Wet Nitrogen Research Articles

Impact of Atmosphere on Recovered Carbon Fibers From Poly Ether Ether Ketone (PEEK) Based Composites During Thermoconversion

Carbon Fibers Reinforced Polymer composites (CFRP) are high added value materials used in many manufactured products. Especially in aeronautics, thermosetting resins tend to be replaced by heat-resistant thermoplastic polymers. The aim of the work is to evaluate suitable operating conditions of thermoconversion for the recovery of carbon fibers from Poly Ether Ether Ketone (PEEK)/carbon fibers composites. Micro and pilot scale tests have been performed in nitrogen, wet nitrogen, air, and wet air. Thermogravimetric analysis of PEEK/carbon fiber composites showed a moderate decomposition onset temperature of the composite at 515 °C and 510 °C in dry nitrogen and dry air respectively. The oxidative atmosphere did not significantly impact this temperature since the first mass loss was not atmosphere dependent. However, after the first PEEK degradation reaction, the nature of the atmosphere appeared as a great issue. Total mass loss was significantly improved with temperature (full oxidation of polymer and carbon fibers up to 800 °C) and with reaction time using air. Indeed, at pilot scale, the matrix was fully degraded in air atmosphere at 550 °C for 1 h while only 42% and 46% was reached in nitrogen and steam/nitrogen respectively. Comparison of thermogravimetric data between wet and dry atmospheres revealed that steam plays a thermal retardant role leading to some differences on the matrix degradation and on the surface morphology of the carbon fiber at pilot scale. Air treatments at pilot scale induced a reduction of fiber diameters (< − 3.7%) but the tensile strengths of recovered carbon fibers were preserved with an average retention of mechanical properties of 81%-85%. It has been concluded that recycling of PEEK/carbon composite required an oxidant to split up carbon fibers from the PEEK matrix.

Dominant contribution of nitrogen compounds in precipitation chemistry in the Lake Victoria catchment (East Africa)

This work provides a complete chemical characterization of rains collected in the tropical rural site of Mbita (Kenya) on the shores of Lake Victoria (annual rainfall 1259.3 mm). We present a wet nitrogen deposition budget including inorganic and organic dissolved nitrogen in relation with atmospheric sources of gases and particles, precipitation rate and air mass transport. A unique 2 yr monitoring data set (2017–2019), providing 183 rain samples was collected and analyzed according to international standards (WMO/GAW). Considering that precipitation represents the largest contributor of water to the Lake Victoria (80%), this study gives new insights in the seasonality of nutrients wet deposition (WD) inputs in the unique natural resource represented by Lake Victoria and its catchment. Four main contributions to the chemical composition of precipitation, were identified: (a) a 28% terrigenous contribution related to crustal and biomass sources, (b) a 14% marine contribution related to Indian ocean air masses intrusion, (c) a 15% organic contribution due to volatile organic carbon emissions from biomass burning and vegetation and (d) a predominant nitrogenous contribution of 39% due to livestock and fertilizers, biomass burning and neighboring agricultural fires. Ammonium and nitrate volume weighed mean concentrations are 36.75 and 8.88 μeq l−1, respectively. Rain in Mbita is alkaline (pH = 5.8) highlighting neutralization by heterogeneous chemistry. Total nitrogen WD is 8.54 kgN ha−1 yr−1, 58 760 tN yr−1 for the entire lake, with 26% attributed to dissolved organic nitrogen. A total atmospheric deposition of 15 kgN ha−1 yr−1 is estimated taking into account dry deposition estimate from literature, showing that the Lake Victoria ecosystem is exposed to eutrophication. An extensive and regular monitoring of wet and dry nitrogen deposition is highly recommended both in-shore and off-shore to help improving the efficiency of nitrogen use in agricultural areas and reduce nitrogen losses around Lake Victoria.

Chemical Modification of B4C Films and B4C/Pd Layers Stored in Different Environments.

B4C/Pd multilayers with small d-spacing can easily degrade in the air, and the exact degradation process is not clear. In this work, we studied the chemical modification of B4C films and B4C/Pd double layers stored in four different environments: a dry nitrogen environment, the atmosphere, a dry oxygen-rich environment, and a wet nitrogen environment. The XANES spectra of the B4C/Pd layers placed in a dry oxygen-rich environment showed the most significant decrease in the σ* states of the B–C bonds and an increase in the π* states of the B–O bonds compared with the other samples. X-ray photoelectron spectroscopy (XPS) measurements of the samples placed in a dry oxygen-rich environment showed more intensive B-O binding signals in the B4C/Pd layers than in the single B4C film. The results of the Fourier-transform infrared spectroscopy (FTIR) showed a similar decrease in the B–C bonds and an increase in the B–O bonds in the B4C/Pd layers in contrast to the single B4C film placed in a dry oxygen-rich environment. We concluded that the combination of palladium catalysis and the high content of oxygen in the environment promoted the oxidization of boron, deteriorated the B4C composition.

Long-term application of manure reduced nutrient leaching under heavy N deposition

Little is known about the importance of long-term fertilization in crop production and nutrient leaching under heavy wet nitrogen (N) deposition from the atmosphere (WNDA) in tropical and subtropical soils. Thus, a 15-year (2004–2018) field experiment was established on a yellow soil (Orthic Arisols) near Zunyi, Southwest China, to compare the effects of fertilization on maize yields and nutrient leaching in a rotation system of summer maize-winter wheat-summer flue-cured tobacco (or sometimes sweet potato). All crops in this system received no fertilizers (CK), only chemical fertilizers (CF), or manure plus chemical fertilizers (MCF). MCF achieved higher yield and economic efficiency of fertilizers than CF after the first four maize cropping seasons. These results suggested a positive interaction between manure and chemical fertilizers. Maize plants used residual nutrients in the soil from the previous fertilizer management, which may interfere with manure efficiency. MCF alleviated soil acidification and increased soil organic matter (OM), available nutrients, microbial biomass, and enzyme activities (urease and phosphatase compared with CK and invertase and catalase compared with CF). The stimulation of microbial growth and activities may lead to OM depletion in the CF soil, while OM added into the soil in the MCF treatment may exceed microbial OM consumption. During the maize growing season, MCF decreased N and K leaching losses compared with CF. WNDA accounted for 10–12% of N fertilized to maize and 32–69% of maize N uptake in the unfertilized soil. WNDA may thus be an important N source of maize in N-poor soils.

Long-term atmospheric inorganic nitrogen deposition in West African savanna over 16 year period (Lamto, Côte d’Ivoire)

We present a long term assessment trend of atmospheric inorganic nitrogen deposition in Sub Saharan Africa (2000–2015) using observational and model data. This work proposes a compilation of International Network to study Deposition and Atmospheric chemistry in Africa wet and dry nitrogen deposition fluxes collected at the wet savanna site of Lamto (Côte d’Ivoire). Total deposition calculation takes in account: (a) gaseous (NO2, NH3, HNO3) dry deposition fluxes estimated by considering nitrogen compound concentrations at the monthly scale and modeling average monthly dry deposition velocities, (b) particulate PM10 (pNO3 −, pNH4 +) dry deposition fluxes calculated using the same inferential method and (c) wet deposition (WD) fluxes including ions concentration measurements (NO3 −, NH4 +) in rainwater combined with rainfall amount. We demonstrate for the first time the monthly and annual decreasing trends for dry nitrogen deposition of N-NO2 (−2.33% month−1 and −2.54% yr−1) and N-NH3 (−2.55% month−1 and −2.89% yr−1), but increasing trends for dry deposition of N-HNO3 (+1.00% month−1) and WD of N-NO3 − (+1.67% month−1 and +2.13% yr−1) and N-NH4 + (+2.33% month−1 and +3.36% yr−1). Dry season N-NO2 deposition flux decline shows agreement with long term trend in NOx emissions by biomass burning. Increasing trends for wet N deposition signals a gradual increase of nitrogen fertilizers use in agricultural practices in the Lamto area. Results also show no significant trend in total N deposition over the 16 year study period explained by the compensation of decreasing and increasing trends for dry and wet N deposition, respectively. However, at the annual scale, the mean total N deposition flux is estimated to 10.3 ± 1.2 kgN ha−1 yr−1 over the 16 year period, indicating an increase of 8% compared to the period 2000–2007.

Structural, thermal stability and electrical conductivity of zirconium substituted barium cerate ceramics

Barium cerate perovskite ceramics substituted with zirconium BaCe1-xZrxO3 (x = 0, 0.05, 0.10, 0.15, 0.20) were prepared by the standard solid-state reaction route. The x-ray diffraction patterns affirmed the single-phase orthorhombic symmetry of the synthesized ceramics. The thermal stability of the samples has been checked by thermogravimetric analysis (TGA). TGA of dry and pre-hydrated (pH2O (g) ≈ 0.03 atm and 1.0 atm) compositions revealed that all the samples are stable up to a temperature of 800 °C. However, the samples treated at a higher partial pressure of water are found less stable. The crystalline phase of the studied compositions before and after TGA was measured with the Raman study, confirming that most of the parent phases exist or remain stable even after the treatment of samples at higher vapor pressure. Thermal stability gradually improved with increasing Zr-substitution. The TGA results that are consistent with the Raman studies proved the sample with x = 0.20 is the most stable among the studied compositions. Complex impedance spectroscopy studies clearly demonstrated the impact of bulk and grain boundary on the total resistance of the compounds with different zirconium contents. The Arrhenius dependence of the total conductivity indicates that the conductivity decreased with an increase in Zr concentration both in air and wet nitrogen atmosphere. Comparing the conductivity under both ambiances suggests that some additional charged species participate in the conduction mechanism under the wet environment. These are ascribed to the protonic defects, developing into barium cerate via extrinsic oxygen vacancies because of high-temperature sintering.

Wet Inorganic Nitrogen Deposition at the Daheitin Reservoir in North China: Temporal Variation, Sources, and Biomass Burning Influences

Atmospheric nitrogen deposition is of great concern to both air quality and the ecosystem, particularly in northern China, which covers one-quarter of China’s cultivated land and has many heavily air polluted cities. To understand the characteristics of wet N deposition at rural sites in northern China, one-year wet deposition samples were collected in the Daheitin reservoir region. Due to the intense emissions of gaseous nitrogen compounds from heating activities during cold seasons and distinct dilution effects under different rainfall intensities and frequencies, the volume weighted mean concentrations of wet N deposition showed higher levels in dry seasons but lower levels in wet seasons. In contrast, the wet N deposition rates varied consistently with precipitation, i.e., high during the wet season and lower during the dry season. The annual wet deposition rate of total inorganic ions (the sum of NO3−–N and NH4+–N) at the rural site in North China from July 2019 to June 2020 was observed at 18.9 kg N ha−1 yr−1, still remained at a relatively high level. In addition, biomass burning activities are ubiquitous in China, especially in northern China; however, studies on its impact on wet N deposition are limited. Non-sea salt potassium ion (nss-K+) was employed as a molecular tracer to investigate the characteristics of biomass burning activities as well as their impact on the chemical properties of wet N deposition. Three precipitation events with high nss-K+ levels were captured during the harvest season (June to July). The variations in the patterns of nss-K+, deposited N species, and ratios of nss-K+ to nitrogen species as well as their relationships all indicated that biomass burning emissions contributed remarkably to NO3−–N but had a minor influence on NH4+–N.

Economizing on Precious Metals in Three‐Way Catalysts: Thermally Stable and Highly Active Single‐Atom Rhodium on Ceria for NO Abatement under Dry and Industrially Relevant Conditions**

AbstractWe show for the first time that atomically dispersed Rh cations on ceria, prepared by a high‐temperature atom‐trapping synthesis, are the active species for the (CO+NO) reaction. This provides a direct link with the organometallic homogeneous RhI complexes capable of catalyzing the dry (CO+NO) reaction. The thermally stable Rh cations in 0.1 wt % Rh1/CeO2 achieve full NO conversion with a turn‐over‐frequency (TOF) of around 330 h−1 per Rh atom at 120 °C. Under dry conditions, the main product above 100 °C is N2 with N2O being the minor product. The presence of water promotes low‐temperature activity of 0.1 wt % Rh1/CeO2. In the wet stream, ammonia and nitrogen are the main products above 120 °C. The uniformity of Rh ions on the support, allows us to detect the intermediates of (CO+NO) reaction via IR measurements on Rh cations on zeolite and ceria. We also show that NH3 formation correlates with the water gas shift (WGS) activity of the material and detect the formation of Rh hydride species spectroscopically.

Economizing on Precious Metals in Three-Way Catalysts: Thermally Stable and Highly Active Single-Atom Rhodium on Ceria for NO Abatement under Dry and Industrially Relevant Conditions*.

We show for the first time that atomically dispersed Rh cations on ceria, prepared by a high-temperature atom-trapping synthesis, are the active species for the (CO+NO) reaction. This provides a direct link with the organometallic homogeneous RhI complexes capable of catalyzing the dry (CO+NO) reaction. The thermally stable Rh cations in 0.1 wt % Rh1 /CeO2 achieve full NO conversion with a turn-over-frequency (TOF) of around 330 h-1 per Rh atom at 120 °C. Under dry conditions, the main product above 100 °C is N2 with N2 O being the minor product. The presence of water promotes low-temperature activity of 0.1 wt % Rh1 /CeO2 . In the wet stream, ammonia and nitrogen are the main products above 120 °C. The uniformity of Rh ions on the support, allows us to detect the intermediates of (CO+NO) reaction via IR measurements on Rh cations on zeolite and ceria. We also show that NH3 formation correlates with the water gas shift (WGS) activity of the material and detect the formation of Rh hydride species spectroscopically.

Electrical Conductivity of Y&lt;sup&gt;3+&lt;/sup&gt; Doped Ba(Ce,Zr)O&lt;sub&gt;3&lt;/sub&gt; in Wet N&lt;sub&gt;2&lt;/sub&gt; Atmosphere Prepared with the Addition of Brij-97

Y-doped barium cerate-zirconate ceramic oxide is proven to be a competent material as an electrolyte with high proton conductivity as well as chemical and mechanical stabilities in carbon dioxide and water vapour atmospheres. This ceramic oxide requires high processing temperature which will results in the increase of particle/grain size. Hence, modification on the synthesis route has been studied in reducing the particle/grain size of the ceramic by lowering the calcination temperature. In this work, BaCe0.54Zr0.36Y0.1O2.95 (BCZY) powder was synthesized with addition of surfactant (Brij-97) through an established modified sol-gel route. Single BCZY perovskite phase was successfully obtained at calcination temperature of 950°C which was lower than our previous study (T=1100°C). The prepared sample was made into pellet by a dry pressing technique with diameter, d=13 mm and thickness, t~2 mm and then subjected to a two-step sintering method prior to morphological and electrical measurements. Impedance measurement was carried out at intermediate temperatures (500-800°C) using an Electrochemical Impedance Spectroscopy (EIS) in wet nitrogen atmosphere. Impedance spectrum was analysed to obtain the behaviour of grain core and grain boundary responses by a fitting procedure using a brick-layer model. Scanning electron microscope (SEM) analysis of fractured pellet revealed that BCZY prepared with the assisted of Brij-97 exhibited dense, homogenous and less agglomerate grain with grain size around 88 nm, which may explain the enhancement in the total conductivity of the BCZY electrolyte.

Wet season nitrogen export from a residential stormwater pond.

Stormwater runoff is recognized as a cause of water quality degradation because it may carry nitrogen (N) and other pollutants to aquatic ecosystems. Stormwater ponds are a stormwater control measure often used to manage stormwater runoff by holding a permanent pool of water, which reduces the peak flow, magnitude of runoff volume, and concentrations of nutrients and pollutants. We instrumented the outlet of a stormwater pond in an urban residential neighbourhood in Florida, United States to (1) investigate the concentration and composition of N forms during the summer rainy season (May to September 2016), and (2) determine the bioavailability of organic N in the stormwater pond with a bioassay experiment. A total of 144 outflow water samples over 13 storm events were collected at the outlet of the stormwater pond that collects runoff from the residential catchment. Samples were analysed for various inorganic N [ammonium (NH4–N), nitrate (NO3–N)], and organic N forms [dissolved organic nitrogen (DON), and particulate organic nitrogen (PON)]. Flow-weighted mean concentration of total N (TN) in pond outflow for all collected storm events was 1.3±1.42 mg L-1, with DON as the dominant form (78%), followed by PON and NO3–N (each at 8%), and NH4–N (6%). In the bioassay experiment, organic N (DON+PON) was significantly decreased by 25–28% after 5 days of incubation, suggesting that a portion of the DON carried from the pond outflow to receiving water bodies may be bioavailable. These results suggest that efforts to mitigate stormwater N outflows from urban ponds should incorporate both inorganic and organic N in management plans.

Wet and Dry Nitrogen Depositions in the Pearl River Delta, South China: Observations at Three Typical Sites With an Emphasis on Water‐Soluble Organic Nitrogen

AbstractInorganic nitrogen (N) deposition in China is among the highest in the world, yet organic N deposition in the country has not been well constrained. In this study, wet and dry depositions of both organic and inorganic N were observed for 2 years at three contrasting sites (urban‐rural‐forest) in the Pearl River Delta (PRD) region, South China. Determined annual total dissolved N (TDN) deposition rates were 39.8, 33.8, and 52.0 kg N ha−1 year−1 at the urban, rural, and forest sites, respectively. The contributions of NO3−‐N, NH4+‐N, and water‐soluble organic N (WSON) to total N deposition were 26.7–37.8%, 34.6–40.9%, and 26.1‐32.3%, respectively. Wet N deposition accounted for about 54–68% in total N deposition at the sites. It is worth noting that the deposition rates of WSON in the PRD were among the highest in developed regions in the world. In wet depositions, the concentrations and proportions of WSON were significantly higher during the harvest seasons, especially at the non‐urban sites, mainly due to enhanced biomass burning in the period. In dry deposition, the seasonal pattern of WSON was inconsistent with that of NO3−‐N or NH4+‐N. Biological/soil organic N might be the important sources of WSON in dry deposition. Our results suggest that WSON contributed significantly to atmospheric N deposition in the PRD and more attentions should be paid to the WSON to get a true picture of N depositions and its impacts on the ecosystem.

Experimental investigations on performance of TiN and TiAlN coated tools in cryogenic milling of AISI D2 hardened steel

A new cryogenic cooling approach implemented in Liquid Nitrogen as a lubricant has been developed for cutting zone during our milling operation in AISI D2 hardened steel, to enhance the metal removing operation efficiency. In our work, the test investigation has taken place in an estimated efficiency of TiN as well as TiAlN layered tools during dry, wet and liquid Nitrogen during lubrication techniques. The applications for the LN2 coolant proved in thus minimization for the temperature behind cutting, cutting forces, finishing off the surface for both the tools, compared with those measured in dry and wet metal removing operational situations. It is observed that while machining with TiAlN coated tool, the temperature behind cutting was minimized nearly up to 18% and the forces behind the cutting were minimized approximately 13% compared to machining with a TiN coated tool under LN2 cooling condition.

Effects of wet atmospheric nitrogen deposition on epiphytic lichens in the subtropical forests of Central China: Evaluation of the lichen food supply and quality of two endangered primates.

Over the last few decades, the threat posed to biodiversity and ecosystem function by atmospheric nitrogen (N) deposition has been increasingly recognized. The disturbed nutrient balance and species composition of plants induced by higher N deposition can impact the biodiversity of the organisms that consume the plants. In this research, we implemented several experiments to estimate the effects of increased N deposition on the growth, survival, and nutrients of the dominant epiphytic lichens in the subtropical mountains in Central China to assess the lichen food amount and nutritional quality for two endangered primates endemic to China. Our results indicated that the thallus growth and propagule survival of the lichens were significantly decreased when nitrogen addition changed from 6.25 to 50.0kgN·ha-1·y-1; it was also shown that lichen biomass could be decreased by 11.2%-70.2% when the deposition addition exceeded 6.25kgN·ha-1·y-1. Further, our study revealed that increased nitrogen deposition also reduced the nutritional quality of the lichens via reducing the soluble protein and soluble sugar levels and increasing the fiber content, which would substantially affect the diet selection of the plants consumers in the region, particularly the populations of the two lichen-eating endangered primate species, Rhinopithecus roxellana and R. bieti. Our experimental study suggested that the nitrogen pollution derived from anthropogenic activities could cause cascading effects for the whole forest ecosystem of Central China; thus, more studies about nitrogen deposition in this region are required.

Characteristics, sources and environmental implications of atmospheric wet nitrogen and sulfur deposition in Yangtze River Delta

Nitrogen (N) and sulfur (S) deposition rates have changed rapidly in China during recent years. But few studies have simultaneously measured wet N and S deposition rates on different land use types in the same region. In present study, 238 precipitation samples were collected between May 2016 and April 2017 using wet-only auto-samplers, and the wet N and S deposition rates were measured at three sites with different land use types (urban, agriculture, and lake) in the Yangtze River Delta (YRD), Eastern China. The annual wet deposition rates of total N (TN), ammonium (NH4+), nitrate (NO3−), dissolved organic N (DON), water-insoluble particulate N (WIPN), and sulfate (SO42−) were 16.87–26.64, 6.38–10.81, 5.92–11.11, 1.43–1.96, 2.23–2.67, and 9.07–22.53 kg N (S) ha−1 yr−1, respectively. The wet N and S deposition rates were in the order: agriculture > urban > lake sites, and the seasonal variations in wet N and S deposition were similar at all sites. DON and WIPN contributed 6.4–11.8% and 10.7–16.2% of the total wet N deposition, respectively. Chemical N fertilization and fossil fuel were important sources of wet N and S deposition. Annual wet N and S deposition are important nutrient sources that stimulate the eutrophication and soil/water acidification in the YRD. To minimize the environmental cost of wet N and S deposition in the YRD, it is critical to investigate the sources of N and S.

C/g-C3N4 hybrid nanosheets obtained by gaseous stripping to boost photocatalytic hydrogen evolution performance

Graphitic carbon nitride (g-C3N4) is a new generation metal-free polymer semiconductor photocatalyst for solar water splitting. In this work, we report a gaseous treatment in wet nitrogen ambience, which can realize carbon deposition and nanosheets stripping in one step. The free carbon functions as electron trapping and the bridge of g-C3N4 and co-catalyst Pt, producing a high charge separation efficiency. The carbon content in the C/g-C3N4 hybrid nanosheets can be adjusted by changing ethanol content in the treating ambience. The optimized C/g-C3N4 (5%) nanosheets achieve the highest hydrogen evolution rate of 10482.62 μmol h−1 g−1, which is 2.3 times that of g-C3N4 (0%) nanosheets, even 13.9 times that of bulk g-C3N4. Optical properties, charges transfer and specific surface area of the C/g-C3N4 hybrid nanosheets are measured to discuss the mechanism of photocatalytic hydrogen evolution. The combination of high optical absorption in visible region and high charge separation efficiency contribute to the enhanced hydrogen evolution performance.

Aluminum dual doping and oxygen transport pathway in novel Sr11Mo4−xAlxO23 oxide-ion solid electrolytes

Three new electrolytes of composition Sr11Mo4-xAlxO23-δ (x = 0.5, 1.0 and 1.5) were synthesized by wet-chemistry procedures (citrate method) as polycrystalline samples. They were crystallographically studied from synchrotron and neutron diffraction techniques. They derive from the Sr11Mo4O23 complex perovskite, which can be rewritten as Sr1.75□0.25SrMoO5.75, highlighting the relationship with double perovskites A2B′B″O6. From these analyses via Rietveld refinement, a dual doping was found from synchrotron data, where the aluminum is equally allocated at both Sr (B′) and Mo (B″) sites. A detailed analysis of the neutron data from Difference Fourier Maps (DFM) unveiled the oxygen delocalization around the Mo site. From the refined crystal structures at room and high temperatures, a Bond Valence Sum Map (BVSM) analysis was useful to find the oxygen pathway in the crystal structure, and the minimum density to allow connections among oxygen atoms. The structural characterization was complemented with thermogravimetric and thermodilatometric analysis. The ionic conductivity was measured from electrochemical impedance spectroscopy (EIS) in wet and dry air and nitrogen atmospheres.

Improvement of Surface Passivation of Tunnel Oxide Passivated Contact Structure by Thermal Annealing in Mixture of Water Vapor and Nitrogen Environment

The effects of post‐crystallization annealing within various atmospheres on the surface passivation quality of tunnel oxide passivated contact (TOPCon) for crystalline silicon (c‐Si) solar cells are studied. The results provide an innovative method for improving the surface passivation of the as‐crystallized TOPCon structure by annealing at moderate temperatures ranging from 300 to 700 °C within a mixture of water vapor and nitrogen atmosphere. The wet nitrogen improves the implied open‐circuit voltages (iVoc) from 700–710 to ≈730 mV on average and reduces the single‐side reverse saturated recombination current density (J0) to 3.8 fA cm−2, which is much more effective than the so‐called forming‐gas annealing. In addition, the contact resistivity remains in low values of ≈5 mΩ cm2, ensuring its application in the high‐efficiency c‐Si solar cell. Secondary ion mass spectroscopy provides the evidence that the enhanced surface passivation by the water vapor annealing results from the hydrogen incorporation, which is logically believed to passivate the defects in the oxide and c‐Si interface region. This study proposes a simple and cost‐effective technique to improve the surface passivation of TOPCon structure, which is suitable for the high‐efficiency c‐Si solar‐cell manufacture.

Long-term trends of wet inorganic nitrogen deposition in Rocky Mountain National Park: Influence of missing data imputation methods and associated uncertainty

Excess reactive nitrogen (Nr) deposition is occurring in Rocky Mountain National Park and impacting sensitive ecosystems. In 2006, the National Park Service, State of Colorado, and Environmental Protection Agency established the goal to reduce Nr deposition to below the ecosystem critical load by 2032. Progress is tracked using 5-year averages of annual wet inorganic nitrogen (IN) deposition measured at Loch Vale, Colorado, by the National Atmospheric Deposition Program (NADP). This remote high alpine site is challenging to operate, and large fractions of the annual precipitation, at times >40%, had invalid IN concentrations. Annual wet IN deposition is calculated using the NADP protocol, which replaces missing concentrations with the annual precipitation-weighted mean (PWM) concentration of valid samples. This protocol does not account for seasonal variations in IN concentrations and the inverse relationship between concentration and precipitation amounts. Invalid samples occurred more frequently in the winter and at high and low precipitation amounts, and the NADP protocol generally overestimated annual deposition rates, by as much as 20%. Here, a new method for imputing missing weekly IN concentrations that accounts for their seasonal and precipitation dependence is introduced. Using a bootstrapping analysis shows that the new method reduced the errors in the annual deposition rates by about 30% compared to the NADP protocol and the biases were near zero. The overall trend in the wet IN deposition rates was found to be flat from 1990 to 2017, but the nitrate contribution decreased about 33%, which was offset by a nearly equal increase in ammonium wet deposition. These trends are consistent with known changes in nitrate and ammonium precursor emissions. The long-term trends in the annual IN deposition rates were similar using both data imputation methods, but the 2013–2017 average was about 10% smaller using the new method.

Stabilization of atmospheric nitrogen deposition in China over the past decade

Increasing atmospheric nitrogen deposition can influence food production, environmental quality and climate change from the regional to global scales. As the largest developing country, China is expected to experience a rapid increase in N deposition. However, the lack of information on dry N deposition limits our understanding of the historical trend of the total N deposition, as well as the main drivers of this trend. Here, we use extensive datasets that include both wet and dry N deposition to evaluate the spatiotemporal variation of N deposition and the changes of its components in China during 1980–2015. Three significant transitions in N deposition in China were observed. First, the total N deposition began to stabilize in 2001–2005, mostly due to a decline in wet NH4+ deposition. Subsequently, a shift to approximately equal wet and dry N deposition occurred in 2011–2015, accompanied by increasing dry deposition. Finally, the contribution of reduced N components in the deposition decreased due to increasing NO3− deposition. These transitions were jointly driven by changes in the socioeconomic structure in China and vigorous controls in N pollution. The three observed important transitions challenge the traditional views about the continuous increase in N deposition in China. Nitrogen deposition in China has been almost constant over the past decade, as decreasing wet deposition has balanced increasing dry deposition, according to analyses of extensive datasets on wet and dry nitrogen depositions in China.