Production Of HNO3 Research Articles

Sustainable nitrogen fixation by novel gliding arc plasma reactor for the production of nitrogen fertilizers

AbstractA novel plasma reactor is being investigated for green NOx production, crucial for nitrate‐based fertilizer manufacturing. Various parameters, including air flow rates, gas ratios, ozone, and catalyst effects are explored for NO → NO2 conversion. NOx concentrations reach ~0.6 vol%, with a total production of ~9.7 gr/h and energy cost of ~3.0 mJ/mol, notably favorable for atmospheric gliding arc plasma. Selectivity (~75%) towards NO2 is achieved with ozone addition or catalytic treatment, pivotal for nitrate fertilizer and HNO3 production.

Modeling the Oxygen Isotope Anomaly (Δ17O) of Reactive Nitrogen in the Community Multiscale Air Quality Model: Insights into Nitrogen Oxide Chemistry in the Northeastern United States.

Atmospheric nitrate, including nitric acid (HNO3), particulate nitrate (pNO3), and organic nitrate (RONO2), is a key atmosphere component with implications for air quality, nutrient deposition, and climate. However, accurately representing atmospheric nitrate concentrations within atmospheric chemistry models is a persistent challenge. A contributing factor to this challenge is the intricate chemical transformations involving HNO3 formation, which can be difficult for models to replicate. Here, we present a novel model framework that utilizes the oxygen stable isotope anomaly (Δ17O) to quantitatively depict ozone (O3) involvement in precursor nitrogen oxides photochemical cycling and HNO3 formation. This framework has been integrated into the US EPA Community Multiscale Air Quality (CMAQ) modeling system to facilitate a comprehensive assessment of NO x oxidation and HNO3 formation. In application across the northeastern US, the model Δ17O compares well with recently conducted diurnal Δ17O(NO2) and spatiotemporal Δ17O(HNO3) observations, with a root mean square error between model and observations of 2.6 ‰ for Δ17O(HNO3). The model indicates the major formation pathways of annual HNO3 production within the northeastern US are NO+OH (46 %), N2O5 hydrolysis (34 %), and organic nitrate hydrolysis (12 %). This model can evaluate NO x chemistry in CMAQ in future air quality and deposition studies involving reactive nitrogen.

Exploring Energy-Efficient Techniques and Chemical Kinetics in Reactive Nitrogen Species Production with Ambient Air Plasma for Plasma-Activated Water

This study investigates the chemical kinetics of reactive nitrogen species (RNS) formation in plasma-activated water (PAW) using ambient air and evaluates its energy efficiency. A singular plasma/liquid reactor was used, with discharge power varying between 16.4 to 27.0 W and agitation speeds set at 0 and 750 rpm. The reactor operated across temperatures from 5.00 to 35.00 °C during a consistent 180 min plasma activation. Analysis encompassed ionic strength effects, hydronium activity, conductivity, and iodide as a redox indicator for PAW. Findings suggest reactive species predominantly originate in the gas phase and move to the liquid through the gas-liquid interface. HNO3 production in PAW demonstrated a zero-order, temperature-dependent reaction. From activation parameters and ionic strength effects, a determinant step for aqueous HNO3 production was proposed. The influence of discharge power and agitation on HNO3 and HNO2 production was associated with heightened rates due to increased mass transfer and electric field strength. The research highlighted a trade-off between energy efficiency and nitrate production rate, emphasizing an efficiency peak of 72.33 nmol J-1 in PAW, pivotal for cost and operational benefits.

Dominant physical and chemical processes impacting nitrate in Shandong of the North China Plain during winter haze events

Nitrate has been a dominant component of PM2.5 since the stringent emission control measures implemented in China in 2013. Clarifying key physical and chemical processes influencing nitrate concentrations is crucial for eradicating heavy air pollution in China. In this study, we explored dominant processes impacting nitrate concentrations in Shandong of the North China Plain during three haze events from 9 to 25 December 2021, named cases P1 (94.46 (30.85) μg m−3 for PM2.5 (nitrate)), P2 (148.95 (50.12) μg m−3) and P3 (88.03 (29.21) μg m−3), by using the Weather Research and Forecasting/Chemistry model with an integrated process rate analysis scheme and updated heterogeneous hydrolysis of dinitrogen pentoxide on the wet aerosol surface (HET−N2O5) and additional nitrous acid (HONO) sources (AS−HONO). The results showed that nitrate increases in the three cases were attributed to aerosol chemistry, whereas nitrate decreases were due mainly to the vertical mixing process in cases P1 and P2 and to the advection process in case P3. HET−N2O5 (the reaction of OH + NO2) contributed 45 % (51 %) of the HNO3 production rate during the study period. AS−HONO produced a nitrate enhancement of 24 % in case P1, 12 % in case P2 and 19 % in case P3, and a HNO3 production rate enhancement of 0.79– 0.97 (0.18– 0.60) μg m−3 h−1 through the reaction of OH + NO2 (HET−N2O5) in the three cases. This study implies that using suitable parameterization schemes for heterogeneous reactions on aerosol and ground surfaces and nitrate photolysis is vital in simulations of HONO and nitrate, and the MOSAIC module for aerosol water simulations needs to be improved.

Heterogeneous catalytic reaction of NO2 to HONO on hematite

The heterogenous catalytic reactions of NO2 on mineral dusts represent one of the important sources of HONO that promote the formation of O3 and other air pollutants, but the mechanism is poorly understood. First principles calculations, including a Hubbard-like +U correction and a dispersion correction, were employed to investigate the heterogeneous interaction of NO2 on the hematite (0001) surface. The competitive adsorption between the most common gas molecules in polluted air (NO2, CO, SO2, O3, H2O, O2, and N2) were also investigated. Under dry conditions, the (NO3δ−)(NOδ+) intermediate species can transform into surface NO3 and gaseous NO. Under wet conditions, the simulations predicted the production of HONO and HNO3 through the hydrolysis of NO2 via (NO3δ−)(NOδ+). Adsorption energies show that the surface Fe site provides strong interactions. Charge transfer occurs from the Fe atom to the adsorbate molecules. This study may facilitate the understanding of the transformations of the atmospheric gas pollutants on naturally occurring mineral dust aerosols. The heterogenous reaction may impact on global atmospheric chemistry.

Interplay between nitrogen oxides and ozone in a filamentary dielectric barrier discharge at various frequencies

AbstractPursuing more efficient nitrogen fixation in the context of the current climate crisis is of prime importance. The Haber‐Bosch process (NH3 production) accounts for at least 2% of the yearly released greenhouse gases. Alternatively, different atmospheric nonthermal discharges have proven their ability to convert nitrogen and oxygen from the air into nitrogen oxides (NO, NO2, and HNO3 hereafter referred as NOx). Among them, dielectric barrier discharges (DBDs) in N2/O2 are very interesting as they are characterized by microdischarges (MDs) developing into filaments under specific conditions (gap length, voltage, frequency, nature of the dielectrics). In this work, we used a sinusoidal voltage at 4, 12, 17.5, and 30 kHz as a key parameter to manipulate the MDs behaviors in an N2/O2 DBD and tailor the chemistry of the discharge. We characterized the MDs distribution by high‐speed camera imaging. Two different nitrogen emission systems, that is, the second positive system (SPS) and the first negative system (FNS), were used to assess the filament temperature and what we define as the delayed‐glow temperature, respectively. The influence of the filament's distribution on the overall discharge temperature has also been evaluated, by using a novel approach allowing the generation of heat distribution maps directly on a thermosensitive paper exposed to the discharge. Finally, the effect of the filaments on ozone (O3) and NOx production has been monitored by in situ Fourier‐transform infrared (FTIR). The DBD can be tuned between homogenously distributed MDs at 4 and 12 kHz to highly localized filaments at 17.5 and 30 kHz. A high filament temperature combined with a cold delayed‐glow is observed at 17.5 kHz while both the filament and the delayed‐glow temperature are high at 30 kHz. Low frequencies lead to heat spreading into the whole discharge volume, while localization of heat along the filament's paths is observed at high frequencies. High‐temperature filaments in the 30 kHz discharge and in the globally heated discharge at low frequencies quickly remove O3 from the discharge and consequently limit the overall NOx production by removing important oxidation pathways. On the contrary, filaments surrounded by cold gas observed at 17.5 kHz allowed to maintain a high concentration of O3 necessary for a faster oxidation of NO and thus increase the HNO3 production, even after 250 s, by avoiding backward reactions.

Catalytic Etching and Oxidation of Platinum Group Metals: Morphology, Chemical Composition and Structure of Pt, Pd and Rh Foils in the O2 Atmosphere and during NH3 Oxidation with Air at 1133 K

Platinum alloy gauzes are employed for the high-temperature oxidation of NH3 to NO used in the industrial production of HNO3 for application in agricultural fertilizers. To enhance the efficiency of NH3 oxidation, various Pt–Pd–Rh alloys are employed for the production of such catalytic gauzes. To understand the role of these metals in NH3 oxidation, scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction were applied to investigate the morphology, composition and structure of Pt, Pd and Rh foils after annealing in O2 and oxidation of NH3 with air at 1133 K. After annealing in O2 and NH3 oxidation, the metallic microgranular structure was detected on Pt(poly), whereas oxide layers of Rh2O3 and PdO were observed on Rh(poly) and Pd(poly). At the onset of NH3 oxidation (t = 1 h), fibrous metal-oxide agglomerates of nanofibers formed on these oxide layers. The long-term (5–10 h) oxidation of NH3 led to the formation of a continuous layer of pyramidal crystals on Rh(poly) and palladium “cauliflowers” on Pd(poly). The highly exothermic reaction of NH3 with oxygen on metals and PdO or Rh2O3 initiates strong catalytic etching forming grains and facets on Pt, fibrous metal-oxide agglomerates, pyramidal crystals and metallic “cauliflowers” on Rh and Pd.

Chemical Composition of the Surface and Subsurface of Pt–Pd–Rh–Ru Catalytic Gauzes Used in the NH3 Oxidation with Air at 1133 K

High-temperature oxidation of NH3 on Pt alloy gauzes to NO is widely employed in industry for the production of HNO3, which is used to obtain agricultural fertilizers. Particular attention is paid now to the investigation of the chemical composition of gauzes used in NH3 oxidation. X-ray photoelectron and energy-dispersive X-ray spectroscopies with the depth of analysis ca. 5 nm and ca. 500 nm were applied to investigate the chemical composition of surface and subsurface layers of the new and used in NH3 oxidation with air at T = 1133 K Pt–Pd–Rh–Ru catalytic gauzes (81, 15, 3.5, 0.5 wt.%, respectively). For all the gauzes, adsorption (OHad, COad), graphitic (Cgr) and oxide (Rh2O3) films were found on the surface of the metallic alloy. Under these films, Cab, Nab and Oab atoms absorbed in the subsurface layers were detected on the gauzes used in NH3 oxidation. The obtained data testify to the penetration of Oab and Nab atoms into deeper layers of the alloy during etching with elevation of the catalyst temperature. Oab atoms were accumulated predominantly on dislocations, etch pits and grain boundaries, whereas Nab atoms intercalated mostly into interstitial sites of the alloy lattice.

An Observational Based Modeling of the Surface Layer Particulate Nitrate in the North China Plain During Summertime

AbstractParticulate nitrate (pNO3−) is an important component in atmospheric fine particulate matter. Here, we present a case study investigating the production and loss processes of pNO3− in surface‐layer based on the observation at a regional site Wangdu in North China Plain (NCP) during summer. The averaged diurnal of nitric acid (HNO3) production reached a maximum of 1.5 μg m−3 h−1 determined from the observed OH and NO2, indicating a fast HNO3 production in the surface layer during the daytime. The chemical processes affecting surface nitrate concentration and daily variation were simulated by a box model based on the Regional Atmospheric Chemical Mechanism version 2 and coupled with the ISORROPIA‐II thermodynamic equilibrium model. The chemical formation of total soluble nitrate (TNO3) at the surface layer cannot explain the fast increase of pNO3− in the morning and overshoot pNO3− in the afternoon, suggesting missing processes in the model. The pNO3− budget analysis suggests the importance of entrainment from residual layer air into the surface layer as an important process for surface pNO3− concentration enhancement in the early morning. In the afternoon, the partition to pNO3− was limited due to the high temperature near the ground. Nevertheless, the observed fast nitrate production still significantly overshot pNO3− in the afternoon. This difference indicates HNO3 production was less efficient throughout the boundary layer than what was observed in the surface layer. Our results highlight the importance of vertical measurements to understand the formation mechanism of nitrate pollution in summer.

Direct Oxidative Nitrogen Fixation from Air and H2 O by a Water Falling Film Dielectric Barrier Discharge Reactor at Ambient Pressure and Temperature.

Current industrial production of HNO3 relies on the Ostwald process via catalytic oxidation of NH3 , which is responsible for the vast bulk of CO2 emission. An attractive alternative route to HNO3 is direct N2 oxidation to aqueous HNO3 , which avoids the NH3 intermediate. Herein, we for the first time report a non-thermal plasma-assisted nitrogen fixation process characteristic of a large gas-liquid contact based on the water falling film dielectric barrier discharge, wherein HNO3 is produced directly from ambient air and H2 O at atmospheric pressure and room temperature without the presence of any catalytic material. By optimizing the plasma reaction conditions, a relatively high synthesis rate and low energy consumption was achieved at the same time with good product selectivity.

Wintertime nitrate formation pathways in the north China plain: Importance of N2O5 heterogeneous hydrolysis

Strict emission control measures have been implemented in the North China Plain (NCP) to improve air quality since 2013. However, heavy particulate matter (PM) pollution still frequently occurs in the region especially during wintertime, and the nitrate contribution to fine PM (PM2.5) has substantially increased in recent several years. Nitrate aerosols, which are formed via nitric acid (HNO3) to balance inorganic cations in the particle phase, have become a major fraction of PM2.5 during wintertime haze events in the NCP. HNO3 is mainly produced through homogeneous (NO2+OH, NO3+VOCs) and heterogeneous pathways (N2O5 heterogeneous hydrolysis) in the atmosphere, but the contribution of the two pathways to the nitrate formation remains elusive. In this study, the Weather Research and Forecasting model with Chemistry (WRF-Chem) was applied to simulate a heavy haze episode from 16 to December 31, 2016 in the North China Plain, and the source-oriented method (SOM) and brute force method (BFM) were both used to evaluate contributions of the heterogeneous pathway to the nitrate formation. The results demonstrated that the near-surface nitrate contributions of the heterogeneous pathway were about 30.8% based on the BFM, and 51.6% based on the SOM, indicating that the BFM might be subject to underestimating importance of the heterogeneous pathway to the nitrate formation. The SOM simulations further showed that the heterogeneous pathway dominated the nighttime HNO3 production in the planetary boundary layer, with an average contribution of 83.0%. Although N2O5 was photolytically liable during daytime, the heterogeneous N2O5 hydrolysis still contributed 10.1% of HNO3, which was caused by substantial attenuation of incident solar radiation by clouds and high PM2.5 mass loading. Our study highlighted the significantly important role of N2O5 heterogeneous hydrolysis in the nitrate formation during wintertime haze days.

High-temperature decomposition of N2O from the HNO3 production: Process feasibility using a structured catalyst

The high-temperature decomposition of N2O in a structured catalyst was studied using a full three-dimensional (3D) model in the temperature range 700–900 °C and high pressure (0.4–0.8 MPa), under realistic gas phase composition, i.e. with 1000 ppm of N2O, high concentrations of NO (9.5–10.5 mol%), O2 (4.5–5.0 mol%), and H2O (15.5–16.8 mol%). The kinetic data gathered from the previous study of the FeOx/Al2O3 catalyst displaying only medium activity were used as the input data. A single-channel 3D model without additional simplifications of fluid flow patterns and mass transfer in fluid and solid catalyst phases was employed to investigate the potential performance of a monolith reactor for N2O decomposition at high temperature regime. The model clearly predicted a relevant performance of the optimized honeycomb system based on such FeOx/Al2O3 catalyst.

Assessment of the seasonal cycle of nitrate in PM2.5 using chemical compositions and stable nitrogen and oxygen isotopes at Nanchang, China

Nitrate (particulate NO3− and gas-phase HNO3) are the primary acidic ions in the atmosphere and play important roles in regional air pollution. However, quantification of the formation pathways of atmospheric nitrate are still poorly understood. Samples of PM2.5 were collected at Nanchang, China, from September 2017 to August 2018. The concentrations of water-soluble ions and the stable isotopic compositions of δ18O-NO3− and δ15N-NO3− were measured. Seasonal values of δ15N-NO3− (autumn:4.4 ± 2.8‰; winter: 6.6 ± 2.4‰; spring: 4.4 ± 2.0‰; summer: 3.1 ± 2.4‰) suggest that seasonal cycles of NO3− in PM2.5 are mainly affected by NOx sources. The highest concentrations of NO3−, aerosol liquid water content (ALWC), Cl−, NH4+, and the lowest concentration of OH were showed during winter. These parameters exhibited opposite trends during summer. δ18O-NO3− values in PM2.5 during autumn (79.2 ± 6.7‰) and spring (73 ± 6.3‰) were between those observed in winter (86.4 ± 5.9‰) and summer (60.7 ± 3.9‰). Values of δ18O-HNO3 endmembers produced via pathway of NO2 + OH (PNO2+OH), pathway of N2O5 + H2O (PN2O5+H2O) and pathways of NO3 + VOCs, N2O5 + Cl−, ClNO3 + H2O and 2NO2 + H2O (Pother) were evaluated during four seasons. The possible fractional contributions of different HNO3 formation pathways to PM2.5NO3− were assessed using the Bayesian isotope mixing model. The results show that the PNO2+OH contributes to 59 ± 5% and 12 ± 6% of HNO3 production during summer and winter, respectively. The possible fractional contributions of PN2O5+H2O in all seasons are comparable, but the contributions of Pother in winter are higher than those during summer. This study suggested that Pother may be important for wintertime NO3− formation and provides potential information for using chemical models to simulate atmospheric NO3− formation.

Sensitivity of Ozone Production to NOx and VOC Along the Lake Michigan Coastline

AbstractWe report on the sensitivity of enhanced ozone (O3) production, observed during lake breeze circulation along the coastline of Lake Michigan, to the concentrations of nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs). We assess the sensitivity of O3 production to NOx and VOC on a high O3 day during the Lake Michigan Ozone Study 2017 using an observationally constrained chemical box model that implements the Master Chemical Mechanism (MCM v3.3.1) and recent emission inventories for NOx and VOCs. The Master Chemical Mechanism model is coupled to a backward air mass trajectory analysis from a ground supersite in Zion, IL, where an extensive series of measurements of O3 precursors and their oxidation products, including hydrogen peroxide (H2O2), nitric acid (HNO3), and particulate nitrates (NO3−) serve as model constraints. We evaluate the chemical evolution of the Chicago‐Gary urban plume as it advects over Lake Michigan and demonstrate how modeled indicators of VOC‐ versus NOx‐sensitive regimes can be constrained by measurements at the trajectory endpoint. Using the modeled ratio of the instantaneous H2O2 and HNO3 production rates (PH2O2/PHNO3), we suggest that O3 production over the urban source region is strongly VOC sensitive and progresses towards a more NOx‐sensitive regime as the plume advects north along the Lake Michigan coastline on this day. We also demonstrate that ground‐based measurements of the mean concentration ratio of H2O2 to HNO3 describe the sensitivity of O3 production to VOC and NOx as the integral of chemical production along the plume path.

On the contribution of nocturnal heterogeneous reactive nitrogen chemistry to particulate matter formation during wintertime pollution events in Northern Utah

Abstract. Mountain basins in Northern Utah, including the Salt Lake Valley (SLV), suffer from wintertime air pollution events associated with stagnant atmospheric conditions. During these events, fine particulate matter concentrations (PM2.5) can exceed national ambient air quality standards. Previous studies in the SLV have found that PM2.5 is primarily composed of ammonium nitrate (NH4NO3), formed from the condensation of gas-phase ammonia (NH3) and nitric acid (HNO3). Additional studies in several western basins, including the SLV, have suggested that production of HNO3 from nocturnal heterogeneous N2O5 uptake is the dominant source of NH4NO3 during winter. The rate of this process, however, remains poorly quantified, in part due to limited vertical measurements above the surface, where this chemistry is most active. The 2017 Utah Winter Fine Particulate Study (UWFPS) provided the first aircraft measurements of detailed chemical composition during wintertime pollution events in the SLV. Coupled with ground-based observations, analyses of day- and nighttime research flights confirm that PM2.5 during wintertime pollution events is principally composed of NH4NO3, limited by HNO3. Here, observations and box model analyses assess the contribution of N2O5 uptake to nitrate aerosol during pollution events using the NO3- production rate, N2O5 heterogeneous uptake coefficient (γ(N2O5)), and production yield of ClNO2 (φ(ClNO2)), which had medians of 1.6 µg m−3 h−1, 0.076, and 0.220, respectively. While fit values of γ(N2O5) may be biased high by a potential under-measurement in aerosol surface area, other fit quantities are unaffected. Lastly, additional model simulations suggest nocturnal N2O5 uptake produces between 2.4 and 3.9 µg m−3 of nitrate per day when considering the possible effects of dilution. This nocturnal production is sufficient to account for 52 %–85 % of the daily observed surface-level buildup of aerosol nitrate, though accurate quantification is dependent on modeled dilution, mixing processes, and photochemistry.

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.

Femtosecond filamentation induced particles and their cloud condensation nuclei activity

Laboratory experiments were conducted to investigate femtosecond filamentation induced particle formation and growth in particle-free air as well as in the presence of pre-existing ammonium sulfate aerosols. The ability of laser induced particles to act as cloud condensation nuclei (CCN) was explored. The influence of water vapor and the pulse energy on the production efficiency and activation properties of particles were also examined. In particle-free air, laser filaments could lead to a significant production of new particles, the number concentration of which was comparable to or larger than that in polluted ambient air, depending upon the pulse energy and humidity. Total particle number and mass concentrations within 20–708 nm were predominantly contributed by particles with a diameter smaller than 100 nm. Remarkably high NOx up to an order of ∼101 ppm was generated in the chamber, allowing sufficient production of HNO3 and probably subsequent HNO3-H2O binary nucleation. In the presence of pre-existing particles, the yield of particle number was largely enhanced in laser filaments, especially in humid air. Particle number size distribution shifted towards smaller particle size, leading to a slight increase in particle mass. It was found that a considerable portion of laser induced particles, no matter generated with or without pre-existing particles, could act as CCN. The amount of CCN at 0.80% supersaturation was in the magnitude of 104∼105 cm−3 in all experiments, nearly one order larger than the average ambient level even in severely polluted regions. Overall, increasing the pulse energy and water vapor would favor particle formation and growth as well as the production of CCN. Raising the pulse energy also resulted in a decline of the hygroscopic parameter κ, implying the modification of aerosol chemical composition. Though more investigative studies are still needed to explore mechanisms underlying some of these experimental results, laser filaments are undoubtedly capable of inducing substantial particle formation and modifying microphysical/chemical properties of pre-existing particles. By influencing these crucial properties and thereby aerosol direct/indirect climatic and environmental effects, laser filamentation would provide a promising potential for related atmospheric applications.

Electrochemical synthesis of nitric acid from air and ammonia through waste utilization.

ABSTRACTCommercial nitric acid (HNO3) and ammonia (NH3) are mostly produced through the Ostwald process and the Haber-Bosch process, respectively. However, high energy demand and enormous greenhouse gas accompy these processes. The development of economical and green ways to synthesize HNO3 and NH3 is highly desirable for solving the global energy and environmental crisis. Here, we present two energy-efficient and environmentally friendly strategies to synthesize HNO3 and NH3 at distributed sources, including the electrocatalytic oxidation of N2 in air to HNO3 and the electrocatalytic reduction of residual n}{}{rm NO_{3}^{-}} contamination in water to NH3. The isotope-labeling studies combined with theoretical calculation reveal the reaction path of the two proposed strategies, confirming the origin of the electrochemical products. Importantly, the electrooxidation-generated n}{}{rm NO_{3}^{-}} ions may also serve as reactants for the electroreduction synthesis of NH3 in the future. Our work may open avenues for energy-efficient and green production of HNO3 and NH3 at distributed sources.

Femtosecond laser filament-assisted AgI-type pyrotechnic nucleant-induced water condensation in cloud chamber.

AgI-type pyrotechnics are widely used in the field of weather modification, as a kind of artificial ice nuclei. However, their precipitation yield remains an intensively studied area. In this paper, we present a study of AgI-type pyrotechnic nucleant-induced water condensation promoted by femtosecond laser filaments in a cloud chamber. It is found that when 50-ml sample was irradiated by the laser filaments, the particles condensed on the glass slide are more soluble and slightly larger (5-15 μm). The irradiation of the laser filament on the nucleant rarely induces the generation of particles of sizes larger than 1 μm; however, it increases the decay time of particles from 13 to 18 min by the creation of numerous small particles. The amount of snow on the cold bottom plate increases by 4.2-13.1% in 2 h, compared to that without the irradiation of the laser filament. These results are associated with the production of high-concentration HNO3 by the laser filament. The concentration of HNO3 in the melt water increases by more than ten times when the sample was irradiated by the laser filaments.

Modeling NH4NO3 Over the San Joaquin Valley During the 2013 DISCOVER-AQ Campaign.

The San Joaquin Valley (SJV) of California experiences high concentrations of particulate matter NH4NO3 during episodes of meteorological stagnation in winter. A rich data set of observations related to NH4NO3 formation was acquired during multiple periods of elevated NH4NO3 during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field campaign in SJV in January and February 2013. Here NH4NO3 is simulated during the SJV DISCOVER-AQ study period with the Community Multiscale Air Quality (CMAQ) model, diagnostic model evaluation is performed using the DISCOVER-AQ data set, and integrated reaction rate analysis is used to quantify HNO3 production rates. Simulated NO3- generally agrees well with routine monitoring of 24-hr average NO3-, but comparisons with hourly average NO3- measurements in Fresno revealed differences at higher time resolution. Predictions of gas-particle partitioning of total nitrate (HNO3 + NO3-) and NHx (NH3 + NH4+) generally agree well with measurements in Fresno, although partitioning of total nitrate to HNO3 is sometimes overestimated at low relative humidity in afternoon. Gas-particle partitioning results indicate that NH4NO3 formation is limited by HNO3 availability in both the model and ambient. NH3 mixing ratios are underestimated, particularly in areas with large agricultural activity, and additional work on the spatial allocation of NH3 emissions is warranted. During a period of elevated NH4NO3, the model predicted that the OH + NO2 pathway contributed 46% to total HNO3production in SJV and the N2O5 heterogeneous hydrolysis pathway contributed 54%. The relative importance of the OH + NO2 pathway for HNO3 production is predicted to increase as NOx emissions decrease.