NOx

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

Reactive nitrogen distribution and partitioning in the North American troposphere and lowermost stratosphere

Abstract: A comprehensive group of reactive nitrogen species (NO, NO2, HNO3, HO2NO2, PANs, alkyl nitrates, and aerosol-NO3) were measured in the troposphere and lowermost stratosphere over North America and the Atlantic during July/August 2004 (INTEX-A) from the NASA DC-8 platform (0.1-12 km). Less reactive nitrogen species (HCN and CH3CN), that are also unique tracers of biomass combustion, were also measured along with a host of other gaseous (CO, VOC, OVOC, halocarbon) and aerosol tracers. Clean background air as well as air with influences from biogenic emissions, anthropogenic pollution, biomass combustion, and stratosphere was sampled both over continental U. S., Atlantic and Pacific. The North American upper troposphere was found to be greatly influenced by both lightning NO(x) and surface pollution lofted via convection and contained elevated concentrations of PAN, ozone, hydrocarbons, and NO(x). Under polluted conditions PAN was a dominant carrier of reactive nitrogen in the upper troposphere while nitric acid dominated in the lower troposphere. Peroxynitric acid (HO2NO2) was present in sizable concentrations always peaking at around 8 km. Aerosol nitrate appeared to be mostly contained in large soil based particles in the lower troposphere. Plumes from Alaskan fires contained large amounts of PAN and very little enhancement in ozone. Observational data suggest that lightning was a far greater contributor to NO(x) in the upper troposphere than previously believed. NO(x) and NO(y) reservoir appeared to be in steady state only in the middle troposphere where NO(x)/NO(y) was independent of air mass age. A first comparison of observed data with simulations from four 3-D models shows significant differences between observations and models as well as among models. These uncertainties likely propagate themselves in satellites derived NOx data. Observed data are interpreted to suggest that soil sinks of HCN/CH3CN are at best very small. We investigate the partitioning and interplay of the reactive nitrogen species within characteristic air masses and further examine their role in ozone formation.

Influence of co-cations on the formation of Cu+ species in Cu/ZSM-5 and its effect on selective catalytic reduction of NOx with NH3

Abstract: The influence of H+ and Na+ co-cations on the formation of Cu species and on NO reduction activity of Cu/ZSM-5 catalyst is investigated. 3.5Cu/0.6NaZSM-5 catalyst was significantly more active for NOx reduction with NH3 compared with 2.6Cu/HZSM-5. Catalyst characterization indicated that, the type of co-cations present in the catalyst tailors copper species redox properties, NO2 formation rate and acidity of the catalyst. Copper species in NaZSM-5, is relatively easily reducible than when present in HZSM-5. UV–vis and FTIR characterization showed the presence of a higher amount of Cu+ species in 3.5Cu/0.6NaZSM-5 compared to 2.6Cu/HZSM-5. The easily reducible copper along with Cu+ species in 3.5Cu/0.6NaZSM-5 seems to activate oxygen which reacts with NO to form NO2. The Na+ co-cations can further capture the thus produced NO2 to form intermediate surface nitrite/nitrate species, which improves the NOx conversion. The acidity measured by NH3-TPD and FTIR is needed for SCR, but not crucial for NOx conversion.

Formation of secondary organic aerosol from irradiated α-pinene/toluene/NOx mixtures and the effect of isoprene and sulfur dioxide

Abstract: [1] Secondary organic aerosol (SOA) was generated by irradiating a series of α-pinene/toluene/NOx mixtures in the absence and presence of isoprene or sulfur dioxide. The purpose of the experiment was to evaluate the extent to which chemical perturbations to this base-case (α-pinene/toluene) mixture led to changes in the gas-phase chemistry which strongly influences mass and composition of SOA and secondary organic carbon (SOC) formed. The chemical composition was examined by gas chromatography-mass spectrometry (GC-MS) and laser desorption ionization-mass spectrometry (LDI-MS). The results showed that the addition of isoprene to the base-case mixture significantly lowered the amount of toluene reacted, and thereby lowered the amount SOC produced. Simultaneous measurement of the organic NOy showed that reactions of isoprene effectively sequester NO2 by producing gas-phase organic nitrates. The addition of SO2 to the base-case mixture, while having little effect on the gas-phase chemistry, formed sulfuric acid which led to a modest enhancement of the SOC through acid-catalyzed or sulfur-incorporating reactions of α-pinene. The contribution of each hydrocarbon to the composition of the SOA was estimated using an organic tracer method. SOC from the tracer technique tended to underpredict the measured SOC, although the underprediction was especially pronounced with SO2 present. A comparison of the chromatographic results from samples of the irradiation of the α-pinene/toluene/isoprene/NOx/SO2 mixture and ambient PM2.5 showed the presence of two unique peaks that were associated with reactions of isoprene and SO2.

Effects of fuel injection parameters on emission characteristics of diesel engines operating on various biodiesel: A review

Abstract: Many researches have been carried out towards the reduction in noxious emissions from diesel engines This paper reviews the studies on the outcomes of operating parameters discrepancy on the engine emission issues carried out by various authors in different diesel engines fuelled with biodiesel from different feedstocks The main goal of this paper is to enlighten the momentous of injection parameters like injection timing and injection pressure on the engine emission characteristics This paper touches upon the advancement and retardation methods of fuel injection timing and injection pressure to inspect the engine emission indicators such as carbon monoxide, hydrocarbon, oxides of nitrogen, smoke, particulate matter and carbon dioxide contents Comparative evaluation has been conversed accompanied by apropos causes for the deviation of emission characteristics