California Air Resources Board

Principal Investigator/Author: Heejung Jung

Contractor: University of California, Riverside

Contract Number: 18RD017

Project Status: Completed

Relevant CARB Programs: Mobile Source Emissions, Health and Exposure

Topic Areas: Non-Exhaust Emissions, Toxic Air Contaminants, Monitoring, Modeling

Research Summary:

Non-exhaust emissions, including brake and tire-wear particles, have become more significant contributors to traffic-related PM emissions as exhaust emissions have steadily decreased. Thus, it is important to understand their contribution to local and regional air quality and their impact on roadside exposure and health effects. This research has measured PM samples at upwind and downwind locations near two major highways: one for truck and car mixed fleet on I-710 (Long Beach Location) and one for car dominant fleet on I-5 (Anaheim Location) in Southern California and evaluated chemical and physical characteristics of the samples such as elements/organic matter and particle size, respectively, which were used for source apportion analysis. Source apportionment analysis showed that the contribution from non-exhaust sources to the roadside PM2.5 was 1 -1.5 times that of primary exhaust PM2.5 (i.e., without including secondary PM2.5 formed downwind of the near roadway locations). The relative magnitude of the non-exhaust and direct exhaust PM emissions measured is in good agreement with the emission inventory (EMFAC2021) estimation, in which brake and tire-wear PM2.5 emissions are 1.3 times greater than the exhaust emission in 2020. In the study, non-exhaust PM10 emissions were 2-3 times direct exhaust PM10 emissions. It is worth noting that a large amount of the coarse PM was identified as road dust, including pavement materials, soil dust, etc. In addition to exhaust and non-exhaust PM, road dust should be considered in future investigations of health effects on the near-road communities.

Keywords: non-exhaust emissions, brake and tire wear, particulate matter (PM), emissions, exhaust, roadside exposure, health effects, highways, PM2.5, brake wear, tire wear