In this study, the emission factors of PM10 and its chemical constituents from various contributing sources including nontailpipe and tailpipe emissions were estimated on two interstate freeways in the Los Angeles basin. PM10 samples were collected on the I-110 and I-710 freeways as well as at the University of Southern California (USC) campus as the urban background site, while freeway and urban background CO2 levels were measured simultaneously. PM10 samples were analyzed for their content of chemical species which were used to estimate the emission factors of PM10 and its constituents on both I-110 and I-710 freeways. The estimated values were employed to determine the emission factors for light (LDV) and heavy-duty vehicles (HDV). The quantified species were also processed by the positive matrix factorization (PMF) model to produce PM10 freeway source profiles and their contribution to PM10 mass concentrations. Using the PMF factor profiles and emission factors on the two freeways, we characterized the emission factors for light-duty and heavy-duty vehicles by each nontailpipe source. Our findings indicated higher nontailpipe emission factors of PM10 and metal elements on the I-710 freeway compared to the I-110 freeway, due to the higher fraction of heavy-duty vehicles (HDVs) on that freeway. Furthermore, the generation of nontailpipe PM10 from resuspension of road dust was twice of tire and brake wear. The results of this study provide significant insights into PM10 freeway emissions and particularly the overall contribution of nontailpipe and tailpipe sources in Los Angeles, which can be helpful to modelers and air quality officials in assessing the importance of individual traffic-related emissions on the overall population exposure.
Keywords: PM10 emission factor; nontailpipe emissions; resuspended dust; tailpipe emissions; tire and brake abrasion.