Nitric acid-nitrate aerosol measurements by a diffusion denuder: A performance evaluation

Application for a newly developed high-capacity NOx denuder: low-NOx diesel transformation experiments

To conduct low oxides of nitrogen (NOx) chamber experiments with modern diesel emissions (DE), a high-capacity NO, denuder was developed and used at the European Photoreactor (EUPHORE) outdoor simulation chamber. The denuder displayed a sufficient NOx storage capacity for use with DE, and efficient removal of NO, during injections of DE was achieved (>98%). Degradation of the denuder performance after repeated regeneration by heating (400 degrees 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-NOx experiments without the use of a NOx denuder are discussed.

Measurement of Atmospheric Pollutants Relevant to Dry Acid Deposition

The transfer of acid gases and particles from the atmosphere to the earth's surface, where they exert adverse environmental effects, is called acid deposition. Relevant removal processes occur during dry weather conditions, during the formation of clouds or by scavenging of falling rain or other hydrometeors. The first removal process is called acid dry deposition while the last two, known as rainout and washout, respectively, are lumped together into the phenomenon of acid wet deposition.