Ziao Wang, and Zixuan Gong is conducting laboratory and on-road testing to measure these non-exhaust emissions directly from vehicle brakes and tires. The team has designed and fabricated novel, fully enclosed and semi-enclosed sampling systems that have been installed in vehicles to measure brake and tire wear particulate emissions.
Real-world testing is being conducted with the test vehicles on routes in the South Coast Air Basin that represent typical urban and highway driving conditions. This project captures emissions in real-world driving environments, accounting for different driving dynamics, traffic, elevation changes, stop-and-go conditions, and road material (asphalt versus concrete). The project includes testing of four common types of brake pads and six tire models, chosen based on market analysis surveys.
The research team employs comprehensive measurements and state-of-the-art real-time equipment, including a High-Resolution Electrical Low Pressure Impactor (HR-ELPI+) and a DustTrak aerosol monitor, as well as offline analyses to determine the gravimetric PM2.5 and PM10 emissions and the chemical and toxicological properties of PM emissions.
Future phases of the study will examine gases released from the off-gassing of tires, including compounds such as polycyclic aromatic hydrocarbons and organic rubber compounds, and secondary aerosol forming potential. Tire gaseous emissions are not yet well-documented, but they may contribute to secondary organic aerosol formation, as well as pose potential health risks.
The data collected through this study will help fill a critical gap in emissions inventories by providing real-world measurements of pollutants that have long been underrepresented in regulatory frameworks. As regulatory agencies shift their focus beyond tailpipe emissions, CE-CERT’s research delivers the technical foundation needed to guide science-based policy, improve air quality models, and protect public health.
This work is supported in part by the California Air Resources Board (CARB), the Center for Advancing Research in Transportation Emissions, Energy, and Health (CARTEEH), the National Science and Technology Council (NSTC), and industry partners.