Non-exhaust traffic emissions: Sources, characterization, and mitigation measures

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Transportation Engineering

Background:

• Non-exhaust emissions (NEE) from vehicle components (brakes, tires) and road dust resuspension constitute up to 90% of traffic-related particulate matter (PM).
• Existing research on NEE is characterized by highly variable and incomparable results due to diverse sources and a lack of standardized measurement protocols.
• Resuspended road dust is identified as the predominant NEE source, with emission factors varying significantly across studies.

Purpose of the Study:

• To review and analyze current knowledge on road traffic NEE, covering sources, particle generation, characterization, and mitigation.
• To highlight the challenges posed by the heterogeneity of NEE sources and the absence of standardized monitoring methods.
• To identify the need for improved and further investigated mitigation and prevention strategies for NEE.

Main Methods:

• Literature review and analysis of existing studies on non-exhaust emissions from road traffic.
• Compilation and comparison of emission factors for various NEE sources, including brake wear, tire wear, and resuspended dust.
• Assessment of the effectiveness and limitations of current mitigation and prevention strategies.

Main Results:

• Emission factors for brake wear range from 1–18.5 mg km⁻¹ veh⁻¹, and for tire wear from 0.3–7.4 mg km⁻¹ veh⁻¹.
• Resuspended dust shows highly variable emission factors, ranging from 5.4–330 mg km⁻¹ veh⁻¹ for cars, confirming it as a primary NEE contributor.
• Current mitigation strategies like street washing are effective short-term solutions, while electric vehicles present potential NEE challenges due to battery weight.

Conclusions:

• The lack of standardized monitoring protocols hinders the establishment of international regulations for NEE control.
• Existing mitigation strategies require further investigation and improvement for long-term effectiveness.
• Future research should focus on standardizing methods, developing regulations, and enhancing technologies to effectively reduce non-exhaust particulate matter emissions.