Efficient determination of vehicle emission factors by fuel use category using on-road measurements: downward trends on Los Angeles freight corridor I-710

摘要

To evaluate the success of vehicle emissions regulations, trends in bothfleet-wide average emissions as well as high-emitter emissions are needed,but it is challenging to capture the full spread of vehicle emission factors(EFs) with chassis dynamometer or tunnel studies, and remote sensing studiescannot evaluate particulate compounds. We developed an alternative methodthat links real-time on-road pollutant measurements from a mobile platformwith real-time traffic data, and allows efficient calculation of both theaverage and the spread of EFs for light-duty gasoline-powered vehicles (LDG)and heavy-duty diesel-powered vehicles (HDD). This is the first study inCalifornia to report EFs under a full range of real-world driving conditionson multiple freeways. Fleet average LDG EFs were in agreement with mostrecent studies and an order of magnitude lower than observed HDD EFs. HDDEFs reflected the relatively rapid decreases in diesel emissions that haverecently occurred in Los Angeles/California, and on I-710, a primary routeused for goods movement and a focus of additional truck fleet turnoverincentives, HDD EFs were often lower than on other freeways. When freeway emissionrates (ER) were quantified as the product of EF and vehicle miles traveled (VMT) per timeper mile of freeway, despite a two- to three-fold difference in HDDfractions between freeways, ERs were found to be generally similar inmagnitude. Higher LDG VMT on low HDD fraction freeways largely offsetthe difference. Therefore, the conventional assumption that freeways withthe highest HDD fractions are significantly worse sources of total emissionsin Los Angeles may no longer be~true.