Enhancing near-road exposure assessment

摘要

Non-tailpipe particle mass (PM) emissions are formed mostly from mechanical processes, in contrast with particles from tailpipe emissions, which are formed during fuel combustion. Because of the significant reduction of tailpipe PM emissions from new technology vehicles, interest in non-tailpipe emissions of motor vehicles is increasing. The main sources of non-tailpipe PM emissions from on-road vehicles include as follows: generation by abrasion of brakes and tires, generation by abrasion of the road surface, and re-suspension from the road surface (called road dust). Particles from non-tailpipe sources differ from those associated with tailpipe emissions in both composition and size distribution. Their size is generally larger than tailpipe particles, although such particles have less carbonaceous material and a higher metallic content (Liati et al. 2019; Nosko, Vanhanen, and Olofsson 2017). Specific chemical species considered to be tracers of non-tailpipe emissions include barium (Ba), copper (Cu), antimony (Sb), iron (Fe), and zinc (Zn) that are derived mostly from brake lining, pads, and rotors, as well as Zn and benzothiazoles for tire wear emissions (Grigoratos and Martini 2015; Denier van der Gon et al. 2013). Study of non-exhaust emissions is challenging because the composition of brakes and tires is highly variable, generally proprietary, constantly changing, and differs by application (e.g., light vs. heavy duty vehicles, traditional vs. low rolling resistance tires, new vs. retreaded tires). For example, Cu and certain other components are being phased out of brake pads as the result of a Memorandum of Understanding among the United States Environmental Protection Agency and various affiliated industry organizations (US EPA 2015). Furthermore, the composition of materials used to build roads, their wear, and the dispersal of dust from surrounding areas is variable.