Tailpipe and Nontailpipe Emission Factors and Source Contributionsof PM10on Major Freeways in the Los Angeles Basin

In this study, the emission factors of PM10and itschemical constituents from various contributing sources includingnontailpipe and tailpipe emissions were estimated on two interstatefreeways in the Los Angeles basin. PM10samples were collected onthe I-110 and I-710 freeways as well as at the University of SouthernCalifornia (USC) campus as the urban background site, while freewayand urban background CO2levels were measured simultaneously.PM10samples were analyzed for their content of chemical specieswhich were used to estimate the emission factors of PM10and itsconstituents on both I-110 and I-710 freeways. The estimated valueswere employed to determine the emission factors for light (LDV) andheavy-duty vehicles (HDV). The quantified species were alsoprocessed by the positive matrix factorization (PMF) model toproduce PM10freeway source profiles and their contribution to PM10mass concentrations. Using the PMF factor profiles andemission factors on the two freeways, we characterized the emission factors for light-duty and heavy-duty vehicles by eachnontailpipe source. Ourfindings indicated higher nontailpipe emission factors of PM10and metal elements on the I-710 freewaycompared to the I-110 freeway, due to the higher fraction of heavy-duty vehicles (HDVs) on that freeway. Furthermore, thegeneration of nontailpipe PM10from resuspension of road dust was twice of tire and brake wear. The results of this study providesignificant insights into PM10freeway emissions and particularly the overall contribution of nontailpipe and tailpipe sources in LosAngeles, which can be helpful to modelers and air quality officials in assessing the importance of individual traffic-related emissionson the overall population exposure