The Advanced Collaborative Emissions Study (ACES) of 2007- and 2010-Emissions Compliant Heavy-Duty Diesel Engines: Characterization of Emissions and Health Effects

In 2001, the US Environmental Protection Agency (EPA) adopted stringent new standards for on-highway heavy heavy-duty diesel engine (HHDDE) emissions of particulate matter (PM) and oxides of nitrogen (NOx) that were to become effective during the 2007–2010 time period. The Advanced Collaborative Emissions Study (ACES) was a cooperative, multiparty effort to characterize the emissions (in Phases 1 and 2) and assess the possible health impacts (in Phase 3) of the new, advanced HHDDE technologies, after introducing them to the market. Phase 1 demonstrated that the regulated emissions from four 2007-compliant engines tested were all below the 2007 standards. Both regulated and unregulated emissions were substantially reduced relative to pre-2007 technology engines, except for nitrogen dioxide (NO2) emissions that were higher compared to 2004 technology engines due to the use of diesel oxidation catalyst (DOC) and catalyzed diesel particulate filter (DPF) exhaust aftertreatment technologies. Phase 2 showed another large step in emissions reductions for 2010-compliant diesel engines. The three 2010-compliant engines tested had substantially lower regulated emissions of NOx, CO, NMHC, and PM relative to the emission standards and also relative to the 2007-compliant engines. NOx reductions were achieved using urea-based selective catalytic reduction (SCR) and an ammonia oxidation catalyst (AMOX). A wide spectrum of particle and gas phase unregulated emissions species, including NO2, were also reduced relative to 2007-compliant engines and older engines. Phase 3 consisted of an inhalation bioassay in which rats were exposed for their lifetime to the diluted exhaust from one of the 2007-compliant engines tested in Phase 1. Three exhaust dilutions were selected based on the nitrogen dioxide (NO2) concentrations to achieve three exposure levels: 4.2 ppm (high-DE exposure), 0.8 ppm (mid-DE exposure), and 0.1 ppm (low-DE exposure) NO2. The control exposure consisted of filtered air. NO2 was chosen because the particle concentrations in the exhaust were too low to set the dilution levels. Exposures were conducted 16 h/day, 5 days/week. Rats were evaluated histopathologically and for respiratory function, a large number of noncancer endpoints, and genotoxicity, at interim time points up to the final sacrifice at 28 months (males) and 30 months (females). Histopathological analyses found that exposure to exhaust from a 2007-compliant engine produced no tumors or precancerous effects in lungs and no increase in tumor incidence outside the lung, but induced mild epithelial hyperplasia in the central acinus region of the lung, interstitial fibrosis, and bronchiolization at the high exposure level. The lung histologic changes were consistent with previous findings in rats after long-term exposure to NO2—a major component of the chamber exposure atmosphere, which is substantially reduced in 2010-compliant engines. The majority of the biological endpoints were unchanged with exposure and little inflammation was observed. In summary, the ACES study shows that emissions from 2007- and 2010-compliant HHDDE have been reduced dramatically and that exhaust from a 2007-compliant engine produced no tumors or precancerous effects in rats exposed over their lifetime.