High HNO3 Concentrations Research Articles

Precise target capture and the dynamic separation of Sn(IV) in highly acidic media by combining N and P donor covalent organic framework silica-based composite adsorbents

A silica-based adsorbent (P507@COF-TpAzo/SiO2) with nitrogen and phosphorus donors was prepared for industrial separation and recovery of Sn(IV) by in-situ growth of covalent organic framework (COF) on a silica substrate combined with vacuum impregnation. The materials were tested and analyzed by the scanning electron microscope (SEM), X-ray diffraction (XRD) and other characterization techniques, which demonstrated that the adsorbent has an enormous specific surface area, excellent heat resistance, and a regular morphological structure. The static experimental results showed that the adsorbent displayed remarkable selectivity for Sn(IV) in high HCl and HNO3 concentration environments, with excellent kinetics (∼60 min) and outstanding adsorption capacities (60.02 mg/g in 3 M HCl, 92.59 mg/g in 3 M HNO3) in different media at 3 M acidity. Cycle performance testing demonstrated that the adsorbent exhibited excellent stability (cycle times ≥8). Analysis using Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) showed that the synergistic adsorption results of N and P were reflected, mainly by the synergistic complexation of P=O and N=N-C. The potential sites for the adsorption of the adsorbent towards Sn(IV) were predicted by density functional theory (DFT) calculations, and the adsorbent demonstrated a more stable binding energy with Sn(IV). Finally, dynamic separation and efficient enrichment (>210) of Sn(IV) in highly acidic wastewater were realized by designing a penetrating column separation process. P507@COF-TpAzo/SiO2 satisfied the requirements of the dynamic adsorption experiments, bridging the research gap of dynamic separation, and provides a new strategy for the industrial removal and recovery of Sn(IV), as well as a way for environmental protection and industrial green production.

Influence of plutonium content in dissolver solutions derived from irradiated fast reactor fuels on plutonium stripping in multistage countercurrent liquid–liquid extraction with acid split flowsheet

ABSTRACT In the acid split flowsheet, the Pu content in the dissolver solution of nuclear fuel has a significant impact on the configuration of flowsheet and the Pu content in the products. The influence of Pu content in dissolver solutions of nuclear fuel on the Pu stripping has been studied. The decontamination performance of Cs as major fission products was assessed, and Cs was decontaminated well in the acid split flowsheet. High HNO3 concentration in the feed solution and at the co-decontamination section was adjusted for the co-recovery of Np with U and Pu, contributing to Np oxidation and the increase in the distribution ratio of Np. The experimental results demonstrate that the Pu content in the U/Pu and U products increased with an increase in the Pu content in the feed solution. The calculated results indicate that the Pu leakage into the U product is suppressed with the Pu stripping solution only at low temperature under our experimental conditions, and Pu is recovered into the U/Pu product efficiently. This study proves that the Pu leakage into the U product is controlled and the acid split flowsheet is flexible with change in the Pu content in the feed solution.

Study of Cellulose Extraction from Robusta Coffee Husk Using NaOH Solution

This study reports on manufacturing cellulose from robusta coffee husks through a solid-liquid extraction process. A high yield of cellulose can be achieved by extraction using 3.5% HNO3 at a temperature of 100 oC with a gain of 35.4%. Meanwhile, the extraction process with 4.5% HNO3 at a temperature of 80 oC only achieved a yield of 32.8%. From the results of this study, it can be seen that the smaller the concentration of HNO3 used and the higher the temperature, the greater the yield of cellulose produced. The X-ray diffraction pattern shows high peaks appearing at an angle of 2θ around 22.5o; this area is a typical peak of the cellulose structure. High crystallinity was obtained at a concentration of 3.5% HNO3 at a temperature of 100 oC at 82.47%, while the lowest crystallinity was found at a 5.5% HNO3 concentration at a temperature of 100 oC at 74.27%. The decrease in crystallinity was caused by the high temperature and concentration of HNO3, which caused the acid to penetrate quickly into the cellulose tissue layer and hydrolyze the crystalline regions of cellulose. FT-IR analysis showed a high absorption area at 3314 cm-1 and a low absorption area at 1028 cm-1, typical of Robusta coffee husk cellulose. The absorption located around the 3314 cm-1 bands is a stretch of the –OH group and the absorption in the 1028 cm-1 band is related to the -CH2 group. SEM can show the morphology of cellulose with smaller and uniform crystal dimensions with a scale of 20 µm.

Effect of water molecules co-intercalation and hydrolysis on the electrochemical deconsolidation of matrix graphite in aqueous nitric acid

Separation of complete TRISO-coated fuel particles from matrix graphite is challenging but important for the post-irradiation examination (PIE) of high-temperature gas-cooled reactor (HTGR) fuel elements. Electrochemical technology is considered one of the most promising and effective approaches in this regard. Herein, to explore the influence of HNO3 concentration on galvanostatic deconsolidation, 4%–68% HNO3 were taken as examples. The matrix graphite anodes gradually exfoliated to fragments in 34% HNO3, while expanding in other concentrations. The characterization results of deconsolidated fragments and galvanostatic curves identified the highest oxygen content was reached in 34% HNO3 due to the combined effect of intercalation, hydrolysis and oxygen evolution. In higher HNO3 concentrations like 68%, the intercalating agent predominates and therefore the intercalation and following hydrolysis reactions are the main causes of matrix graphite deconsolidation, with no oxygen evolution occurring. In contrast, in lower HNO3 concentrations like 4%, the violent oxygen evolution reaction hinders the intercalation and hydrolysis reactions. In short, only the combined interaction of intercalation, hydrolysis and oxygen evolution can deconsolidate the bulk matrix graphite into a more homogeneous powder. This work will provide more insights into the electrochemical deconsolidation mechanism and process of both HTGR fuel elements and other graphite materials.

Electrochemical Oscillation during Dissolution of Iron in High Concentration of Nitric Acid

Electrochemical oscillations are attractive phenomena from the viewpoint of dynamic self-organization of molecular systems. In general, an N-shaped negative differential resistance (N-NDR) plays a crucial role in the appearance of oscillations because it gives rise to oscillatory instability [1]. Most of the oscillations can be classified into an N-NDR type or “hidden” N-NDR (HN-NDR) type oscillator. The former shows current oscillations under potential controlled conditions and hysteresis loops under current-controlled conditions, whereas the latter shows not only current oscillations but also potential oscillations.Iron dissolves in aqueous HNO3 solutions, accompanied by hydrogen evolution reaction. This dissolution reaction is written as follows:Fe → Fe2+ + 2e- (1)2H+ + 2e- → H2. (2)On the other hand, the dissolution does not take place in concentrated HNO3 solutions (i.e., 13 M HNO3) because of the formation of a passivation film on the surface. However, when the concentration of HNO3 is approximately 10 M, the dissolution and passivation of iron occur alternatively. In other words, only when an iron wire is immersed in a high concentration of HNO3, the rest potential of the iron wire oscillates spontaneously. This phenomenon is of interest because its appearance does not require any external devices.In this work, to clarify the mechanism of the spontaneous oscillation, we observe the surface of an iron wire during the oscillation using a high-speed camera (Figure 1) and measure electrochemical impedance spectra. From these studies, we can say that the oscillation is an HN-NDR type, which will be discussed in the presentation. Reference M. Orlik, Self-Organization in Electrochemical Systems I, Springer-Verlag Berlin Heidelberg, Berlin (2012). FIGURE CAPTION Figure 1 Time course of rest potential of an iron electrode in 10 M nitric acid and snapshots of the electrode. Figure 1

Nitric acid dry deposition associated with equilibrium shift of ammonium nitrate above a forest by long-term measurement using relaxed eddy accumulation

The dry deposition process of nitrogen compounds still has considerable uncertainty due to the complex compound behavior in the atmosphere. To enhance understanding of the nitric acid (HNO3) dry deposition process that largely contributes to the total nitrogen deposition, we associate this process with the equilibrium shift of ammonium nitrate (NH4NO3) to HNO3 and ammonia (NH3) near the surface. We obtained the flux of HNO3 and PM2.5 components above a forest in suburban Tokyo using a relaxed eddy accumulation (REA) system incorporating the denuder/filter-pack sampling technique. We conducted continuous samplings on a weekly basis over a long-term period, from October 14, 2016 to October 3, 2018, including leafy and leafless conditions. The measured deposition velocities of fine NO3− particles were significantly (p < 0.05) larger than those of fine SO42− particles and similar to those of HNO3, regardless of the leafy and leafless periods. The larger deposition velocities of fine NO3− particles caused by the equilibrium shift of NH4NO3 were found to be similar to previous measurements at the same site. The measured deposition velocities of HNO3 were low and included many emission cases compared to those of fine NO3− particles. The lower HNO3 deposition velocities were associated with the equilibrium shift of NH4NO3 to the gas phase, causing the suppressed deposition and apparent emission of HNO3, particularly during the leafless period. The emission of HNO3 is possibly due to high HNO3 concentration near the surface, which is attributed to a small removal of the leafless canopy. The turbulence enhanced both the upward and downward fluxes of HNO3. These results will contribute to the better understanding for the dynamics of the nitrogen compounds in the atmosphere and the accurate assessment for the nitrogen deposition.

Highly Sensitive Porous PDMS-Based Capacitive Pressure Sensors Fabricated on Fabric Platform for Wearable Applications.

A novel porous polydimethylsiloxane (PDMS)-based capacitive pressure sensor was fabricated by optimizing the dielectric layer porosity for wide-range pressure sensing applications in the sports field. The pressure sensor consists of a porous PDMS dielectric layer and two fabric-based conductive electrodes. The porous PDMS dielectric layer was fabricated by introducing nitric acid (HNO3) into a mixture of PDMS and sodium hydrogen bicarbonate (NaHCO3) to facilitate the liberation of carbon dioxide (CO2) gas, which induces the creation of porous microstructures within the PDMS dielectric layer. Nine different pressure sensors (PS1, PS2,..., PS9) were fabricated in which the porosity (pore size, thickness) and dielectric constant of the PDMS dielectric layers were varied by changing the curing temperature, the mixing proportions of the HNO3/PDMS concentration, and the PDMS mixing ratio. The response of the fabricated pressure sensors was investigated for the applied pressures ranging from 0 to 1000 kPa. A relative capacitance change of ∼100, ∼323, and ∼485% was obtained by increasing the curing temperature from 110 to 140 to 170 °C, respectively. Similarly, a relative capacitance change of ∼170, ∼282, and ∼323% was obtained by increasing the HNO3/PDMS concentration from 10 to 15 to 20%, respectively. In addition, a relative capacitance change of ∼94, ∼323, and ∼460% was obtained by increasing the PDMS elastomer base/curing agent ratio from 5:1 to 10:1 to 15:1, respectively. PS9 exhibited the highest sensitivity over a wide pressure sensing range (low-pressure ranges (<50 Pa), 0.3 kPa-1; high-pressure ranges (0.2-1 MPa), 3.2 MPa-1). From the results, it was observed that the pressure sensors with dielectric layers prepared at relatively higher curing temperatures, higher HNO3 concentrations, and higher PDMS ratios resulted in increased porosity and provided the highest sensitivity. As an application demonstrator, a wearable fit cap was developed using an array of 16 pressure sensors for measuring and mapping the applied pressures on a player's head while wearing a helmet. The pressure mapping aids in observing and understanding the proper fit of the helmet in sports applications.

Modeling of the Competition between Uranyl Nitrate and Nitric Acid upon Extraction with Tri-n-butyl Phosphate.

Uranium is a strategic element and plays an important role in energy resources. A H2O–HNO3–UO2(NO3)2–TBP (tri-n-butyl phosphate)–diluent system is commonly used for uranium separation and purification in liquid–liquid extraction. Uranyl nitrate is promoted by the existence of nitrate at low HNO3 concentrations but is inhibited at high HNO3 concentrations. Considering the competitive extraction between HNO3 and UO2(NO3)2, a generic extraction model is developed. The activities of components in the aqueous phase were estimated using Pitzer models. The thermodynamic equilibrium constants and Pitzer parameters were regressed by experimental data. The resulting model was able to successfully predict uranyl nitrate, nitric acid, and water extraction over a large range of conditions (U, 0–1.8 mol/L; HNO3, 0–10 mol/L; TBP, 5–100 vol %) within average absolute relative deviations of 11.2, 15.7, and 23.8%, respectively. The predicted results show that water and nitric acid were extracted as di-solvates HNO3·(TBP)2·H2O and (TBP)2·2H2O at low nitric acid concentrations, with the formation of mono-solvates HNO3·TBP and HNO3·TBP·H2O as the acid concentration increased. Uranyl nitrate was shown to be rejected from the organic phase as the formation of HNO3·TBP and HNO3·TBP·H2O in acid was extracted at high acid concentrations.

Degradation of sulfamethazine by cerium mediated photoelectrochemical oxidation with hydroxyl radical oxidation effect

A cerium (Ce) mediated photoelectrochemical oxidation (MPEO)/H2O2 system, integrating UV photocatalysis and hydroxyl radical (⋅OH) oxidation, was developed to improve the degradation of sulfamethazine (SMT). SMT is an emerging contaminant with medical toxicity in environmental matrices. In the study of electrolytic production of Ce(IV), the Ce(III)/Ce(IV) redox reaction was found to have good reversibility at high HNO3 concentrations above 0.5 M, due to more cerium ions being trapped by NO3- ions near the anode. In addition, optimum current density of 8 mA cm−2 and reaction temperature of 313 K, for Ce(IV) production, are determined by considering specific energy consumption (SEC) and Ce(IV) percent yield. The MPEO/H2O2 system demonstrates favorable SMT removal efficiencies of 76% and 98%, at treatment times of 60 and 120 min, respectively. This system outperforms the mediated electrochemical oxidation (MEO) and MPEO systems, for SMT degradation. In addition, the kinetics of SMT degradation, using the MPEO/H2O2 system, was found to follow a proposed pseudo-first order model, rather than a pseudo-second order model, and exhibit a higher rate constant than those of the MEO and MPEO systems. Moreover, the concentration of ⋅OH during SMT treatment can be estimated by measuring the concentrations of 4-Hydroxybenzoic acid (4-HBA) and 3,4-Dihydroxybenzoic acid (3,4-DHBA), over time. Our findings reveal that introducing UV irradiation and H2O2 into the MEO system can induce a higher production of ⋅OH in addition to the Ce(IV) ions, thus leading to improved SMT removal efficiency.

Does addition of 1-octanol as a phase modifier provide radical scavenging radioprotection for N,N,N',N'-tetraoctyldiglycolamide (TODGA)?

To mitigate third phase formation in next generation used nuclear fuel reprocessing technologies, the addition of 1-octanol has been trialed. However, contradictory reports on the radiolytic effect of 1-octanol incorporation on separation ligand degradation need to be resolved. Here, 50 mM N,N,N',N'-tetraoctyldiglycolamide (TODGA) dissolved in n-dodecane was gamma irradiated in the presence and absence of 1-octanol (2.5-10 vol%) and a 3.0 M HNO3 aqueous phase. Radiation-induced TODGA degradation exhibited pseudo-first-order decay kinetics as a function of absorbed gamma dose for all investigated solution and solvent system formulations. The addition of 1-octanol afforded diametrically different effects on the rate of TODGA degradation depending on solvent system formulation. For organic-only irradiations, 1-octanol promoted TODGA degradation (d = 0.0057 kGy-1 for zero 1-octanol present vs.∼0.0073 kGy-1 for 7.5-10 vol%) attributed to a favourable hydrogen atom abstraction reaction free energy (-0.31 eV) and the ability of 1-octanol to access a higher yield of n-dodecane radical cation (RH˙+) at sub-nanosecond timescales. This was rationalized by determination of the rate coefficient (k) for the reaction of 1-octanol with RH˙+, k = (1.23 ± 0.07) × 1010 M-1 s-1. In contrast, irradiation in the presence of 1-octanol and a 3.0 M HNO3 aqueous phase afforded significant radioprotection (d = 0.0054 kGy-1 for zero 1-octanol present vs.≤ 0.0044 kGy-1 for >2.5 vol%) that increases with 1-octanol concentration, relative to the single phase, organic-only solutions. This effect was attributed to the extraction of sufficiently high concentrations of HNO3 and H2O into the organic phase by TODGA and 1-octanol as adducts which interfere with the hydrogen atom abstraction process between the 1-octanol radical and TODGA. Our findings suggest that the addition of 1-octanol as a phase modifier will enhance the radiation robustness of TODGA-based separation technologies under envisioned solvent system conditions in the presence of aqueous HNO3.

Recovery of neodymium and praseodymium from nitrate-based leachate of permanent magnet by solvent extraction with trioctylphosphine oxide

For recovery of the rare earth elements neodymium and praseodymium from end-life permanent magnets, solvent extraction experiments were carried out on the nitrate-based leachate with trioctylphosphine oxide (TOPO) as an extractant. TOPO selectively extracted Nd and Pr in preference to Fe at higher HNO3 concentration. Nd and Pr extracted into TOPO were selectively stripped using HCl solution, and the small amount of co-loaded Fe was stripped with ammonium oxalate solution after removal of Nd and Pr. McCabe-Thiele diagrams for the extraction and stripping of Nd/Pr were constructed. The results were validated in counter-current simulation experiments using real leachate solution. Finally, a process for recovering Nd and Pr from the nitric acid leachate of permanent magnets was proposed.

Trends and seasonal variability of atmospheric NO2 and HNO3 concentrations across three major African biomes inferred from long-term series of ground-based and satellite measurements

In the framework of the INDAAF (International Network to study Deposition and Atmospheric chemistry in AFrica) programme, part of the ACTRIS European Research Infrastructure for the long-term observation of Aerosols, Cloud, and Trace gases, this paper aims to study trends and seasonal variability of surface atmospheric NO2 and HNO3 concentrations, and OMI (Ozone Monitoring Instrument) NO2 over 6 sites in tropical Africa. Sites are located in west and central Africa to represent the major African biomes: dry savanna (Banizoumbou, Niger and Katibougou, Mali), wet savanna (Djougou, Benin and Lamto, Côte d’Ivoire) and forest (Bomassa, Republic of Congo and Zoétélé, Cameroon). Ground-based NO2 and HNO3 concentrations were obtained over the period 1998–2015 using INDAAF passive samplers at a monthly basis, and NO2 Vertical Column Densities (VCDs) from OMI for a 1° grid cell around each sites were obtained from 2005 to 2015. Mean annual NO2 concentrations ranged from 2.3 ± 1.2 to 0.9 ± 0.4 ppb from dry savannas to forests, representing a north south gradient. In dry savannas, we observe two concentration peaks of NO2 appearing at the beginning and the end of the wet season both for ground-based and satellite measurements, whereas at wet savannas and forest sites, NO2 concentrations are highest in the dry season. The seasonality of surface NO2 observations provide further evidence for a large role of microbial soil NOx emissions in dry savannas and of biomass burning NOx emissions in wet savanna and forest sites. Mean annual HNO3 concentrations ranged from 0.4 to 0.5 ppb in dry and wet savannas to 0.2–0.3 ppb in forest. In dry ecosystems, higher HNO3 concentrations are measured in the early wet season, consistent with NO2 results. The analysis of a long-term dataset of surface O3 concentrations indicates that HNO3 production can mainly be explained by the photooxidation of NOx. Mann-Kendall and Seasonal Kendall statistical tests showed that NO2 surface concentrations have a significant decreasing seasonal and annual trends at multiple sites (p-value < 0.05) ranging from −2.96% yr−1 (at Zoétélé) to −0.64% yr−1 (at Banizoumbou). HNO3 results indicate no trends except at Bomassa (1.07% yr−1). The decreasing NO2 ground-based concentration trends observed in wet savannas sites are correlated with OMI NO2 decreasing trends at these sites. Trends obtained for NO2 concentrations in wet savanna and forest ecosystems are consistent with trends of NOₓ biomass burning emissions.

Preparation and characterization of tri-n-octylamine microcapsule (TOA-MC) used for selective separation of Re(VII) [chemical analogs of Tc(VII)] in the high level liquid radioactive waste (HLLW)

TOA-MC was developed to act as absorbent for selective separation of 99Tc(VII) from high-level radioactive liquid waste. The uptake (%) of Re(VII) a substitute for Tc(VII) due to similar chemical behavior by TOA-MC normally exceeding 95% in the presence of dilute HNO3 was strongly retained and decreased with higher HNO3 concentration by batch method. The surface morphology, thermal stability and diameter/size distribution of the microcapsules were examined by scanning electron microscopy, thermogravimetric analysis and digital microscope, respectively. The chemical structure was characterized using Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy.

The effect of powder preparation method on the artificial photosynthesis activities of neodymium doped titania powders

The effects of nanostructure on the artificial photosynthesis activities of undoped and Nd doped titania (TiO2) powders prepared by three different chemical co-precipitation methods were investigated. Substitutional/interstitial N and S doping was observed in powders due to the presence of high concentrations of HNO3 (NP) and H2SO4 (SP) in the powder preparation media, respectively. Nd, N and S doping caused anatase/rutile phase transformation inhibition and crystallite size reduction in the nanostructure. Light absorption was significantly enhanced by Nd doping and the residual SO42−/NOx species in the nanostructure. Photocatalytic hydrogen production activity of Nd doped NP powder was 4 times greater than undoped NP powder at 700 °C and had a high purity (CO:H2 ratio∼0.00). CO was determined to be the main product in photocatalytic CO2 reduction. NP powders had the highest CO yields and Nd doping enhanced CO production. The powders with high crystallite sizes and rutile weight fractions had the highest artificial photosynthesis activities.

Photoluminescence, morphological and electrical properties of porous silicon formulated with different HNO3 concentrations

Abstract In this study, porous silicon (PS) with observable luminescence was fabricated on p-type Si (1 0 0) substrate by wet chemical etching with the mixture of HF and different HNO3 concentrations in the ratio of 1:100. The porosity of PS shows dependent on HNO3 concentration. SEM images exhibit the average pore size increases with the increasing of HNO3 concentration. The emission of PS was characterized by photoluminescence (PL) spectroscopy. The PS is able to emit orange-red visible PL under UV illumination with the peak falls within the wavelength region of (620–660) nm. Brighter emission is observed on PS etched at higher HNO3 concentration, and the emission peak shifts to shorter wavelength when the energy gap and surface roughness increase. The calculated band gaps are lied in the range of (1.90–2.00) eV, which is higher than Si. Moreover, the surface conductivity decreases as the PS energy gap increases.

Adsorption recovery of Pd(II) from aqueous solutions by persimmon residual based bio-sorbent

A low cost bio-sorbent, named “PPF resin”, was prepared by immobilizing persimmon residual with formaldehyde and it was characterized before and after adsorption of Pd(II). The adsorption behavior of PPF resin towards Pd(II) from aqueous solutions was studied by batch and column adsorption methods. The adsorption equilibrium of Pd(II) on PPF resin was achieved within 840min, and the experimental data were well fitted with the pseudo-second-order rate model. Higher initial concentration and adsorption temperature led to higher equilibrium adsorption amount, and the adsorption isotherms could be well described by Langmuir model. The column studies suggested that the resin was effective for the adsorption of Pd(II) from aqueous solutions, and the loaded Pd(II) could be easily desorbed by acidic thiourea solution. The adsorption process of Pd(II) on PPF resin might be the multiple reactions of electrostatic interaction and reductive adsorption, in which Pd(II) was reduced to Pd(0) as confirmed by the XRD pattern of PPF resin after adsorption of Pd(II). The resin exhibited outstanding selective adsorption towards Pd(II) from actual leach liquor of waste PCBs at a high concentration of HNO3. The results suggested that the PPF resin can be used as an active bio-sorbent for the recovery of Pd(II) from aqueous environment.

Cracking of n-hexane over hierarchical MOR zeolites derived from natural minerals

Cost-effective and efficient catalysts for pyrolysis and catalytic cracking can be derived from low-cost and abundantly available natural minerals. Herein, we report the fabrication of hierarchical mordenite (MOR) zeolites with an enhancement in micropore properties, which were obtained by ion exchange followed by dealumination of natural zeolites. Crystallinity, textural properties and morphologies of the hierarchical catalysts were characterized by using X-ray diffraction (XRD), nitrogen physisorption and field-emission scanning electron microscopy (SEM). The XRD patterns show that the parent minerals contain natural mordenite as the dominant phase (73–83 wt%). The severity of the dealumination was studied by applying different concentrations of nitric acid (HNO3). Dealumination affected crystallinity, Si/Al ratio, mesoporosity of mordenite, and selectivity of products in n-hexane cracking. Crystallinity of hierarchical MOR decreased with higher HNO3 concentrations. High selectivity to propylene with propylene/ethylene ratio of 1.26 was achieved over mordenite treated with mild dealumination by HNO3 (1 M). These cost-effective catalysts derived from natural zeolites are potentially applied in chemical industries.

Pollution Properties of Water-Soluble Secondary Inorganic Ions in Atmospheric PM2.5 in the Pearl River Delta Region

ABSTRACTBased on the online observation of PM2.5 mass concentration, its water-soluble inorganic ions, and their gaseous precursors during August of 2013 to March of 2014 at the atmospheric supersite in the Pearl River Delta (PRD) region, the inter-action of the secondary compositions and their precursors was discussed, and the pollution properties of the secondary inorganic ions were revealed. During the whole measurement period, the average concentrations of SO42–, NO3– and NH4+ were 16.6 µg m–3, 9.0 µg m–3 and 10.2 µg m–3, respectively, with total contribution to PM2.5 of 55.8%, indicating the significant role of secondary transformation in PM2.5 pollution. The seasonal average total contributions of SO42–, NO3– and NH4+ to PM2.5 varied from 46.0% to 64.3%, lowest in summer and highest in winter. The contributions of SO42– and NH4+ to PM2.5 were relatively stable; while those of NO3– in different seasons were distinct, even dominating PM2.5 in some pollution cases in winter. NH3 was abundant with an annual average concentration of 15.2 µg m–3, facilitating the neutralization of H2SO4 and HNO3 with the average [NH4+]/(2[SO42–] + [NO3–]) equivalent charge ratio of 1.1. The maximum daily peak concentration of HNO3 was as high as 18.6 µg m–3, providing an evidence for the strong oxidizing property of the atmosphere in the PRD region. The theoretical equilibrium constant (Ke) of NH4NO3 is always lower than the observed concentration product (Km = [NH3] × [HNO3]) in spring and winter with higher HNO3 concentrations; while in over 60% of the time during summer and autumn, mainly during daytime, Ke was higher. In general, the strong oxidizing property and NH3 played important roles in the fine particle pollution in the PRD region.

Variation in isotopologues of atmospheric nitric acid in passively collected samples along an air pollution gradient in southern California

The sources and oxidation pathways of atmospheric nitric acid (HNO3) can be evaluated using the isotopic signatures of oxygen (O) and nitrogen (N). This study evaluated the ability of Nylasorb nylon filters to passively collect unbiased isotopologues of atmospheric HNO3 under controlled and field conditions. Filters contained in passive samplers were exposed in continuous stirred tank reactors (CSTRs) at high (16 μg/m3) and moderate (8 μg/m3) HNO3 concentrations during 1–4 week deployment times. Filters were concurrently exposed at high and low N deposition sites along a gradient in the Sonoran Desert. Filters deployed in CSTRs at moderate HNO3 concentrations for 1–2 weeks had greater variation of δ18O relative to the 3–4 week deployments, while high concentration samples were consistent across weeks. All deployment means were within 2‰ of the source solution. The δ15N of all weekly samples were within 0.5‰ of the source solution. Thus, when deployed for longer than 3 weeks, Nylasorb filters collected an isotopically unbiased sample of atmospheric HNO3. The initial HNO3 samples at the high deposition field sites had higher δ15N and δ18O values than the low deposition sites, suggesting either two independent sources of HNO3 were mixing or that heavier isotopologues of HNO3 were preferentially lost from the gas phase through physical deposition or equilibrium chemical reactions. Subsequent HNO3 samples were subject to summer monsoon conditions leading to variation of isotopic signatures of N and O following 2-source mixing dynamics. Both sites mixed with a source that dominated during the two discrete precipitation events. The high number of lightning strikes near the samplers during the monsoon events suggested that lightning-created HNO3 was one of the dominant mixing sources with an approximate isotopic signature of 21.6‰ and −0.6‰ for δ18O and δ15N respectively. Two-source mixing models suggest that lightning-created HNO3 made up between 40 and 42% of atmospheric HNO3 at the high deposition sites and 59–63% at the low deposition during the 4 week exposure.

The transport of atmospheric NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; and HNO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; over Cape Town

Abstract. Cape Town, the most popular tourist city in Africa, usually experiences air pollution with unpleasant odour in winter. Previous studies have associated the pollution with local emission of pollutants within the city. The present study examines the transport of atmospheric pollutants (NOx and HNO3) over South Africa and shows how the transport of pollutants from the Mpumalanga Highveld, a major South African industrial area, may contribute to the pollution in Cape Town. The study analysed observation data (2001–2008) from the Cape Town air-quality network and simulation data (2001–2004) from a regional climate model (RegCM) over southern Africa. The simulation accounts for the influence of complex topography, atmospheric conditions, and atmospheric chemistry on emission and transport of pollutants over southern Africa. Flux budget analysis was used to examine whether Cape Town is a source or sink for NOx and HNO3 during the extreme pollution events. The results show that extreme pollution events in Cape Town are associated with the lower level (surface – 850 hPa) transport of NOx from the Mpumalanga Highveld to Cape Town, and with a tongue of high concentration of HNO3 that extends from the Mpumalanga Highveld to Cape Town along the south coast of South Africa. The prevailing atmospheric conditions during the extreme pollution events feature an upper-level (700 hPa) anticyclone over South Africa and a lower-level col over Cape Town. The anticyclone induces a strong subsidence motion, which prevents vertical mixing of the pollutants and caps high concentration of pollutants close to the surface as they are transported from the Mpumalanga Highveld toward Cape Town. The col accumulates the pollutants over the city. This study shows that Cape Town can be a sink for the NOx and HNO3 during extreme pollution events and suggests that the accumulation of pollutants transported from other areas (e.g. the Mpumalanga Highveld) may contribute to the air pollution in Cape Town.