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 (Ͼ98%). 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. INTRODUCTIONModern light-duty diesel engines emit relatively low vapor and particulate emissions in comparison to older engine models. 1 At the same time, oxides of nitrogen (NO x , or nitric oxide [NO] ϩ nitrogen dioxide [NO 2 ]) emissions from these engines have not changed significantly (frequently in the range of 300 -500 parts per million [ppm]), which presents a challenge when performing chamber experiments based on pseudoambient dilution ratios (Ն300 -400:1). To achieve diesel particulate matter (DPM) mass concentrations appropriate for chemical analysis and toxicity evaluations, a relatively large volume of modern diesel emissions (DE) must be introduced into a chamber of known volume, leading to an unrealistically high mixing ratio of NO x . In such conditions, the formation of major atmospheric oxidants (hydroxyl [OH] radical, ozone ]O 3 ], nitrate [NO 3 ] radical) will be extremely low, with rapid removal from the system through reactions with NO to form NO 2 and nitric acid (HNO 3 ). The photochemical transformation of organic compounds resulting from primary emissions would be effectively shut down, making experiments carried out in sunlight inefficient. 2 Therefore, a NO x removal (denudation) technology is crucial to carry out low-NO x experiments while achieving necessary in-chamber DPM concentrations.This study of atmospheric transformations of DE 3 pursued the development and optimization of a NO x denuder that would be able to reduce high NO x concentrations before chamber infusion. The study was carried out in 2005/2006 at the European Photoreactor (EUPHORE) outdoor simulation chamber in Valencia, Spain. 4 -6 The aim was to evaluate changes in chemistry and toxicity resulting from the aging of DE in different chamber atmospheres. To achieve in-chamber mass con...

Emissions of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs from heavy-duty diesel vehicles with DPF and SCR

“…Difference between the results from single sample and accumulated sample will indicate the potential artifact due to sampling duration (Zhang and McMurry, 1991). The presence of NO 2 in the sampling air (exhaust) may result in sampling loss of PAHs collected on the filter, which will depend on the level of NO 2 in the exhaust and the mass loading of PAHs on the filter (Carrara and Niessner, 2011;Samy et al, 2011). The potential artifacts due to NO 2 oxidation are further discussed in the following section.…”

“…The detection limit in nanograms per sample for the mass of each PAH on the filter was obtained by multiplying the MDL in ng/µL with the sample extraction volume, which can range from 0.03 ng to 5 ng depending upon the solvent purity, background interferences, and analytical conditions (variation of final extraction volume and GC injection volume). A portion of the filters was also analyzed for nitro-PAHs in particle phase by Desert Research Institute (DRI) using previously published methods (Zielinska et al, 2004b;Samy et al, 2011). Due to the addition of the NO 2 group the nitro-PAHs have lower vapor pressures than their parent PAHs.…”