Research Program Area: Emissions Monitoring & Control
This final report presents the investigation results of the CARB vehicle emissions study, with focus on the physicochemical and toxicological properties of the semi-volatile and non-volatile fractions of PM from heavy duty diesel vehicles, operating with and without emissions control technologies. A wide variety of diesel fuelled vehicles, representing the current in-use fleet, have been tested in the California Air Resources Board’s (CARB) heavy-duty diesel emission testing laboratory (HDETL) in downtown Los Angeles, including a 1998 Kenworth truck, a diesel hybrid electric bus, a school bus, and a Caltrans truck on three driving cycles, i.e. steady state cruise (50mph), transient [EPA urban dynamometer driving schedule (UDDS)] and idle to simulate various real-world driving conditions. The tested emission control devices include a Continuously Regenerating Technology (CRT); CRT in combination with a selective catalytic reduction system (Zeolite or vanadium based SCRTs) etc. Detailed physico-chemical and toxicological characteristics of PM were measured for each vehicle and driving cycle, including physical properties (e.g. PM mass and size distribution), chemical (EC, OC, organic compounds, trace elements, inorganic ions) and toxicological [dithiothreitol (DTT) and macrophage reactive oxygen species (ROS)assays] characterization of the collected PM samples.
Substantial reduction in PM mass emissions ( > 90%) was accomplished for the tested vehicles operating with advanced emission control technologies, while such a reduction was not observed for particle number concentrations under cruise conditions, with the exceptions of the Hybrid-CCRT and EPF vehicles. Significant reductions in the emission of major chemical constituents (TC, OC, EC, and organic compounds) were achieved by the introduction of retrofits. Sulfate dominated the PM composition in vehicle configurations (V-SCRT-UDDS, Z-SCRT-Cruise, CRT, DPX) with considerable nucleation mode and total carbon was dominant for the configurations with less (ZSCRT-UDDS) or insignificant (CCRT, Horizon) nucleation. V-SCRT and Z-SCRT effectively reduced PAHs, hopanes and steranes, n-alkanes and acids by more than 99%, and often to levels below detection limits for both cruise and UDDS cycles. The CRT technology also showed similar reductions with SCRT for medium and high molecular weight PAHs, acids, but with slightly lower removal efficiencies for other organic compounds. Despite an increase in the intrinsic activity (both DTT and ROS, per mass basis) of exhaust PM with use of most control technologies, the overall activity (expressed per km or per hr) was substantially reduced for retrofitted configurations compared to the baseline vehicle. Significant reduction in DTT activity (by 50-100%) was observed for thermally-denuded PM from vehicles with retrofitted technologies (PM with significant semi-volatile fraction). On the other hand, Chelex treatment of PM samples removed a substantial (≥70%) fraction of the ROS activity, corroborating the effect of transition metals on this activity. Correlation analysis performed between measured activity and the chemical constituents showed that DTT activity is strongly associated (R=0.94) with the water soluble organic carbon (WSOC), while the ROS activity was mostly driven by Fe content of the PM samples.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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