EARPA Position Paper - Non Exhaust Particle Emissions - Gaps and Research Needs

Abstract

Non-Exhaust Emissions (NEE)—mainly from brakes, tires, and road wear—have become the dominant source of transport-related particulate matter (PM) pollution as exhaust emissions decline. Today, NEE account for over 90% of road transport PM₁₀ and 80% of PM₂.₅. While electrification reduces tailpipe emissions, Battery Electric Vehicles (BEVs) may increase tire and brake wear due to their higher weight, partly offsetting environmental gains.

New regulations under Euro 7 will introduce the world’s first brake emission limits for passenger BEVs from 2026–2027 and phased tire abrasion standards from 2028 onward. However, airborne tire emissions and Heavy-Duty Vehicle (HDV) non-exhaust emissions remain insufficiently regulated, with standards for HDVs only expected after 2030.

Several mitigation technologies show promise:

Regenerative braking in BEVs can reduce brake wear particles by up to ~90%. Low-wear brake materials, such as tungsten carbide coatings or carbon-ceramic discs, significantly lower PM emissions. Tire wear capture systems and smoother driving practices can reduce emissions substantially. Road surface innovations, such as rubber-modified asphalt, may halve tire and road wear particle generation.

Despite progress, major knowledge gaps remain:

The health impacts of nanoparticles (<100 nm) and volatile particles are poorly understood and not adequately captured by current PM mass-based regulations. Most brake and tire particles are non-airborne, contaminating soil and water systems with limited regulatory attention. Significant uncertainty exists around chemical composition, source attribution, aging, and secondary particle formation. HDV emissions remain understudied and lack standardized measurement methods.

Methodological limitations also hinder progress. Current laboratory tests poorly represent real-world driving conditions, temperature effects, and whole-vehicle interactions, while field measurements face contamination challenges and lack harmonized protocols.

The paper recommends a coordinated research agenda focused on:

Health and environmental impact assessment, especially nanoparticles and ecosystem contamination. Improved measurement methods, including real-world campaigns, whole-vehicle testing, harmonized standards, and HDV methodologies. Emission reduction strategies, such as lightweight materials, optimized driving behavior and vehicle control, improved tire/brake materials, climate-adapted solutions, and road surface improvements.

The overall message is that NEE are an increasingly critical air quality and public health challenge. While EU-funded projects and Euro 7 regulations are important steps, sustained research and investment beyond current programs will be necessary to develop effective long-term solutions.