Application for a Newly Developed High-Capacity NO_x Denuder: Low-NO_x Diesel Transformation Experiments

ABSTRACT

To conduct low oxides of nitrogen (NO_x) chamber experiments with modern diesel emissions (DE), a high-capacity NO_x denuder was developed and used at the European Photoreactor (EUPHORE) outdoor simulation chamber. The denuder displayed a sufficient NO_x storage capacity for use with DE, and efficient removal of NO_x during injections of DE was achieved (>98%). Degradation of the denuder performance after repeated regeneration by heating (400 °C) and flushing with an air/oxygen ratio of 2:1 was not observed for a total of nine experiments. Evaluation of dark (with chamber cover closed) experiments (four in total) with and without the denuder in-line revealed some reduction (22%) of diesel particulate matter (DPM) with use of the denuder, most likely a result of impaction or settling of DPM during DE transit. However, DPM reduction may have also been a result of reductions in effective load of the engine-dyno system during the DE injections. Extensive chemical characterization of DPM revealed no significant perturbation of major compound groups associated with denuder use, except for nitrated polyaromatic hydrocarbon (NPAH) concentrations. The implications of high-NO_x experiments without the use of a NO_x denuder are discussed.

IMPLICATIONS

Achieving DPM mass concentrations appropriate for chemical analysis and toxicity evaluations in DE transformation experiments requires injection of a relatively large volume of modern DE into a chamber of known volume, leading to an unrealistically high mixing ratio of NO_x (mostly as nitric oxide). The high NO_x levels result in chamber atmospheres that are photochemically inhibited and therefore not relevant to transformations that may occur in the ambient atmosphere during aging. Successful application of a newly developed high-capacity NO_x denuder for DE transformation experiments was achieved at the EUPHORE outdoor simulation chamber. Chemical characterization of experimental samples with and without the denuder in-line and the implication of high-NO_x chamber atmospheres for NPAH concentrations are discussed.

ACKNOWLEDGMENTS

The authors acknowledge Dr. Fred Rogers, Larry Sheetz, and Rick Purcell for their contribution throughout the experimentation and development stages. In addition, staff at the Organic Analytical Laboratory at the Desert Research Institute and the Fundación Centro de Estudios Ambientales del Mediterráneo were very helpful in providing needed support at crucial moments. The Health Effects Institute funded this work.