Nitrogen Discharge Research Articles

Influence of pulsed gas injections on the stability of Townsend dielectric barrier discharges in nitrogen at atmospheric pressure

This work investigates the effects of pulsed nitrogen gas injections on the stability of Townsend dielectric barrier discharges operated in continuous nitrogen gas flows at atmospheric pressure. For single-pulse injections with pulse durations lower than the continuous gas residence time (∼50 ms), current–voltage characteristics reveal homogeneous discharges with a single current peak per half-cycle of the applied voltage. However, a sudden decrease of the discharge power over time combined with a temporary transition from homogeneous to filamentary discharge is observed for longer pulses at fixed pulsed gas flows and for higher pulsed gas flows at fixed pulse duration. In addition, for multiple pulsed gas injections with repetition frequencies between 0.1 and 10 Hz, discharge destabilisation increases with the number of pulses. Time-resolved optical emission spectroscopy reveals that, over the single pulse time scale, temporal variations of the emission intensities are longer than the expected residence times of the continuous and pulsed gas flows. Furthermore, a rise of oxygen impurities can be seen over both single and multiple-pulses time scales. Two-dimensional gas flow simulations reveal that pulsed injections introduce sharp and narrow temporal gas velocity profiles over the range of experimental conditions investigated, with no cumulative effects in the discharge cell from one pulse to the other. However, pulsed operation introduces significant changes in the neutral gas composition with time scales comparable to those revealed by electrical and optical diagnostics. In such conditions, the outgassing of impurities adsorbed on surfaces located upstream of the discharge cell plays a vital role in Townsend discharges’ physics and characteristics.

A Fixed-Film Bio-Media Process Used for Biological Nitrogen Removal from Sewage Treatment Plant

In this study, a lab-scale fixed-film bio-media process was developed and operated to evaluate nitrogen removal from domestic sewage treatment plants. For nitrogen removal, the fixed-film bio-media process was applied in series with anaerobic, anoxic, and aerobic units in three separate reactors that were operated continuously at the same loading rates and hydraulic retention time. A biofilm separation bioreactor was developed for on-site domestic wastewater treatment and the bioreactor employed synthetic fiber modules so that the biomass could be completely attached to the media. In this paper, the performance of the fixed-film bio-media process with an average flow rate was evaluated before and after stabilization of the treatment system for nitrogen removal. The results show that the fixed-film bio-media process was successful for improved nitrogen removal from secondary and tertiary treated wastewater, with a 77% decrease in the total nitrogen discharge. Rapid nitrification could be achieved, and denitrification was performed in the anoxic filter with external carbon supplements during tertiary treated sewage wastewater. However, aeration was supplied after the stabilization process to achieve the nitrification and denitrification reaction for nitrogen removal. However, stable aeration supply could enhance nitrification at moderate temperature with benefits from complete retention of nitrifying bacteria within the system due to bio-media separation.

Surface-Active Plasma-Polymerized Nanoparticles for Multifunctional Diagnostic, Targeting, and Therapeutic Probes

Surface-functionalized polymeric nanoparticles have advanced the field of nanomedicine as promising constructs for targeted delivery of molecular cargo as well as diagnostics and therapeutics. Conventionally, the functionalization of polymeric nanoparticles incorporates tedious wet chemical methods that require complex, multistep protocols. Surface-active plasma-polymerized nanoparticles (PPNs) produced by a dry, low-pressure plasma process can be easily functionalized with multiple ligands in a simple step. However, plasma polymerization remains limited by the challenge of efficient collection of PPNs from low-pressure plasma reactors. Here, we demonstrate a simple method to overcome this limitation by delaying the inflow of the polymer-forming precursor gas, acetylene, into a nitrogen and argon plasma discharge. We provide evidence that this cutting-edge development in the plasma polymerization method drastically enhances the collection yield of nanoparticles by 2.5-fold, compared to the simultaneous inflow of the gases. COMSOL Multiphysics simulations support our experimental data and provide insights into the role of pressure gradients in regulating the forces controlling the collection of the particles. Surface characterization data revealed that changing the sequence of the precursor gas inflow had no significant effect on the physicochemical properties of the nanoparticles, as critically important for theranostic applications. A model, green fluorescent protein, was successfully conjugated to the surface of the PPNs via a reagent-free, one-step incubation process that immobilized the biomolecule while retaining its biological activity. Cytotoxicity of the particles was assessed by a lactate dehydrogenase (LDH) assay at concentrations of up to 5 × 105 nanoparticles per cell. Despite their high concentrations, the nanoparticles were remarkably well tolerated by the cells, demonstrating their superb potential for in vivo cellular uptake. This study advances previous research on plasma-polymerized nanoparticles, introducing a low-waste synthesis method that achieves higher yields. This sustainable technology has important implications for the production of multifunctional nanoparticles for drug delivery, tumor targeting, and medical imaging.

Evaluation of extruded full-fat soybean as the substitution for fish meal in diets for juvenile Scophthalmus maximus based on growth performance, intestinal microbiota, and aquaculture water quality

Extrusion technology is applied to improve the utilization of soy products, providing an alternative to fish meal (FM) as a component of feed. In this study, a 60-day feeding of turbot (Scophthalmus maximus) was conducted to evaluate the effects of the partial substitution of FM with extruded full-fat soybean (EFS) on growth performance, digestion capacities, intestinal microbiota, and aquaculture water quality. Four isonitrogenous (427.95 ± 0.38 g/kg crude protein) and isolipidic (9.80 ± 1.13 g/kg crude lipid) diets were formulated to contain FM with EFS substitution of 0% (EFS 0%), 10% (EFS 10%), 20% (EFS 20%), and 30% (EFS 30%). Each diet was fed twice a day in triplicate to juvenile turbot (initial body weight, 5.35 ± 0.07 g). The results showed that the turbot fed with EFS 30% had significantly lower body weight, specific growth rate, and protein efficiency ratio than turbot with other diets. In addition, the EFS 30% significantly decreased total serum cholesterol, low-density lipoprotein contents, intestinal folds height, and apparent digestibility coefficients of dry matter and crude protein. It also increased pathogenic Cyanobacteria at the phylum level, decreased probiotics, Rhodobacterales, and Pseudomonadales at the order level, and decreased leuconostoc and Psychrobacter at the genus level. Compared with other treatments, the EFS 30% displayed the lowest proportion of nitrogen for growth and the highest fecal nitrogen loss. Furthermore, the water quality indicators such as ammonia nitrogen discharge, total suspended solids, and fine solid accumulation (< 15 μm) reached the peak in the EFS 30% group. In conclusion, EFS is a feasible turbot feed that can substitute up to 20% of FM with no adverse effects on growth performance, digestive function, intestinal microbiota, and aquaculture water quality.

On electric field measurements based on intensity ratio of 1 − and 2 + systems of nitrogen in discharges with high specific deposited energy

Analysis of optical emission spectroscopy (OES) in application to the measurements of the electric field has been performed for the nanosecond capillary discharge in molecular nitrogen at moderate gas pressure at high specific energy deposition. Significant discrepancy between results of electric field measurements by OES technique and capacitive probe measurements is demonstrated. Decay rates of excited species as well as rotation structure of corresponding optical transitions are used to identify possible population/depopulation channels of the () and N2(C3Π u ) states. Kinetic calculations taking into account additional quenching of the () and N2(C3Π u ) states by electrons, additional population of () by electron impact from the ground state of the molecular ion and by a reaction of excited N2() with the ground state of describes adequately behavior of experimentally measured emission of both considered systems.

Atmospheric pressure Townsend discharge in pure nitrogen—a test case for N2() kinetics under low E/N conditions

This work investigates the kinetics of the N2() state in the atmospheric-pressure Townsend discharge (APTD) operated in a barrier discharge setup in pure nitrogen. To understand the complex nature of the N2() state we have developed a detailed state-to-state vibrational kinetic model of N2 applicable mainly at low reduced electric fields (200 Td). The kinetic model benefits from the determination of the electric field and the electron density profile using the equivalent electric circuit analysis. The knowledge of both parameters significantly reduces the number of free parameters of the model and thus improves the accuracy of kinetic predictions. The results of the kinetic model are compared with the measured emission spectra of the second positive system and the Herman infrared system of N2. The use of the sensitivity analysis method leads to a better understanding of the role of specific elementary processes in the APTD mechanism and also to the determination of the density of the two lowest vibrational levels of N2(), which varies between 1012 and 1014 cm−3 depending on the applied voltage. The determination is important, because the two lowest vibrational levels of N2() are considered to play an important role in the secondary emission of electrons from dielectric surfaces. This work shows that the complex state-to-state kinetic modeling in combination with the phase-resolved emission spectroscopy is the key to a better understanding of the processes responsible for establishing and sustaining the APTD mechanism in nitrogen.

Re-hydrolysis characteristics of alkaline fermentation liquid from waste activated sludge: Feasibility as a carbon source for nitrogen removal

To overcome the issue of substandard nitrogen and phosphorus discharge, resulting from the low carbon/nitrogen (C/N) ratio of municipal wastewater, immobilized filler was used to re-hydrolyze the alkaline fermentation liquid of waste activate sludge (WAS) as a nitrogen removing carbon source. The complex organic matter was further hydrolyzed and its denitrification efficiency as a carbon source for nitrogen removal was improved. Volatile fatty acids increased from 1605 ± 5 mg/L to 2546 ± 37 mg/L after re-hydrolysis of mixed-alkali sludge fermentation liquid, and complex organic matter, such as fulvic acids, humic acids, class I aromatic proteins, and soluble microbial products were hydrolyzed into small-molecule organics. When the re-hydrolysis fermentation liquid (RH-SFL) was used as the carbon source for nitrogen removal, the nitrogen removal effect was close to sodium acetate and the nitrogen removal rate (NRR) was up to 98.5 ± 0.5%. According to the NOX--N removal curve, the reaction rate of RH-SFL was significantly higher than before re-hydrolysis (nRH-SFL) (0.486 > 0.38). This technology can significantly improve the effective organic quality in the alkaline fermentation liquid of WAS, which can be more easily utilized by denitrifying bacteria. This provides a feasible and effective solution for nitrogen removal in municipal wastewater with insufficient carbon.

Influence of Pulse Amplitude and Frequency on Plasma Properties of a Pulsed Low-Current High-Voltage Discharge Operated at Atmospheric Pressure

Non-equilibrium conditions in plasma are often achieved by pulsed power delivery, where the pulse shape and repetition rate determine the properties of the plasma constituents and thus its chemical reactivity. The evaluation of the latter is becoming increasingly important to understand the observed effects, especially when new application fields are targeted. The composition of the plasma and the occurring chemical reactions can be calculated using various models. Thereby, the temperature of the electrons, the electron number density, as well as the heavy particle temperature are usually required as the basis of such calculations. In this work, the influence of pulse amplitude and repetition rate on these plasma parameters is determined by laser scattering for a low-current, high-voltage discharge operated with nitrogen at atmospheric pressure. In particular, the characteristic parameters regarding the plasma free electrons in such discharges have not yet been experimentally determined to this extent. The results are validated by spectroscopic measurements, i.e., the electron density is estimated from the Stark broadening of the hydrogen beta line and the heavy particle temperature is estimated by fitting the spectrum of nitrogen molecular transitions. Depending on the operating frequency, a pure nitrogen discharge with an input power of about 650 W displays an electron density between 1.7×1021m−3 and 2.0×1021m−3 with electron temperatures in the range of 40,000 K and heavy particle temperatures of about 6000 K in the core of the discharge channel. Furthermore, a relatively slow electron recombination rate in the range of 20 µs is observed.

Effect identification and analysis of tailwater on sediment denitrifier abundances and denitrification in an urban wetland

Excessive anthropogenic nitrogen discharges have led to increasing nitrogen in aquatic systems, resulting in eutrophication problems. To address this problem, urban wetlands are used to remove nitrogen from wastewater treatment plant tailwater because of their efficient nitrogen removal capabilities. At the same time, high‑nitrogen tailwater can exert numerous impacts on the sediment denitrifier communities and denitrification of urban wetlands, and it is necessary to clarify this impact. In this research, we investigated denitrifier (nirK-, nirS- and nosZ-denitrifier) abundances and potential denitrification rate of 30 sediment samples from two urban wetland rivers in Haizhu National Wetland Park (China). One river called experimental river (ER) receives tailwater from a wastewater treatment plant, and the other called control river (CR) is unaffected by the tailwater. Moreover, we also determined the environmental variables to distinguish their relative effects on the variance of denitrifier abundances and denitrification rate in the two rivers. The results showed that the water quality was significantly different between ER and CR, while sediment property was not significant (p < 0.05). And it is unable to distinguish which has the greater denitrification rate between ER and CR. The redundancy analysis and path analysis indicated that riverine nutrient concentrations (e.g., ambient carbon and nitrogen) and physicochemical parameters (e.g., ambient temperature, dissolved oxygen and pH) were important determinants for denitrifier abundances and denitrification in ER and in CR, respectively. Furthermore, denitrifier abundances had an insignificant impact on denitrification in ER, but a considerable impact on denitrification in CR. The findings of this research can help to further understand how the tailwater affects sediment denitrifier communities and denitrification in urban wetland rivers, and to make better use of urban wetlands as a natural purification method.

Nutrient recovery from wastewater in India: A perspective from mass and energy balance for a sustainable circular economy

Limited phosphorus availability and increased eutrophication (due to discharge of nitrogen) have pushed everyone to rethink, on how to recover these nutrients. Wastewater (WW) is a potential source to recover N, and P, whereas, in India, it is scarcely explored. In this work, four different nutrient recovery methods were compared from a mass- and energy-balance perspective to understand the overall process flow. From 1000-m3 WW, chemical precipitation yielded 33.8 kg struvite, while micro-algae resulted in 299.1 kg (dry powder). Energy consumption was lowest for the fuel cells at 216.2 kWh/1000 m3, while microalgae used the highest energy at 943.3 kWh/1000 m3. Nonetheless, the cost-saving analysis showed that microalgae (78.6$/1000 m3) as a nutrient recovery choice, had higher savings than any other methods compared. For a country like India, where the two-thirds of urban wastewater is untreated, wastewater-biorefinery options such as nutrient recovery hold the key to a sustainable circular economy.

Implementation of a single-shot LIF technique for 2-D imaging of metastable nitrogen molecules in a discharge afterglow at sub-atmospheric pressures

The nonequilibrium kinetics of nitrogen metastable N2 (A3Σu+) manifold is of a high interest for the non-thermal plasma diagnostics. A review of laser induced fluorescence (LIF) diagnostic techniques of N2 (A3Σu+) metastable molecules in nitrogen discharges indicates the need to introduce single-shot LIF measurements. The main obstacle in introducing the single-shot technique is the extremely weak fluorescence of N2 (A3Σu+) species, which monitoring requires a very sensitive and fast detector. In this paper, 2-D imaging technique of metastable nitrogen molecules in a nitrogen discharge via single-shot LIF is presented. The experiments involved a sub-atmospheric pressure nitrogen afterglow of a positive-pulsed streamer discharge that was generated in a modified wire-to-plate electrode system. Using 2-D single-shot LIF technique, instantaneous images of the spatial and temporal distributions of the metastable N2 (A3Σu+, v”=2) species and streamer optical emission in the nitrogen afterglow were captured for the first time. The LIF from N2 (A3Σu+, v”=2) metastable molecules and the streamer emission from the excited nitrogen molecules had similar spatial distribution. The key factors for successful single-shot LIF measurements were the intensive streamers produced by the modified wire-to-plate electrode system with a short gap distance, and the use of an intensified charge-coupled detector (ICCD) camera equipped with a two-stage microchannel plate (MCP). The single-shot LIF measurement has the advantages of offering the instantaneous distribution of N2 (A3Σu+) species in the discharge, short measuring time, and better spatial resolution. All of this enable a deeper insight into the nonequilibrium kinetics of nitrogen discharges, making the single-shot LIF technique a powerful diagnostic tool, especially when the LIF signal is weak in stochastic discharges.

Administrative responsibility and land-sea synergistic regulating indicators for nutrient pollution: Linking terrigenous emission to water quality target in Laizhou Bay, China

Globally, many bays have been subjected to water quality (WQ) deterioration, due to excessive discharge of terrigenous total nitrogen (TN). In China, several projects have been implemented to control TN loads; however, due to the lack of linkage between a bay’s polluted segments and its basin’s jurisdictions, the WQ improvement efficiency usually is lower than expected. In this study, we focus on the basin of Laizhou Bay (LZB), China. A series of differentiated TN reduction indicators for 13 cities in the basin of LZB were developed on the base of the total maximum allocated loads (TMALs), which meets the WQ standard of LZB. Four land-sea synchronous investigations were conducted to discern seasonally polluted segments of LZB in 2017. The seriously nitrogen-polluted segments located at southwest and southeast of LZB and the largest area accounted for about 70% of LZB. Due to the heterogeneity of the terrigenous TN load and TMALs of the 13 jurisdictions in the basin, the responsibility apportionment rate for the nitrogen-polluted segments showed a spatial disparity, the city of Weifang with the highest value of 32%, followed by Zibo (28%), Ji’nan (20%), and the other 10 cities (19%). Accordingly, the TN load reduction rate among the 13 jurisdictions varied from 1% to 99%, with an average of 62%. The average values for reduction rate of TN generation, increase rate of TN removal by wastewater treatment, increase rate of TN retention in soil matrix, and TN attenuation in riverway were 44% (21%-69%), 53% (0–88%), 31% (0–61%), and 63% (15–84%), respectively. The three-dimensional seawater quality model simulation results showed that the “precise reduction indicator scheme” was six years earlier than the “equal percent reduction indicator scheme” in each jurisdiction to achieve the WQ standard. Seven cities need to cut emissions more than the current rate. The precise indicators throughout the land-based pollutant entire migration pathway will help implement the TN reduction plan more efficiently.

Fine structure of streamer-to-filament transition in high-pressure nanosecond surface dielectric barrier discharge

Abstract The fine structure of a streamer-to-filament transition in a single-shot high-voltage nanosecond surface dielectric barrier discharge in molecular nitrogen at pressure P = 6 bar was studied with the help of ICCD microimaging. An intermediate discharge structure, existing for only a few nanoseconds, was observed in the time interval between two discharge modes: streamer discharge, with a typical electron density of n e ∼ 1015 cm−3, and filamentary discharge, with n e ∼ 1019 cm−3. The structure was observed for both polarities of the high-voltage electrode. The structure can be briefly described as a stochastic appearance of thin channels propagating a bit faster than the main ionization front of merged surface streamers, transforming in a few nanoseconds in a bi-directional ionization wave. One wave, which we associate with a feather-like structure in optical emission, propagates further away from the high-voltage electrode, and another, a backward wave of emission, propagates back towards the edge of the high-voltage electrode. When the backward wave of emission almost reaches the high-voltage electrode, the filament appears. Plasma properties of the observed structure were studied to better understand the nature of a streamer-to-filament transition. Theoretical analysis suggests that the instability of a flat front of ionization wave (Laplacian instability) triggers the streamer-to-filament transition, and that a surface stem (a tiny region with enhanced electron density) should be in the origin of the bi-directional ionization wave.

Nitrate Regeneration and Loss in the Central Yellow Sea Bottom Water Revealed by Nitrogen Isotopes

The Yellow Sea (YS) is an epicontinental sea framed by the densely populated mainland of China and the Korean peninsula. Human activities over the last decades resulted in heavily increasing discharge of reactive nitrogen into the YS, which created numerous ecological problems. To elucidate the role of central YS in the cycling of reactive nitrogen, specifically the Yellow Sea Cold Water Mass (YSCWM), we determined nutrient concentrations, dual stable isotopes of nitrate (δ15N-NO3- and δ18O-NO3-), and stable isotopes of particulate and sedimentary nitrogen in spring and summer, i.e., in biologically inactive and active periods. The nitrate concentration in spring was higher than that in summer in the northern part of the YSCWM, Nitrate increased in the southern part accompanied by a decrease in δ15N-NO3- and δ18O-NO3-, which are indicative of nitrification that was a significant source of recycled nitrate in the south part of YSCWM. To quantify this regenerated nitrate, we use a mixing model with end members of preformed nitrate in spring and regenerated nitrate in summer, both with their distinct dual isotope values. The results suggest that only 35% nitrate was a residual of nitrate preformed in spring and 65% in summer in the southern branch of YSCWM was regenerated. The northern part of YSCWM has low concentrations of dissolved inorganic nitrogen, mainly because of denitrification in sediments. In contrast, the southern pool of YSCWM is a growing reservoir of regenerated terrestrial reactive nitrogen, the addition of which compensates the removal by co-occurring sediment denitrification. In consequence, the southern branch of YSCWM is facing a higher ecological risk than the northern branch, when excess reactive nitrogen discharge from Changjiang River continues at present levels or even increases.

Exploring Different Pretreatment Methodologies for Allowing Microalgae Growth in Undiluted Piggery Wastewater

The overapplication of manure on agricultural soils leads to nitrogen and phosphorus discharge into the aquatic environment, resulting in serious eutrophication problems and decreased water quality. Piggery wastewater (PWW) can be treated by microalgae to recycle nutrients, but the toxic levels of ammonia and organic matter hinder their growth. Fresh water is usually used to dilute PWW, but it is a scarce resource. The implementation of a pretreatment step before microalgae-based treatment could make PWW suitable for microalgae growth. Electrocoagulation, ammonia stripping, photo-Fenton, and constructed wetlands were evaluated as pretreatment methods to reduce ammonia, chemical oxygen demand (COD), color, and total suspended solids. Moreover, the pretreated PWWs were tested to grow the microalga Tetradesmus obliquus. Photo-Fenton showed the best results among the other pretreatments, achieving removal efficiencies above 90%, except for ammonia. This resulted in T. obliquus being capable of growing on undiluted PWW, even at higher ammonia levels, achieving similar biomass productivity to synthetic medium (66.4 ± 17.8 mg·L−1·day−1 and 60.1 ± 10.4 mg·L−1·day−1, respectively) almost doubling with pH control (116.5 mg·L−1·day−1). Thus, this pretreatment seems to be the most promising one to incorporate into microalgae-based treatment systems and must be further explored.

Nitrate source apportionment and risk assessment: A study in the largest ion-adsorption rare earth mine in China

Nitrate (NO3−) pollution in water bodies has received widespread attention, but studies on nitrogen transformation and pollution risk assessment are still limited, especially in rare earth mining areas. In this study, surface and groundwater samples were collected from the largest rare earth mining site in southern China, and analyzed for the hydrochemical and stable isotopic characteristics. The results showed that the NO3− concentrations ranged from 1.61 to 453.11 mg/L, with 35% of surface water and 53.3% of groundwater samples exceeding the WHO standard (i.e., 50 mg/L). Health risk assessment showed that 31.4% of the water samples had a moderate to high non-carcinogenic risk, and the high-risk areas were concentrated in rare earth mining regions. Additionally, adults were more vulnerable to the non-carcinogenic health risks than children. The high variability of δ15N–NO3- (from −6.43 to 17.09‰) and δ18O–NO3- (from −7.91 to 22.79‰) showed that NO3− was influenced by multiple nitrogen sources and transformation processes. Hydrochemistry and isotopic evidence further indicated that NO3− was primarily influenced by nitrification and hydraulic connection between surface and groundwater. The results of the Bayesian mixing model showed that about 70% of NO3− originated from mine drainage and soil N in the rare earth mining area, while more than 90% of NO3− originated from fertilizer, soil N, and manure and sewage in rural and urban areas in the middle and downstream. This study suggests reducing anthropogenic nitrogen discharge (e.g., leaching agents and fertilizer inputs) as the primary means of NO3− pollution control with biogeochemical processes (e.g., denitrification) to further reduce its pollution.

Microbial Electrochemical Technologies for Sustainable Nitrogen Removal in Marine and Coastal Environments.

For many years, the world’s coastal marine ecosystems have received industrial waste with high nitrogen concentrations, generating the eutrophication of these ecosystems. Different physicochemical-biological technologies have been developed to remove the nitrogen present in wastewater. However, conventional technologies have high operating costs and excessive production of brines or sludge which compromise the sustainability of the treatment. Microbial electrochemical technologies (METs) have begun to gain attention due to their cost-efficiency in removing nitrogen and organic matter using the metabolic capacity of microorganisms. This article combines a critical review of the environmental problems associated with the discharge of the excess nitrogen and the biological processes involved in its biogeochemical cycle; with a comparative analysis of conventional treatment technologies and METs especially designed for nitrogen removal. Finally, current METs limitations and perspectives as a sustainable nitrogen treatment alternative and efficient microbial enrichment techniques are included.

Influence of Nanoparticles and Metal Vapors on the Color of Laboratory and Atmospheric Discharges.

Currently, electrical discharges occurring at altitudes of tens to hundreds of kilometers from the Earth’s surface attract considerable attention from researchers from all over the world. A significant number of (nano)particles coming from outer space burn up at these altitudes. As a result, vapors of various substances, including metals, are formed at different altitudes. This paper deals with the influence of vapors and particles released from metal electrodes on the color and shape of pulse-periodic discharge in air, nitrogen, argon, and hydrogen. It presents the results of experimental studies. The discharge was implemented under an inhomogeneous electric field and was accompanied by the generation of runaway electrons and the formation of mini-jets. It was established that regardless of the voltage pulse polarity, the electrode material significantly affects the color of spherical- and cylindrical-shaped mini jets formed when bright spots appear on electrodes. Similar jets are observed when the discharge is transformed into a spark. It was shown that the color of the plasma of mini-jets is similar to that of atmospheric discharges (red sprites, blue jets, and ghosts) at altitudes of dozens of kilometers and differs from the color of plasma of pulsed diffuse discharges in air and nitrogen at the same pressure. It was revealed that to observe the red, blue and green mini-jets, it is necessary to use aluminum, iron, and copper electrodes, respectively.

Transient behavior of drift and ionization in atmospheric pressure nitrogen discharge

Fluid models are frequently used to describe a non-thermal plasma, such as a streamer discharge. The required electron transport data and rate coefficients for the fluid model are parametrized using local field approximation in first-order models and local-mean-energy approximation in second-order models. We performed Monte Carlo simulations in nitrogen gas with step changes in the E/N (reduced electric field) to study the behavior of the transport properties in the transient phase. During the transient phase of the simulation, we extract the instantaneous electron mean energy, which is different to the steady-state mean electron energy, and the corresponding transport parameters and rate coefficients. Our results indicate that the mean electron energy is not a suitable parameter for mobility/drift of electrons due to the large difference in momentum relaxation and energy relaxation. However, the high-energy threshold rates, such as ionization, show a strong correlation to mean electron energy. In second-order models where the energy-balance equation is solved, we suggest that it would be appropriate to rather use the local electric field to find electron drift velocity in gases such as nitrogen, and the local mean electron energy to determine the ionization and excitation rates.

Dynamics of structure of pulsed discharge in nitrogen and argon at different pressures in a &amp;quot;pin to plane&amp;quot; gap

Using high-speed shooting and shadow photography, the spatial structure of a pulsed discharge in a 1.5 mm long &amp;quot;pin(cathode)-plane&amp;quot; gap in nitrogen and argon in the pressure range from 0.25 to 2 atm was studied. It has been found that a spark discharge is realized in nitrogen and a diffuse form of discharge is realized in argon. For both cases, the presence of a microstructure of discharges in the studied pressure range was found, when the discharge is an aggregation of a large number of micron-diameter channels. It is shown that for each gas the dynamics of the discharge glow structure remains similar at different pressures. It has been established that the glow and microstructure of the discharge in nitrogen are similar to those in air. Keywords: spark discharge, diffuse discharge, microstructure, method of shadow photography, high-speed shooting.