Major Nitrogen Species Research Articles

Land use as a major factor of riverine nitrate in a semi-arid farming-pastoral ecotone: New insights from multiple environmental tracers and molecular signatures of DOM

The nitrogen contamination in rivers has become significant concern in arid and semiarid areas due to water resource shortage and extensive anthropogenic activities in relation to land-use changes in China. As a major nitrogen species, identifying driving factors, transformation and sources of nitrate is crucial for managing nitrogen pollution in rivers. In this study, nitrate sources and transformations were deciphered using physicochemical variables, molecular signature of dissolved organic matter and coupled isotopes of nitrate under different land use types in the Yang River, a typical farming-pastoral ecotone in the semi-arid area of North China. The results of river water showed a significant positive correlation between NO3− concentrations, δ15N-NO3− values and percentage of urban land and cropland, which confirmed the critical role of land use in the variations of riverine nitrate. The correlation between dissolved organic matter composition (aliphatic and lignin-like compounds) and NO3−/Cl− ratios as well as Cl− concentrations verified the effect of agricultural activities on nitrate source and transport. The variation in water chemical variables and dual isotopes of nitrate in river and soil extracts (δ15N-NO3− and δ18O-NO3−) was indicative of the concurrence of in-soil nitrification process and assimilation, whereas denitrification was inhibited under aerobic conditions in the semiarid area. The Bayesian model revealed that about 60% of nitrate was derived from non-point sources (manure, soil organic nitrogen and chemical fertilizer) and 36% from sewage. Although urban is not the major land-use type in the farming-pastoral ecotone, sewage contributed to about 36% of nitrate. The source identification of nitrate stresses the importance of the management of non-point pollution and demand for sewage treatment facilities in the farming-pastoral ecotone. This multiple-tracer approach will help gain deeper insights into nitrogen management in semi-arid areas with extensive human disturbance.

Facile preparation of graphene nitride by irradiating MHz ultrasound

The present study aimed at developing a simple sonochemical method to prepare graphene nitride from the mixture of graphite and aqueous ammonia solution. Ultrasound of 1.6 MHz was irradiated to the sample in a fabricated sonoreactor at predetermined ultrasonic power and duration. The one-pot method succeeded in the preparation of graphene nitride. The generation was proven by XPS analysis in finding N1S peak in the spectrum. Detail analysis of N1s peak suggested that the major nitrogen species was pyrrolic type. Furthermore, the presence of CO bond proved the oxidation by OH radical. The reaction product had the value of N/C as high as 0.08, which is comparable to reported values for ultrasonic preparation of graphene nitride. The fact indicates that the significance of chemical effects of MHz range ultrasound, and the finding of the simple preparation method will accelerate practical application of graphene nitride.

Effect of torrefaction on the evolution of carbon and nitrogen during chemical looping gasification of rapeseed cake

Chemical looping gasification (CLG) is a novel approach to efficiently convert rapeseed cake (RC) to tunable syngas and NH3. However, the low energy density of RC seriously hinders its utilization. Meanwhile, torrefaction is an effective pretreatment for biomass upgrading. Hence, the combination of torrefaction with CLG is proposed as an alternative technology to efficiently utilize RC. In this work, the effect of torrefaction temperature on the evolution behaviors of carbon and nitrogen in CLG of RC with Ca2Fe2O5 OC was systematically investigated using TG-FTIR. Results show that torrefaction can effectively improve the physiochemical properties of RC. The torrefied RC possesses higher energy density and HHV, and lower atomic H/C and O/C ratios. Additionally, higher torrefaction temperature can facilitate the thermal degradations of N-IN and labile NP, with the productions of NH3 and HCN. During CLG, the rise of OC/Fuel mass ratio can increase the yields of the major gases (CO2, CO, CH4, NH3 and HCN), owing to both the oxidative effect of the lattice oxygen (O*) and the catalytic effects of Fe3+ and Ca2+ in OC. Moreover, torrefaction pretreatment can improve the CLG behavior of RC and the optimal torrefaction temperature is 250 °C, attributing to the improvement of fuel stability after torrefaction. Besides, torrefaction can marginally reduce the yields of the major nitrogen species (NH3 and HCN). This is ascribed to both the more stable structure of heterocyclic-N and the insufficiency of H radical in the torrefied RC compared to the raw. These findings provide a feasible guidance for the effective insight in nitrogen evolution during CLG coupled with torrefaction, and thereafter for the efficient utilization of biomass.

Modeling Soil Nitrate Accumulation and Leaching in Conventional and Conservation Agriculture Cropping Systems

Nitrate is a major groundwater inorganic contaminant that is mainly due to fertilizer leaching. Compost amendment can increase soils’ organic substances and thus promote denitrification in intensively cultivated soils. In this study, two agricultural plots located in the Padana plain (Ferrara, Italy) were monitored and modeled for a period of 2.7 years. One plot was initially amended with 30 t/ha of compost, not tilled, and amended with standard fertilization practices, while the other one was run with standard fertilization and tillage practices. Monitoring was performed continuously via soil water probes (matric potential) and discontinuously via auger core profiles (major nitrogen species) before and after each cropping season. A HYDRUS-1D numerical model was calibrated and validated versus observed matric potential and nitrate, ammonium, and bromide (used as tracers). Model performance was judged satisfactory and the results provided insights on water and nitrogen balances for the two different agricultural practices tested here. While water balance and retention time in the vadose zone were similar in the two plots, nitrate leaching was less pronounced in the plot amended with compost due to a higher denitrification rate. This study provides clear evidence that compost addition and no-tillage (conservation agriculture) can diminish nitrate leaching to groundwater, with respect to standard agricultural practices.

Development and application of a fully integrated model for unsaturated-saturated nitrogen reactive transport

This paper presents a fully integrated model to simulate coupled unsaturated-saturated flow and reactive transport of ammonium and nitrate, the two major nitrogen species. Based on our previous work of developing a coupled model of unsaturated-saturated flow and solute transport of a single species, the key contribution of this study is to develop a new mathematical model and the new computer code for a comprehensive list of biogeochemical reactions, which are necessary for simulating nitrogen reactive transport. The computer code is verified by comparing its simulated results with those obtained using another model for a synthetic case. Model calibration and validation are conducted for two real-world cases to simulate nitrogen reactive transport. The two cases are at the experimental plot scale with the sewage water irrigation and at the field scale with the septic tank effluent infiltration, respectively. Quantitative evaluation of the numerical modeling results indicates that the new model and computer code can accurately simulate field observations of moisture content, water table elevation, and nitrogen concentration. For example, the root mean square error for simulating moisture content can be as small as 0.01. The code is computationally efficient to capture spatial and temporal trends of nitrogen concentrations at the field scale with a large number of computational nodes and time steps. The fully integrated model is a promising tool for large-scale modeling of water flow and nitrogen transformation and transport under complex conditions in agricultural and urban environments.

Evidence of energy levels due to nitrogen dimers in silicon

Nitrogen-and-boron doped Czochralski Si samples are converted into n-type by annealing at 600 °C due to formation of Shallow Thermal Donors (STDs). The temperature dependence of the electron concentration, measured by Hall effect down to the liquid Helium temperature, is not however consistent with existence of only STDs and compensating boron acceptors; there is clearly an extra acceptor species with a level close to the conduction band, and of a concentration comparable to the total concentration of nitrogen. This acceptor centre is thus identified with the major nitrogen species, N 2 and N 2O. These two species can be distinguished by using samples from the seed-end and tail-end of a crystal: the level due to N 2 is about E c −27 meV, and that due to N 2O about E c −33 meV.

Novel Multi‐functional Mixed‐oxide Catalysts for Effective NOx Capture, Decomposition, and Reduction

AbstractIn this paper, novel multi‐functional mixed‐oxide catalysts have been rationally designed and developed for the effective abatement of NOx. CaxCo3 – xAl hydrotalcite‐like compounds (where x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) are first synthesized by co‐precipitation and calcined at 800 °C for 4 h in air to derive the mixed oxides. The resultant mixed oxides are generally of spinel phase, where the CaO phase is segregated when x ≥ 2.5. It has subsequently been found that the derived oxides are catalytically multi‐functional for NOx decomposition, capture, and reduction. For example, the mixed Ca2Co1Al1‐oxide can decompose 55 % NO at 300 °C in 8 % oxygen, completely trap NO for 750 s, and capture 12.88 and 18.06 mg g–1 NO within 30 and 60 min, respectively. The catalytic activities of the Ca2Co1Al1‐oxide catalyst have been further improved by incorporating La to form a quaternary catalyst Ca2Co1La0.1Al0.9‐oxide. This catalyst significantly enhances the NO decomposition to 75 %, extends the complete trapping time to 1100 s, and captures more NO at 300 °C in 8 % O2 (19.02 mg g–1 NO within 60 min). The in‐situ IR spectra of the catalysts with adsorbed NO indicates that the major nitrogen species formed on the catalysts are various kinds of nitrites and nitrates, which can be readily reduced by H2 within 6 min at 350 °C. Therefore, the excellent catalytic activity of layered double hydroxide (LDH)‐based mixed oxides for NO decomposition, storage, and reduction can be achieved by the elegant combination of normal transition metals.

Application of thermal-dissociation laser induced fluorescence (TD-LIF) to measurement of HNO<sub>3</sub>, Σalkyl nitrates, Σperoxy nitrates, and NO<sub>2</sub> fluxes using eddy covariance

Abstract. Nitrogen exchange between the atmosphere and biosphere directly influences atmospheric composition. While much is known about mechanisms of NO and N2O emissions, instrumentation for the study of mechanisms contributing to exchange of other major nitrogen species is quite limited. Here we describe the application of a new technique, thermal dissociation-laser induced fluorescence (TD-LIF), to eddy covariance measurements of the fluxes of NO2, total peroxy acyl and peroxy nitrates, total alkyl and multifunctional alkyl nitrates, and nitric acid. The technique offers the potential for investigating mechanisms of exchange of these species at the canopy scale over timescales from days to years. Examples of flux measurements at a ponderosa pine plantation in the mid-elevation Sierra Nevada Mountains in California are reported and used to evaluate instrument performance.

An intercomparison of airborne PAN measurements

As part of the NASA Tropospheric Chemistry Program a series of field intercomparisons have been initiated to evaluate state‐of‐the‐art capability for measuring key tropospheric species. These intercomparisons, designated as Chemical Instrumentation Test and Evaluation (CITE), are conducted as part of NASA's Global Tropospheric Experiment. The objectives of the second series of instrument tests, CITE 2, were to evaluate instrumentation for measuring NO2, HNO3, and peroxyacetyl nitrate (PAN) and to determine for various tropospheric environments the relative abundances and partitioning among the major nitrogen species. This paper summarizes the results from the PAN instrument intercomparisons. Other results are addressed in companion papers. Both PAN instruments use the same detection principle of electron capture gas chromatography of a cryogenically enriched sample of ambient air. NASA Ames Research Center and the National Center for Atmospheric Research were responsible for the respective instruments. The intercomparisons included three exchanges of standards and 13 intercomparison flights in which a variety of types of air masses were sampled. Nine flights were based from Ames Research Center, California, and the remaining four were ferry flights between Ames and Wallops Flight Center, Virginia (aircraft home base). Flight altitudes ranged from 150 to 5000 m above ground level. All flights but one were during daylight hours. PAN mixing ratios during the flight intercomparison periods were generally <300 parts per trillion by volume (pptv), and about 40% of the results for mixing ratios were <100 pptv. At mixing ratios of <100 pptv the two instruments agreed on the average to about 17 pptv with a 95% confidence interval of ±9 pptv. Instrument agreement at PAN levels of 100–300 pptv was of the order of 25% with a confidence interval of ±6%. These levels of agreement are within expected limits based on the stated accuracy and precision of the two instruments. However, it is noted that for some of the individual intercomparison data periods, agreement was outside expected levels.