Gas-phase NO Research Articles

Catalytic Ozonation of Low Concentration Toluene over MnFeOx-USY Catalyst: Effects of Interactions between Catalytic Components and Introduction of Gas Phase NOx.

A series of Mn and Fe metal oxide catalysts loaded onto USY, as well as single metal oxides, were prepared and characterized. The effects of interactions between the catalytic components and the introduction of gas phase NO on the catalytic ozonation of toluene were investigated. Characterization showed that there existed strong interactions between MnOx, FeOx, and USY, which enhanced the content of oxygen vacancies and acid sites of the catalysts and thus boosted the generation of reactive oxygen species and the adsorption of toluene. The MnFeOx-USY catalyst with MnOx and FeOx dimetallic oxides exhibited the most excellent performance of catalytic ozonation of toluene. On the other hand, the presence of NOx in reaction gas mixtures significantly promoted both toluene conversion and mineralization, which was attributed to the formation of nitrate species on the catalysts surface and thus the increase of both acid sites and toluene oxidation sites. Meanwhile, the reaction mechanism between O3 and C7H8 was modified in which the strong interactions between MnOx, FeOx, and USY accelerated the reaction progress based on the L-H route. In addition, the formation of the surface nitrate species not only promoted reaction progress following the L-H route but also resulted in the occurrence of the reaction via the E-R route.

Surface fluorinated anatase TiO2 nanosheets for NO deep oxidation in O3/H2O2 system: Enhanced mechanism and oxidation characteristics

O3 technology has exhibited promise in removing NO at low-temperature. However, challenges of high NO2 concentration that are difficult to absorb due to insufficient O3 oxidizing capacity remains. Herein, we reported an efficient strategy to generate oxygen-containing radicals for NO deep oxidation via fluorine and {001} facets modulated anatase TiO2 triggering highly activity sites that catalyzed O3/H2O2 to address the above issue. The strong electron withdrawing effect of F sites enhanced the deprotonation of H2O2, while Ti5c on {001} surface exhibited strong Lewis acid to activate O3, thermal stabilization treatment of the catalyst strengthened the synergistic effect of F and Ti5c, resulting in a 97 % NO deep oxidation efficiency at 100 °C with 3 % water vapor content. Additionally, the oxidation characteristics of the radicals was carefully discussed by occupying NO adsorption sites on TiO2 surface, the result revealed that radicals could remarkably react with gas-phase NO. Finally, the synergistic effect and oxidation properties would possess guiding significance for improving NO oxidation and applications.

Antigen stasis and airway nitrosative stress in human primary ciliary dyskinesia.

Nasal nitric oxide (nNO) is low in most patients with primary ciliary dyskinesia (PCD). Decreased ciliary motion could lead to antigen stasis, increasing oxidant production and NO oxidation in the airways. This could both decrease gas phase NO and increase nitrosative stress. We studied primary airway epithelial cells from healthy controls (HCs) and patients with PCD with several different genotypes. We measured antigen clearance in fenestrated membranes exposed apically to the fluorescently labeled antigen Dermatophagoides pteronyssinus (Derp1-f). We immunoblotted for 3-nitrotyrosine (3-NT) and for oxidative response enzymes. We measured headspace NO above primary airway cells without and with a PCD-causing genotype. We measured nNO and exhaled breath condensate (EBC) H2O2 in vivo. Apical Derp1-f was cleared from HC better than from PCD cells. DUOX1 expression was lower in HC than in PCD cells at baseline and after 24-h Derp1-f exposure. HC cells had less 3-NT and NO3- than PCD cells. However, NO consumption by HC cells was less than that by PCD cells; NO loss was prevented by superoxide dismutase (SOD) and by apocynin. nNO was higher in HCs than in patients with PCD. EBC H2O2 was lower in HC than in patients with PCD. The PCD airway epithelium does not optimally clear antigens and is subject to oxidative and nitrosative stress. Oxidation associated with antigen stasis could represent a therapeutic target in PCD, one with convenient monitoring biomarkers.NEW & NOTEWORTHY The PCD airway epithelium does not optimally clear antigens, and antigen exposure can lead to NO oxidation and nitrosative stress. Oxidation caused by antigen stasis could represent a therapeutic target in PCD, and there are convenient monitoring biomarkers.

NO formation by N2/O2 plasma catalysis: The impact of surface reactions, gas-phase reactions, and mass transport

Pathways and timescales relevant to facilitate plasma-assisted N2-O2 reactions are assessed by measuring the consumption of plasma-derived N and the formation of NO in the gas phase and over Ag catalytic surfaces. These measurements are enabled by a setup that enables N2 activation in an atmospheric pressure RF plasma jet, enables O2 addition in the plasma afterglow, facilitates reactions over an Ag wire catalyst, and allows species density quantification by molecular beam mass spectrometry. Gas-phase reactions consume N but do not form NO with high selectivity. The presence of the non-porous Ag wire catalyst increases the rate of N conversion to NO, though mass transfer processes, not surface reactions, dictate the rate of N consumption. When O2 concentrations and the ratio of the surface area of the catalyst to the void volume of the reactor are high (3–5 mol% O2, 10900 m−1), N conversion to NO reaches 100 % selectivity. When both N2 and O2 are fed through the plasma jet, gas-phase NO production increases 10×, although plasma and gas-phase processes do not exclusively produce NO. Above a threshold NO density, N cannot diffuse to the catalyst surface faster than it is consumed in the gas phase by reactions with NO. Thus, the use of heterogeneous catalysts to enhance plasma-driven NxOy formation and control NxOy product selectivity is limited to cases where diffusive transport of N from the gas phase to the catalyst surface is faster than consumption of N from gas-phase reactions with NO.

Technical note: Gas-phase nitrate radical generation via irradiation of aerated ceric ammonium nitrate mixtures

Abstract. We present a novel photolytic source of gas-phase NO3 suitable for use in atmospheric chemistry studies that has several advantages over traditional sources that utilize NO2 + O3 reactions and/or thermal dissociation of dinitrogen pentoxide (N2O5). The method generates NO3 via irradiation of aerated aqueous solutions of ceric ammonium nitrate (CAN, (NH4)2Ce(NO3)6) and nitric acid (HNO3) or sodium nitrate (NaNO3). We present experimental and model characterization of the NO3 formation potential of irradiated CAN / HNO3 and CAN / NaNO3 mixtures containing [CAN] = 10−3 to 1.0 M, [HNO3] = 1.0 to 6.0 M, [NaNO3] = 1.0 to 4.8 M, photon fluxes (I) ranging from 6.9 × 1014 to 1.0 × 1016 photons cm−2 s−1, and irradiation wavelengths ranging from 254 to 421 nm. NO3 mixing ratios ranging from parts per billion to parts per million by volume were achieved using this method. At the CAN solubility limit, maximum [NO3] was achieved using [HNO3] ≈ 3.0 to 6.0 M and UVA radiation (λmax⁡ = 369 nm) in CAN / HNO3 mixtures or [NaNO3] ≥ 1.0 M and UVC radiation (λmax⁡ = 254 nm) in CAN / NaNO3 mixtures. Other reactive nitrogen (NO2, N2O4, N2O5, N2O6, HNO2, HNO3, HNO4) and reactive oxygen (HO2, H2O2) species obtained from the irradiation of ceric nitrate mixtures were measured using a NOx analyzer and an iodide-adduct high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). To assess the applicability of the method for studies of NO3-initiated oxidative aging processes, we generated and measured the chemical composition of oxygenated volatile organic compounds (OVOCs) and secondary organic aerosol (SOA) from the β-pinene + NO3 reaction using a Filter Inlet for Gases and AEROsols (FIGAERO) coupled to the HR-ToF-CIMS.

Formation of nitrogen-containing gas phase products from the heterogeneous (photo)reaction of NO2 with gallic acid

Heterogeneous reaction of gas phase NO2 with atmospheric humic-like substances (HULIS) is potentially an important source of volatile organic compounds (VOCs) including nitrogen (N)-containing compounds, a class of brown carbon of emerging importance. However, the role of ubiquitous water-soluble aerosol components in this multiphase chemistry, namely nitrate and iron ions, remains largely unexplored. Here, we used secondary electrospray ionization ultrahigh-resolution mass spectrometry for real-time measurements of VOCs formed during the heterogeneous reaction of gas phase NO2 with a solution containing gallic acid (GA) as a proxy of HULIS at pH 5 relevant for moderately acidic aerosol particles. Results showed that the number of detected N-containing organic compounds largely increased from 4 during the NO2 reaction with GA in the absence of nitrate and iron ions to 55 in the presence of nitrate and iron ions. The N-containing compounds have reduced nitrogen functional groups, namely amines, imines and imides. These results suggest that the number of N-containing compounds is significantly higher in deliquescent aerosol particles due to the influence of relatively higher ionic strength from nitrate ions and complexation/redox reactivity of iron cations compared to that in the dilute aqueous phase representative of cloud, fog, and rain water.

Pyrolysis behavior, properties and mechanism of high-energy oxidizer 2,3-bis(hydroxymethyl)-2,3-dinitro-1,4-butanediol tetranitrate

To evaluate the thermal properties and promote the application of 2,3-bis(hydroxymethyl)-2,3-dinitro-1,4-butanediol tetranitrate (BHDBT), thermal behavior of BHDBT was studied systematically using differential scanning calorimetry (DSC), thermogravimetric analysis (TG/DTG) and thermogravimetric-infrared-mass spectrometry (TG-IR-MS) techniques. The results show that the thermal behavior of BHDBT presents two stages, one is an obvious endothermic melting process, the other is a big exothermic decomposition process with mass loss of about 81 %, and the peak temperatures (Tp) of two processes are 86.5 °C and 186.9 °C at the heating rate of 10 °C min−1, respectively. In high-pressure sealed crucible, BHDBT presents similar thermal behavior to that in common open crucible. Non-isothermal decomposition kinetics equation of BHDBT was obtained, and the possible thermal decomposition mechanism for BHDBT was proposed based on the main gas-phase products, including H2O, HCN, CO, CO2, NO, N2O and NO2, which are proved by TG-IR-MS testing results. Finally, the combustion heat and standard molar enthalpy of formation of BHDBT were measured and calculated. All results will provide a theoretical support for the application of BHDBT.

Electrochemically-mediated reactive separation of nitric oxide into nitrate using iron chelate

Valorization of nitric oxide is a promising solution for addressing the environmental and resource issues related to the nitrogen cycle. However, low concentrations of nitric oxide combined with impurities in exhaust streams limit its potential, and it requires extensive energy to produce high-purity nitric oxide. Here, we propose a synergistic reactive separation system that combines iron-chelate selective absorption with an electrochemical reaction to convert nitric oxide to nitrate. Among the iron-based chelates tested, EDTA was found to be the most effective in capturing gas-phase nitric oxide. Direct electrochemical oxidation of Fe-EDTA-NO solution exhibited Faradaic efficiency and a partial current density toward nitrate of 70% and 30.1 mA cm−2 at 2.2 V vs RHE and pH 7, resulting in a 43-fold enhancement of nitrate partial current density and a 2-fold improvement in Faradaic efficiency compared to simple purging without selective absorbent. Nitrate was then selectively recovered from the Fe-EDTA system using simple polarity reversal following electrooxidation with a separation factor of 13 over background sulfate. This study offers a new approach to gas-phase NO remediation and valorization using an electrified means.

Effect of migration of ZCu(OH) to Z2Cu upon hydrothermal aging on the NH3-SCR reaction mechanism over a Cu-CHA catalyst

In this study, the experiments combined with activity tests and characterizations were conducted to investigate the influence of hydrothermal aging (HTA) on the reactivity of NH3-SCR over a Cu-CHA catalyst. The results showed that the NOx conversion efficiency can reach more than 80% below 225 ℃ in the reaction between NH3 and NO+O2 after hydrothermal aging, but it increases the N2O production. The wave spectrum of in-situ DRIFTs confirmed the notable differences in the NH3-SCR mechanism between Cu species of ZCu(OH) and Z2Cu at the same reaction conditions. The NH3-SCR reaction occurring on ZCu(OH) followed the ‘Langmuir-Hinshelwood’ (L-H) mechanism, where NH3 combined with products that oxidize NO to NO2 via dimerization and disproportionation reactions to produce the key intermediates as NH4NO2 and HONO. However, the entire NH3-SCR on Z2Cu followed the ‘Eley-Rideal’ (E-R) mechanism, in which adsorbed NH3 effectively reacted with gas-phase NO to form H2NNO and then produced N2.

Observations of microphysical properties and radiative effects of a contrail cirrus outbreak over the North Atlantic

Abstract. Contrail cirrus constitute the largest radiative forcing (RF) component to the total aviation effect on climate. However, the microphysical properties and radiative effects of contrail cirrus and natural cirrus clouds in the same meteorological conditions are still not completely resolved. Motivated by these uncertainties, we investigate an extended cirrus region perturbed by aviation in the North Atlantic region (NAR) on 26 March 2014 during the Midlatitude Cirrus (ML-CIRRUS) experiment. On that day, high air traffic density in the NAR combined with large scale cold and humid ambient conditions favored the formation of a contrail cirrus outbreak situation. In addition, low coverage by low-level water clouds and the homogeneous oceanic albedo increased the sensitivity for retrieving cirrus properties and their radiative effect from satellite remote sensing. This allowed us to extend the current knowledge on contrail cirrus by combining airborne in situ, lidar and satellite observations. In the synoptic context of a ridge cirrus, an extended thin ice cloud with many persistent contrails and contrail cirrus has been observed for many hours with the geostationary Meteosat Second Generation (MSG)/Spinning Enhanced Visible and InfraRed Imager (SEVIRI) from the early morning hours until dissipation after noon. Airborne lidar observations aboard the German High Altitude and LOng Range Research Aircraft (HALO) suggest that this cirrus has a significant anthropogenic contribution from aviation. A new method based on in situ measurements was used to distinguish between contrails, contrail cirrus and natural cirrus based on ice number and gas phase NO concentrations. Results show that contrail effective radii (Reff) reach at most 11 µm, while contrail cirrus Reff can be as large as 51 µm. Contrail and contrail cirrus mean Reff is 18 % smaller than that of natural cirrus. We find that a difference in Reff between contrail cirrus and natural cirrus survives in this contrail cirrus outbreak event. As for radiative effects, a new method to estimate top-of-atmosphere instantaneous RF in the solar and thermal range is developed based on radiative transfer model simulations exploiting in situ and lidar measurements, satellite observations and ERA5 reanalysis data for both cirrus and cirrus-free regions. Broadband irradiances estimated from our simulations compare well with satellite observations from MSG, indicating that our method provides a good representation of the real atmosphere and can thus be used to determine the RF of ice clouds. For a larger spatial area around the flight path, we find that the contrail cirrus outbreak is warming in the early morning and cooling during the day. The methods presented here and the results will be valuable for future research to constrain uncertainties in the assessment of radiative impacts of contrail cirrus and natural cirrus and for the formulation and evaluation of contrail mitigation options.

Reactive Uptake of Gas-Phase NO2 by Urban Road Dust in the Dark.

Road dust constitutes a prominent source of anthropogenic particulate matter, making its heterogeneous interactions with common atmospheric gas-phase compounds important. Here, we show that three distinct samples of urban road dust-including dust samples collected from city streets in summer and winter, and an urban park in summer-react with NO2 in the dark, forming NO and surface nitrite. The loss of NO2 ranged from ∼2 to 13% of its gas-phase concentration and scaled with its concentration as well as with the mass of the road dust sample. The uptake of NO2 by the winter dust was ∼4 times greater than that seen from summer street dust, which was in turn greater than that by the park dust. The conversion ratio of NO2 → NO ranged from 0.06 to 0.8 NO produced per NO2 lost and was greatest for the summer park dust. Exposure of the summer road dust to NO2 roughly doubles the concentration of inorganic nitrite anion in the dust but does not produce nitrate. The formation of NO and photolabile nitrite products means that heterogeneous NO x reactions occurring on the surface of road dust in the dark could have wide implications for the oxidative potential of urban areas.

Composite TiO2-based photocatalyst with enhanced performance.

TiO2 is the most studied photocatalyst because of its non-toxicity, chemical stability, and low cost. However, the problem of TiO2 is its low activity in the visible region of the spectrum. In this study, we focused on the preparation of composite photocatalytic materials with altered light absorption properties. TiO2 P25 and various metal oxides were mechanically joined by ball-milling and immobilized on glass plates. The prepared samples were evaluated based on their ability to degrade NO in gas phase. The formation of undesirable byproducts was also investigated. Four best performing composites were later chosen, characterized, and further evaluated under various conditions. According to their performance, the metal oxide additives can be divided into three groups. P25/Fe2O3 showed the most promising results-an increase in overall deNOx activity under modified ISO conditions and altered selectivity (less NO2 is formed) under both simulated outdoor and simulated indoor conditions. On the other hand, P25/V2O5 composite showed negligible photocatalytic activity. The intermediate group includes P25/WO3 and P25/ZnO photocatalysts, whose performances are similar to those of pristine P25.

Gas-Particle Uptake and Hygroscopic Growth by Organosulfate Particles

Organosulfate compounds make up a substantial fraction of the particle mass concentration in some regions of the Earth’s atmosphere, and organosulfate particles can have sufficiently high viscosity to limit rates of gas-particle interactions. Viscosity varies with relative humidity (RH). Herein, organosulfate particles were exposed to the gas-phase products of α-pinene photooxidation. The gas-particle partitioning of these species was studied from 15 to 70% RH and <1 to 16 ppb NO at 299 K. The uptake of the α-pinene oxidation products increased with the increase in RH, and higher gas-phase NO concentrations resulted in increased particle-phase concentrations of nitrogen compounds. Particle hygroscopicity was examined by optical microscopy. Hygroscopic growth at elevated RH was sufficient to explain the RH-dependent uptake measurements, and kinetic limitations tied to particle viscosity were not observed. The lack of kinetic limitations combined with the Stokes–Einstein equation implied a viscosity much less than 1 × 106 Pa s. This value is consistent with estimated viscosities based on literature parameterizations for water mass fractions in the particles of at least 0.05 at 15% RH. Overall, these results suggest that organosulfate hygroscopicity plays a key role in their viscosity and hence in regulating gas-particle partitioning, thereby simplifying the treatment of atmospheric chemistry and transport of pollutants in models of the Earth’s atmosphere. The role of organosulfates is expected to take on increasing importance for projected future emission trends.

Synergistic catalytic elimination of NO, mercury and chlorobenzene over WCeMnOx/TiO2-ZrO2: Performance study of pore structure

The catalytic performance of synergistic catalytic elimination of NO, mercury and chlorobenzene for WCeMnOx/TiO2-ZrO2 was improved by controlling the pore structure. The formation of micron-sized macropores made the catalyst structure looser, and the transparent macropores helped the catalyst expose more active sites. At low temperature, -NH2* reacted with monodentate nitrite and bidentate nitrate, and NH4+ reacted with gas phase NO to generate N2 and H2O. At high temperature, NH4+ reacted rapidly with gas phase NO. The reaction process of catalytic oxidation of Hg0 was that gaseous Hg0 was adsorbed on the catalyst surface and then oxidized to Hg2+. For the catalytic degradation of chlorobenzene, phenols and HCl were generated firstly, and then phenols and hydroxyl groups reacted to form maleate, bidentate carbonate and carbonate species. The maleate and bidentate carbonate degraded to form carbonate, and the carbonate degraded to produce CO2 and H2O.

Nitro-oxidation process for fabrication of efficient bioadsorbent from lignocellulosic biomass by combined liquid-gas phase treatment

A sequential treatment involving HNO3 delignification in liquid phase and NO2-induced cellulose oxidation in gas phase was applied to raw jute fibers. The structure, chemical compositions, morphology and surface properties of the treated materials in each step were systematically characterized. First, delignification of jute fibers could occur at a mild HNO3 condition (30%, 25 °C, 6 h), capable of removing a significant portion of lignin without changing the native cellulose I structure. Subsequently, gas-phase NO2 treatment can oxidize partially delignified jute fibers and produce high concentrations of carboxyl groups (1.31–1.45 mmol/g) on the material surface, comparable to TEMPO-mediated oxidation. The resultant material is effective in removing positively charged contaminants, such as Thallium(I) ions from water (the removal efficiency >80%). The mixed liquid-gas phase nitro-oxidation process (NOP) provides better control of cellulose oxidation for fabrication of water remediation adsorbents from lignocellulose biomass and further reduces the energy and water consumption since there is no requirement for washing the oxidized cellulose after gas-phase NO2 treatment.

Surface Structures of Fe-TiO2 Photocatalysts for NO Oxidation.

Commercial rutile TiO2 particles capped with Al2O3 and ZrO2 layers, which are widely used in white pigments, can serve as a starting material for the fabrication of visible light-responsive photocatalysts toward gas-phase NO oxidation. The as-received TiO2 with iron impurities exhibited reduced photocatalytic activity, and the activity was boosted by the deposition of additional iron comparable in quantity to the intrinsic iron impurity level. Analyses using X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectroscopy, and low-energy ion scattering spectroscopy revealed that the deposited iron and intrinsic impurity iron are dissimilar in terms of location, oxidation states, and interaction with TiO2. This suggests that tracking the structure and impurity levels of photocatalyst elements can be crucial for understanding structure-activity relationships of real catalysts.

Theoretical investigations of the interaction between diatomic molecules and coinage metal atoms

In this contribution, we investigate the nature of the electronic interaction between gas phase CO and NO with coinage metal atoms {Cu, Ag, Au} in different charge states. The electronic structure is first characterised by means of state-of-the-art coupled-cluster calculations for a wide range of configurations. An analytical Reactive Bond Order (REBO) force field is used to fit the data, revealing a strong corrugation of the potential energy landscape in some cases. The fundamental vibrational bands are variationally computed for the different system. It is found that the metal determines the binding interaction and the spectroscopic signature of the complexes, as well as their structure and geometry.

Atmospheric Occurrence of Particle-associated Nitrotriphenylenes via Gas-phase Radical-initiated Reactions Observed in South Osaka, Japan

Nitrotriphenylenes (NTPs), which include the highly mutagenic isomer 2-nitrotriphenylene (2-NTP), have been detected in airborne particles. From a public hygienic point of view, it is necessary to study the environmental occurrence of NTPs in detail. In this study, concentrations of five nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) including NTPs in airborne particles and of nitrogen oxides (NOx; NO+NO2) and carbon monoxide (CO), at a location in South Osaka, Japan, were measured at 3 h intervals. It was found that the diurnal variations in the concentrations of 1-nitropyrene (1-NP), NOx, and CO were similar, being high early in the morning and late in the evening. This finding indicates that the occurrence of 1-NP is affected significantly by primary emissions, particularly by automotive emissions. The concentration change in 1-nitrotriphenylene was similar to that of 2-nitropyrene produced by an atmospheric OH radicalinitiated reaction. On the contrary, the variations in the concentrations of 2-nitrofluoranthene (2-NF) and 2-NTP were significantly different from those of the other nitro-PAHs, i.e., their concentrations increased during the nighttime, suggesting that neither 2-NF nor 2-NTP was emitted from the primary sources, but were formed via the NO3 radicalinitiated nitration of the parent fluoranthene and triphenylene (TP) in the atmosphere. Based on the ambient concentration of 2-NTP and the reported rate constant for the reaction of TP with NO3 radicals, the yield of 2-NTP from the gas-phase NO3 radical-initiated reaction of TP was estimated to be 23%.

Influence of vegetation on occurrence and time distributions of regional new aerosol particle formation and growth

Abstract. The occurrence frequency of regional atmospheric new aerosol particle formation and consecutive growth events (fNPF) were studied with respect to vegetation activity, aerosol properties, air pollutants and meteorological data in Budapest over the time interval from 2008 to 2018. The data set evaluated contained results of in situ measurements on the land surface that were mostly performed at the Budapest platform for Aerosol Research and Training Laboratory, of satellite-based products recorded by MODIS on Terra and of modelled vegetation emission-related properties from an advanced regional biogeochemical model. The annual mean relative occurrence frequencies were considerable (with an overall mean of 21 %), remained at a constant level (with an overall SD of 5 %) and did not exhibit tendentious change over the years. The shape of the distributions of monthly mean fNPF exhibited large variability from year to year, while the overall average distribution already possessed a characteristic pattern. The structure of the new particle formation (NPF) occurrence distributions was compared to those of environmental variables including concentrations of gas-phase H2SO4, SO2, O3, NO, NO2, CO, PM10 mass and NH3; particle numbers in the size fractions of 6–1000, 6–100 and 100–1000 nm; condensation sink; air temperature (T); relative humidity (RH); wind speed (WS); atmospheric pressure (P); global solar radiation (GRad); gross primary production (GPP) of vegetation; leaf area index (LAI); and stomatal conductance (SCT). There were no evident systematic similarities between fNPF on the one hand and all of the variables studied on the other hand, except for H2SO4 and perhaps NH3. The spring maximum in the NPF occurrence frequency distribution often overlapped with the time intervals of positive T anomaly in vegetated territories. The link between the potential heat stress exerted on plants in sultry summer intervals and the summer fNPF minimum could not be proven. The relevance of environmental variables was assessed by their ratios on NPF event days and on non-event days. The gas-phase H2SO4 concentration showed the largest monthly ratios, followed by O3. The WS, biogenic precursor gases and SO2 can generally favour NPF events, although their influence seemed to be constrained. An association between the fNPF and vegetation growth dynamics was clearly identified.

Nitromethane Decomposition via Automated Reaction Discovery and an Ab Initio Corrected Kinetic Model.

We explore the systematic construction of kinetic models from in silico reaction data for the decomposition of nitromethane. Our models are constructed in a computationally affordable manner by using reactions discovered through accelerated molecular dynamics simulations using the ReaxFF reactive force field. The reaction paths are then optimized to determine reaction rate parameters. We introduce a reaction barrier correction scheme that combines accurate thermochemical data from density functional theory with ReaxFF minimal energy paths. We validate our models across different thermodynamic regimes, showing predictions of gas phase CO and NO concentrations and high-pressure induction times that are similar to experimental data. The kinetic models are analyzed to find fundamental decomposition reactions in different thermodynamic regimes.