Vehicles emit inhalable particulates from two major sources: the exhaust system, which has been extensively characterized and regulated; and non-exhaust sources including brake-wear, tire-wear, and road dust resuspension. Increasingly stringent standards for exhaust emissions have led to the non-exhaust fraction becoming increasingly important. Model predictions (both MOVES and EMFAC) suggest that traffic-related emissions of both PM2.5 and PM10 from non-exhaust sources are currently on par with exhaust sources and will continue to increase in importance. Additionally, there is a growing concern over their potential toxicity due to their high metal content. Given the increased relevance of non-exhaust emissions and associated health concerns, new studies are needed to better estimate their magnitude and their impact on communities situated near major roadways. A greater understanding of the physical and compositional characteristics as well as overall emissions is needed for non-exhaust sources. Currently, a laboratory project is being funded to measure brake-wear particulate matter (PM) under controlled laboratory conditions, but an additional study is needed to determine how those emissions behave in the real-world. The objective of this project is to deploy a comprehensive measurement campaign near major roadway sites to capture a variety of driving behavior and fleet compositions. Real-time instrumentation will capture transient effects and discern the influence of driving conditions (smooth freeway driving verses stop and-go) and fleet mix (light-duty vs. heavy-duty). Filter measurements will help quantify total PM mass and identify tracers of individual non-exhaust sources. The information gathered will be analyzed to derive emission factors of non-exhaust emissions and in particular individual sources such as brake and tire-wear. It will also be input into a dispersion model to validate the derived emission factors and to estimate the potential exposure of downwind communities to these PM sources. The University of California, Riverside (UCR) proposes to deploy a comprehensive suite of instruments designed to detect PM in a wide size range as well as tracers unique to the individual non-exhaust sources. The results of this project will be compared to current and future laboratory tests measuring brake and tire-wear PM under controlled conditions to determine how representative they are of the real-world. This project will develop a standardized experimental protocol to measure non-exhaust PM near roadways and will be used as a benchmark measurement for comparison with future campaigns when it is expected that non-exhaust influence may increase relative to exhaust. The results will also be compared to the updated EMFAC emission factors generated from the laboratory measurements. Thus, this work will have important implications for our ability to predict the impact of these emissions on communities living near roadways.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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