NOx

About: NOx is a research topic. Over the lifetime, 26367 publications have been published within this topic receiving 496555 citations.

Analysis of radical propagation efficiency to assess ozone sensitivity to hydrocarbons and NO x : 1. Local indicators of instantaneous odd oxygen production sensitivity

Abstract: We used a simple trajectory model and a three-dimensional grid model to evaluate several indicators that can be used to predict the sensitivity of odd oxygen production (P(Ox)) to changes in emissions of anthropogenic nonmethane hydrocarbons (VOC) and nitrogen oxides (NOx = NO + NO2). To perform the evaluation, we augmented the model to include new diagnostic outputs such as rates of P(Ox), rates of conversion of NOx to unreactive nitrogen, and radical chain length. We used the new diagnostic outputs to explain the model-predicted sensitivity of P(Ox) to changes in VOC and NOx emissions. We found that the ozone ridgeline, which distinguishes between NOx-limited and radical-limited conditions, is determined by a ridgeline of maximum OH chain length. We examined the radical propagation reactions which affect OH chain length, and we developed four indicators related to radical propagation efficiency: I(HC,NO2) which approximates the fraction of OH that reacts with hydrocarbons; I(NO,RO2) which approximates the fraction of HO2 that reacts with NO; the ratio of [O3]/[NOx] which affects the balance between radical initiation and propagation; and [HO2] which is the dominant term in P(H2O2)/P(HNO3). Each of these indicators distinguishes conditions in which instantaneous P(Ox) is primarily sensitive to either NOx emissions reductions or VOC emissions reductions.

Reduction of lean NOx by ethanol over Ag/Al2O3 catalysts in the presence of H2O and SO2

Abstract: The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al2O3 catalysts in the presence of H2O and SO2. The Ag/Al2O3 catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to form CH3CHO, CO along with small amounts of hydrocarbons (C3H6, C2H4, C2H2 and CH4) and nitrogen compounds such as NH3 and N2O. The presence of H2O enhances the NOx reduction while SO2 suppresses the reduction. The presence of SO2 along with H2O suppresses the formation of acetaldehyde and NH3. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly enhanced in the presence of H2O. The NCO species readily reacts with NO in the presence of O2 and H2O at room temperature, being converted to N2 and CO2 (CO). Addition of SO2 suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still kept at high conversion levels in the presence of H2O and SO2 over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K.

Identification and Quantification of 4-Nitrocatechol Formed from OH and NO3 Radical-Initiated Reactions of Catechol in Air in the Presence of NOx: Implications for Secondary Organic Aerosol Formation from Biomass Burning

Abstract: Catechol (1,2-benzenediol) is emitted from biomass burning and produced from a reaction of phenol with OH radicals. It has been suggested as an important secondary organic aerosol (SOA) precursor, but the mechanisms of gas-phase oxidation and SOA formation have not been investigated in detail. In this study, catechol was reacted with OH and NO3 radicals in the presence of NOx in an environmental chamber to simulate daytime and nighttime chemistry. These reactions produced SOA with exceptionally high mass yields of 1.34 ± 0.20 and 1.50 ± 0.20, respectively, reflecting the low volatility and high density of reaction products. The dominant SOA product, 4-nitrocatechol, for which an authentic standard is available, was identified through thermal desorption particle beam mass spectrometry and Fourier transform infrared spectroscopy and was quantified in filter samples by liquid chromatography using UV detection. Molar yields of 4-nitrocatechol were 0.30 ± 0.03 and 0.91 ± 0.06 for reactions with OH and NO3 radi...