Gas-phase Mechanism Research Articles

Exploring the Activation of Atomically Precise [Pt17(CO)12(PPh3)8]2+ Clusters: Mechanism and Energetics in Gas Phase and on an Inert Surface.

Atomically precise clusters such as [Pt17(CO)12(PPh3)8]x+ (x = 1,2) (PPh3 is triphenylphosphine) are known as precursors for making oxidation catalysts. However, the changes occurring to the cluster upon thermal activation during the formation of the active catalyst are poorly understood. We have used a combination of hybrid mass spectrometry and surface science to map the thermal decomposition of [Pt17(CO)12(PPh3)8](NO3)2. High-resolution mass and ion mobility spectrometry together with DFT-based modeling were used to probe the sequence of fragmentation reactions and fragment structures generated upon collisional excitation of [Pt17(CO)12(PPh3)8]2+. This was compared with thermal desorption spectroscopy of [Pt17(CO)12(PPh3)8](NO3)2 dropcast onto an inert graphite surface. In both cases, a characteristic sequence of CO and benzene desorption steps is observed followed at higher excitation energy by H2 loss. This behavior is indicative of Pt-catalyzed C-H activation of phenyl groups during partial stripping of the ligand shell while the Pt17P8 cluster core is retained.

Advances and Challenges in Speciation Measurement and Microkinetic Modeling for Gas-Solid Heterogeneous Catalysis.

Microkinetic modeling of heterogeneous catalysis serves as an efficient tool bridging atom-scale first-principles calculations and macroscale industrial reactor simulations. Fundamental understanding of the microkinetic mechanism relies on a combination of experimental and theoretical studies. This Perspective presents an overview of the latest progress of experimental and microkinetic modeling approaches applied to gas-solid catalytic kinetics. Then, opportunities and challenges are presented based on recent research progress in gas-solid catalysis and combustion chemistry. For experimental approaches, the importance of ideal catalytic reactors, structured catalysts, and precise elementary rate measurements is emphasized. Additionally, integrating spatiotemporally resolved operando gas-phase diagnostics with surface-adsorbed species characterization methods offers new opportunities for gaining deeper insights into gas-surface reactions. In microkinetic modeling, a hybrid rate parameter evaluation approach that combines first-principles calculations with semiempirical methods, followed by automated mechanism generation and data-driven optimization, opens new avenues for efficiently constructing surface mechanisms. Furthermore, extending microkinetic modeling beyond mean-field approximations allows simulations under realistic catalyst operating conditions. Finally, the critical role of gas-phase mechanisms and comprehensive microkinetic modeling analyses in advancing our fundamental understanding of gas-solid catalytic processes is highlighted.

Experimental and kinetic modeling study of oxidative degradation of benzene and phenol in supercritical water.

Benzene and phenol are representative aromatic compounds existing commonly in wastewater. The kinetics of oxidative degradation of benzene and phenol in supercritical water have been investigated in a flow reactor at 823K and 250atm, with the excess oxygen ratio ranging from 0.5 to 2.0. For supercritical water oxidation of benzene, CO2 was observed as the main product accounting for the largest fraction of the reacted carbon. Its concentration was higher than that of CO under all conditions, even at the initial reaction periods where benzene conversions were low. The phenol conversion was found to accelerate with increasing excess oxygen ratio, exhibiting strong dependence on oxygen concentration. CO2 and CO were the major gaseous products with comparable concentrations, and C2H2 was also formed in considerable amounts. A comprehensive chemical kinetic model was developed based on a gas-phase mechanism, and its performance was further validated by comparing to experimental data from different sources. The model reproduced the benzene and phenol conversions and CO concentration fairly well, but underpredicted the CO2 yield and overpredicted the C2H2 yield slightly. Reaction mechanisms were then inferred through kinetic analyses, emphasizing the importance of C6H5OO and C6H5O radicals. Finally, the kinetic characteristics of benzene and phenol oxidation in supercritical water and gas-phase environments were compared.

Unlocking the Mysteries of the Desorption-Ionization Mechanism via Separate Thermal and Charge Strategies.

Herein, a new strategy is employed to build a controllable thermal-coupled charge ionization (TCCI) device to elucidate the desorption-ionization mechanism of plasma ion sources. Efficient synergistic desorption and ionization are achieved within the TCCI device by independently controlling the desorption temperature and plasma charges. The TCCI device efficiently ionizes samples using abundant free electrons, charges, and active species from arc plasma. The coexistence of free electrons and hydroxide radicals confers redox capability to the TCCI system, implying the presence of a unified redox mechanism even when the arc plasma is transmitted through a metal conductor over a distance. In addition, molecular ions of the analytes facilitate the differentiation between primary and secondary amines during their analysis. Notably, the TCCI device enables a switch between hard and soft ionization by adjusting the thermal desorption temperature. At high temperatures (>400 °C), the TCCI device exhibits hard ionization characteristics, producing fragment ions beneficial for isomer discrimination. The TCCI mass spectrometry exhibits robust performance in terms of sensitivity and accuracy for detecting antibiotics and sterols in saline solutions, achieving linearity with correlation coefficients ≥0.99 and excellent reproducibility. The successful analysis of seven pharmaceuticals and four sterols in complex matrices using the TCCI device demonstrates its excellent salt and matrix tolerance. Overall, the TCCI device, with its independent control over thermal desorption and arc plasma, achieves efficient synergistic desorption and ionization, overcoming limitations in existing ionization technologies and contributing to the study of gas-phase ion dynamics and mechanisms.

A multizonal numerical combustion model of ammonium perchlorate

Solid rocket motors (SRM) are essential for national defense, satellite launch vehicles for placing spacecraft for communications, resource management, and space exploration. Numerical modeling of composite solid propellants is very helpful for optimizing performance, ensuring safety, and complementing experimental testing. It provides insights into combustion dynamics and allows for precise customization to meet specific mission needs, so modeling compositepropellants will stay important. AP (Ammonium Perchlorate), as a synthetic oxidizer, has been widely utilized in modern composite solid propellants. Therefore, it is crucial to understand the physicochemical processes such as condensed-phase heating and reaction kinetics, the interactions between the condensed and gas phases, and gas-phase combustion. A steady-state numerical simulation model is presented to study the combustion of AP. Zonal modeling is employed to treat the solid phase, melt layer, and gas phase separately with conservation of mass, energy, and species, and the solutions are coupled with appropriate boundary conditions. A simple global reaction is developed, validated, and used for the condensed phase with better surface species profiles than those available in the literature. A detailed reaction mechanism is used in the gas phase combustion. This model considers only liquid as a condensed phase and uses a newly condensed phase mechanism and a premixed AP/HTPB (hydroxyl-terminated polybutadiene) gas phase reaction mechanism instead of AP monopropellant gas phase mechanism. This modeling is a prerequisite for a more sophisticated multi-modal composite propellant model with AP grains and AP/HTPB binder. The predicted burn rate and initial temperature sensitivities for different motor operating pressures match well with experimental and other theoretical data. Also, the simulated melt layer thickness of the present model agrees well with experimental observations. Sensitivity analysis is performed for the melt temperature and activation energy for the condensed phase reaction. The simulation also predicts surface temperature and species profile with reasonable accuracy.

Novel packed-bed CFD model for pellet combustion: Validation and application to a stove

An advanced CFD (computational fluid dynamics) model has been developed to describe the combustion of wood pellets. It is based on a packed-bed approach and provides a realistic description of the combustion of pellets, resolved in 3D over the whole fuel bed. It considers the properties of the packed bed rather than the properties of the single fuel particles. Compared to a particle-based description, simulation times are shorter due to the reduced complexity. In the model, the local conditions in different parts of the fuel bed (temperatures, flow conditions, oxygen concentrations …) influence the various stages of the combustion process (drying, pyrolysis, charcoal gasification and combustion). The compaction of the fuel bed due to shrinkage of the fuel particles during conversion and the loss of the particle structure shortly before the conversion is complete are also included in the description. The formulation of the bed compaction, the radiation absorption model and the charcoal conversion reactions have been specifically tuned to the combustion of wood pellets. The detailed pyrolysis model includes not only the main components, but also higher hydrocarbon species and tars in a manner specific to the fuel considered. It has been combined with a chemical gas phase mechanism which is a reduction of a detailed mechanism developed for thermo-chemical biomass conversion. The model has been validated against measurement data from a lab-scale batch reactor, and then applied to simulate the fuel bed of a commercial pellet stove. The simulation results are in good agreement with the corresponding measurements.

Flame retarded lignin-based epoxy resin with excellent antibacterial and anti-corrosion properties modified by coordinated phospho-nitrogen flame retardant

In this paper, epoxidized lignin (HL) and sebacic acid (HSA) were used as the hard and soft segments, respectively, and a kind of reactive coordinated phosphorous-nitrogen flame retardants (DTZ) was designed and synthesized via Zn2+ coordination to fabricate a multifunctional non-bisphenol A lignin based epoxy (EP) composite. The swelling behavior and morphological analysis demonstrated that the crosslinking density of EP increased significantly after adding HL and DTZ. The existence of coordination sacrificial bond of DTZ dissipated more energy when it was subjected to external forces, thereby making 80HSA/14HL/6DTZ maintained a high tensile strength (10.65 MPa) while having little damage to the elongation at break (30.74 %). The limiting oxygen index (LOI) of 80HSA/14HL/6DTZ was significantly higher than that of 100HSA (22.3 %), reaching 36.6 %, and the vertical combustion test (UL-94) reached V-0 level. The morphology of carbon layer and residual carbon analysis showed that HL and DTZ had synergistic effect, and the flame retardancy mechanism of gas phase and condensed phase existed in the combustion process. Simultaneously, the addition of HL and DTZ also endowed the EP composite with excellent corrosion resistance and antibacterial properties.

Preparation and properties of phosphorus-containing thermotropic liquid crystal copolyester fibers with excellent flame retardance and mechanical property

In order to acquire polymeric fibers have both excellent flame retardance and mechanical properties, high molecular weight phosphorus-containing liquid crystal copolyesters derived from 6-hydroxy-2-naphthenic acid (HNA), terephthalic acid (TA) and 10-(2,5-dihydroxypheny)-10-hydro-9-oxa-10-phospha phenanthrene-10-oxide (DOPO-HQ) were synthesized via “one-pot” melt polymerization, and then the fibers were obtained by melt spinning method. The structure and property of the copolyesters were studied elaborately by experimental characterization technique and molecular simulation method. Shear shinning behavior was observed from rheology measurement, indicating that the copolyesters had excellent melt fluidity and spinnability. The rigidity of molecular chain was efficiently improved by the phosphorus-containing monomer DOPO-HQ and naphthalene HNA units which could be reflected by the molecular simulation results as well as high Tg values. The flame retardant mechanism of the phosphorus-containing flame retardant copolyester was systematically studied via limiting oxygen index (LOI), vertical burning (UL-94) test, cone calorimetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the copolyesters exhibit synergistic flame retardant mechanism of gas phase and condensed phase. Meanwhile, mechanical property of the as-spun fibers could be significantly improved by increasing the spinneret draw ratio (SDR) attributed to high molecular chain orientation. The maximum tensile strength of the as-spun fiber was 0.77 GPa observed for P-HNA60P20 at a relatively low SDR of 29. It was shown the unique combination of good thermal stability, spinnability as well as mechanical and flame retardant properties of the copolyesters would make them could be used as high-performance flame retardant materials.

Surface Fluorination of Nuclear Graphite Exposed to Molten 2LiF-BeF2 (FLiBe) Salt and Its Cover Gas at 700 °C.

This study demonstrates that the reaction of Li2BeF4 (FLiBe) with graphite both in the liquid phase and the gas phase of the molten salt leads to the formation of covalent and semi-ionic carbon-fluorine bonds at the graphite surface and is accompanied by surface microstructural changes, removal of C-O groups, and deposition of metallic beryllium, based on XPS, Raman, and glow discharge mass spectroscopy characterization. At 700 °C, the observed surface density of C-F is higher after 240 h than after 12 h of exposure to molten FLiBe salt; the kinetics of covalent C-F formation is slower than that of semi-ionic C-F formation, and the relative amount of semi-ionic C-F content increases with depth. The graphite sample exposed to the cover gas exhibits less surface fluorination than the salt-exposed sample, with predominantly semi-ionic C-F. Based on these observations and the observed LiF/BeF2 ratio by surface XPS, the hypotheses that fluorination of the salt-exposed graphite occurs via a gas-phase mechanism or that it requires salt intrusion are refuted; future studies are warranted on the transport of C-F semi-ionic and covalent species in graphite at high temperatures.

Eco-friendly, efficient and durable flame retardant lyocell fabrics prepared via a feasible grafting of taurine

Inspired by alkaline oxidative degradation of cellulose, a novel eco-friendly scenario for preparation of flame retardant lyocell fabrics was developed by the chemical grafting of biomass taurine. FTIR and XPS results verified the establishment of a covalent bond between taurine and lyocell fabric. Thermogravimetric analysis and vertical combustion test proved the improved char-forming ability and flame resistance of the grafted fabric. The THR and pHRR of the finished fabric were successfully reduced by 67.3 % and 89.9 % respectively after modification. In addition, after 50 wash cycles, the LOI value of the grafted fabric was maintained at 29.5 %. The gas-phase and condensed-phase flame retardant mechanisms were proposed from the analyses of pyrolysis gaseous products and char residue of the modified fabrics. The modification process is simple to operate and provides a feasible green flame retardant strategy for flammable lyocell fabrics.

Combustion Characteristics of Sinusoidal-Shaped Walls with Catalyst Segmentation in Micro-Combustors for Micro-Thermophotovoltaic Application

The combustion characteristics of micro-combustors significantly impact the performance of micro-thermophotovoltaic (MTPV) systems. This study aims to investigate the effects of sinusoidal-shaped walls and catalyst segmentation on flame stability and combustion performance in a micro-combustor by using numerical methods. The numerical simulation with detailed gas-phase and surface reaction mechanisms is reliable, as the results of numerical simulation align with experimental data. The results show that the interplay between flame stability and sinusoidal-shaped walls is crucial, particularly because of the cavities formed by the sinusoidal-shaped walls of the micro-combustor. The gas-phase ignition position of the sinusoidal-shaped wall combustor moves upstream by 0.050 m compared to the planar-wall combustor, but the flame is stretched. The catalyst segments coated on the crest can shorten the flame length and increase the average temperature by a maximum 62 K, but delay the gas-phase ignition. Conversely, catalyst segments coated on the trough can advance ignition, but this results in flame elongation and a decrease in the average temperature. The rational combination of catalyst segmentation and sinusoidal-shaped walls facilitates moving the ignition position upstream by a maximum of 0.065 m while substantially reducing the length of the combustor required for complete fuel conversion by more than 60%. These attributes are highly beneficial for improving efficiency and minimizing the length of the micro-combustor for MTPV application.

Core-shell flame retardant/APP-PEI@MXene@ZIF-67: A nanomaterials self-assembly strategy towards reducing fire hazard of thermoplastic polyurethane

Ammonium polyphosphate (APP) is the most commercially valuable phosphorus-based flame retardant, but poor interaction with the polymer interface limits the flame-retardant efficiency. In this work, a new type of multi-layered nanomaterial coating APP (APP-PEI@MXene@ZIF-67) was prepared and introduced into thermoplastic polyurethane (TPU) polymers by a simple and green assembly strategy. The effects of different loading shells of modified APP on the flame retardancy of TPU composites were investigated, as well as their gas/condensed phase thermal degradation products and their flame-retardant mechanisms. The results showed that APP-PEI@MXene@ZIF-67 was more favorable for catalytic char formation than APP, and the residual char formed by its composites was denser and more continuous. Compared with the pure TPU, the pHRR, THR, pSPR, and TSP of TPU/APP-PEI@MXene@ZIF-67–2BL composites were decreased by 72.75 %, 87.25 %, 59.58 %, and 85.97 %, respectively, which significantly reduced the heat and smoke release during the combustion process. The gas-phase and condensed-phase flame retardant mechanisms synergized to construct a possible approach to address the fire risk and heat/smoke hazards of TPUs and promote the extensive application of TPU polymers.

Evaluating the sensitivity of fine particulate matter (PM2.5) simulations to chemical mechanism in WRF-Chem over Delhi

Accurate prediction of PM2.5, its optical properties and dominant chemical components are essential for air quality studies. In this study, we investigated the effects of two gas phase chemical schemes coupled with three aerosol mechanisms on the simulated PM2.5 mass concentration in Delhi using the Weather Research and Forecasting model with Chemistry module (WRF-Chem). The model was employed to cover the entire northern region of India at 10 km horizontal spacing and results were compared with comprehensive field data set on dominant PM2.5 chemical compounds from the Winter Fog EXperiment (WiFEX) at the Indira-Gandhi International Airport, New Delhi, and surface PM2.5 observations in Delhi (17 sites), Punjab (3 sites), Haryana (4 sites), Uttar Pradesh (7 sites) and Rajasthan (17 sites). The Model for Ozone and related Chemical Tracers (MOZART) gas-phase chemical mechanism coupled with the Goddard Chemistry Aerosol Radiation and Transport (GOCART) aerosol scheme were selected in the first experiment as it is currently employed in the operational air quality forecasting system of Ministry of Earth Sciences (MoES), Government of India. Other two simulations were performed with the MOZART gas phase chemical mechanism coupled with the Model for Simulating Aerosol Interactions and Chemistry (MOZART-MOSAIC), and Carbon Bond 5 (CB-05) gas mechanism coupled with the Modal Aerosol Dynamics Model for Europe/Secondary Organic Aerosol Model (CB05 - MADE/SORGAM) aerosol mechanisms. The evaluation demonstrated that chemical mechanisms affect the evolution of gas-phase precursors and aerosol processes which in turn affect the optical depth and overall performance of the model for PM2.5. All the three chemical schemes underestimate the observed concentrations of major aerosol composition and precursor gases over Delhi. Comparison with observations suggests that, the simulations using MOZART gas-phase chemical mechanism with MOSAIC aerosol scheme performed better in simulating aerosols over Delhi and its optical depth over the IGP.

The gas phase mechanism process of TiCl4 oxidation to rutile TiO2 and the inhibition of KCl on crystal nucleation

This paper studied the microscopic mechanism of the gas phase nucleation reaction during the TiCl4 oxidation‒reduction reaction and the inhibition effect of the nucleation inhibitor KCl on TiO2 nucleation. The optimal pathway for TiO2 nucleation was identified as TiCl3 + Ti2O2Cl5 → TiCl4 + Ti2O2Cl4, achieved through calculation and optimization of the transition state, coupled with an analysis of the reaction energy barriers and their respective pathways. The cluster structure model of (TiO2)n (where n = 1∼7) and its stable configuration were optimized. For clusters where n = 1–2, the B3LYP functional provides a more accurate calculation of the excited state energy. Conversely, the PW91 functional demonstrates higher accuracy for larger clusters, indicative of a stronger coupling effect between the electronic state and atomic nucleus vibration in the system. Comparing the change trend of the bond length of O2c, O3c and Ti5c, shows that the optimal site of K+ adsorption on the rutile TiO2 (110) surface is O2c. Based on this, the adsorption mechanism of TiCl4 molecules on a complete rutile type TiO2 (110) surface containing one oxygen defect and two oxygen defects was studied. The results shows the adsorption energy increases, and the adsorption structure is unstable with oxygen defects.

Detailed kinetic modeling of catalytic oxidative coupling of methane

The oxidative coupling of methane (OCM) at high temperature over monolithic Pt-based catalysts operated at short contact times is investigated as an attractive method for methane upgrading to higher value products like ethylene and acetylene. An experimental measurement campaign aiming at elucidating the effect of operation parameters on the catalyst performance revealed that lower N2 dilution, lower CH4/O2 ratio, and higher space velocities promote high C2 yields. A maximum C2 yield of 10 % with 94 % CH4 conversion was obtained at a CH4/O2 ratio of 1.1, 50 % N2 dilution, and a space velocity of 4.5 × 105 h−1. Since both heterogenous and homogenous gas-phase chemistry together are required for determining C2 formation pathways, a detailed OCM surface reaction mechanism over Pt is presented consisting of 26 species and 86 reactions that are consistent from the view of thermodynamics and micro-kinetic reversibility. The combination of this OCM surface mechanism with a detailed gas-phase mechanism allows a numerical micro-kinetic description of the experimental measurements. The simulations presented in this study suggest that C2 formation takes place in the gas-phase at temperature above 1200 K with both oxidative and pyrolytic pathways for methane dehydrogenation to form CH3 radicals, whose coupling results in C2H6, C2H4 and C2H2 formation. Furthermore, the simultaneous presence of sufficient oxygen content and heat are vital for high C2 species yields.

Numerical investigation on pyrolysis and ignition of ammonia/coal blends during co-firing

Co-firing ammonia with coal is a promising and feasible technology for reducing coal-related carbon emissions. Pyrolysis and ignition of ammonia-coal blended fuels are the key steps for flame stability and boiler operation safety throughout the conversion process but remain unclear. In this work, an extended Euler–Lagrange framework coupled to detailed solid-phase pyrolysis kinetics and gas-phase reactions mechanism is introduced and validated against experimental results for ammonia-coal co-firing in a two-stage flat flame burner. First, the CRECK-S coal pyrolysis model was validated with TGA experiments and the CPD model at different heating rates to determine parameters for a competing two-step model for CFD simulations. Second, a detailed gas-phase mechanism with 116 species and 1513 elementary reactions was derived from the volatile and ammonia reaction mechanisms. Thirdly, the co-firing simulations were validated for the ignition delay time for various ammonia co-firing ratios. The results show that increasing the co-firing ratios from 0.0 to 1.0 results in gradually increasing ignition delay times in a low-oxygen atmosphere. Further analysis demonstrates that adding ammonia accelerates the coal particle heating rate due to the reduced coal particle number density and ammonia reaction induced gas-phase temperature increase, and thus the coal devolatilization rate is increased. The latter plays a dominant role. Hydrogen produced from ammonia pyrolysis is negligible, so ammonia predominantly participates in the ignition. Time scale analysis shows that homogeneous ignition is dominant during the ignition process. The presence of ammonia inhibits the inward oxygen diffusion and causes the reaction zone to move away from the pulverized coal particle flow. The oxygen diffusion inhibition and low reactivity of ammonia compared to volatiles lead to an increase in ignition delay time for ammonia co-firing, even though pulverized coal devolatilization is accelerated.

Urban and Remote cheMistry modELLing with the new chemical mechanism URMELL: part I gas-phase mechanism development

URMELL, the new gas-phase chemical mechanism for Urban and Remote cheMistry modELLing with a comprehensive isoprene and aromatics chemistry scheme. URMELL includes various highly oxidized molecules which enable a direct and explicit SOA treatment.

Experimental Study on the Isolation Effect of an Active Flame-Proof Device on a Gas Explosion in an Underground Coal Mine

Passive explosion-isolation facilities in underground coal mines, such as explosion-proof water troughs and bags, face challenges aligned with current trends in intelligent and unmanned technologies, due to restricted applicability and structural features. Grounded in the propagation laws and disaster mechanisms of gas explosions, the device in this paper enables accurate identification of explosion flames and pressure information. Utilizing a high-speed processor for rapid logical processing enables judgments within 1 ms. Graded activation of the operating mechanism is enabled by the device. The tunnel flame-proof device’s flame-extinguishing agent has a continuous action time of 6075 ms. Experiments on the active flame-proof effect of a 100 m3 gas explosion were conducted using a cross-sectional 7.2 m2 large-tunnel test system. With a dosage of 5.6 kg/m2, the powder flame-extinguishing agent completely extinguished the explosion flame within a 20 m range behind the explosion isolator. Numerical calculations unveiled the gas-phase chemical suppression mechanism of the powder flame-extinguishing agent NH4H2PO4 in suppressing methane explosions. Building upon these findings, application technology for active flame-proofing was developed, offering technical support for intelligent prevention and control of gas explosions in underground coal mines.

Gas-Phase vs. Grain-Surface Formation of Interstellar Complex Organic Molecules: A Comprehensive Quantum-Chemical Study

Several organic chemical compounds (the so-called interstellar complex organic molecules, iCOMs) have been identified in the interstellar medium (ISM). Examples of iCOMs are formamide (HCONH2), acetaldehyde (CH3CHO), methyl formate (CH3OCHO), or formic acid (HCOOH). iCOMs can serve as precursors of other organic molecules of enhanced complexity, and hence they are key species in chemical evolution in the ISM. The formation of iCOMs is still a subject of a vivid debate, in which gas-phase or grain-surface syntheses have been postulated. In this study, we investigate the grain-surface-formation pathways for the four above-mentioned iCOMs by transferring their primary gas-phase synthetic routes onto water ice surfaces. Our objective is twofold: (i) to identify potential grain-surface-reaction mechanisms leading to the formation of these iCOMs, and (ii) to decipher either parallelisms or disparities between the gas-phase and the grain-surface reactions. Results obtained indicate that the presence of the icy surface modifies the energetic features of the reactions compared to the gas-phase scenario, by increasing some of the energy barriers. Therefore, the investigated gas-phase mechanisms seem unlikely to occur on the icy grains, highlighting the distinctiveness between the gas-phase and the grain-surface chemistry.

Implementation of a parallel reduction algorithm in the GENerator of reduced Organic Aerosol mechanisms (GENOA v2.0): Application to multiple monoterpene aerosol precursors

Explicit gas-phase chemical mechanisms represent the state of knowledge regarding the chemistry of volatile organic compounds (VOCs), which are crucial in the formation of secondary organic aerosols (SOAs). However, these chemical mechanisms are computationally expensive, which limits their practical use in large-scale air quality modeling. Mechanism reduction is therefore required for computational efficiency while preserving the accuracy of the detailed gas-phase chemical mechanisms.This paper presents a new version of the Generator of Reduced Organic Aerosol Mechanisms (GENOA v2.0), which reduces mechanisms at a size suitable for three-dimensional (3-D) modeling while preserving the accuracy of detailed chemical mechanisms for simulating aerosol concentrations. GENOA v2.0 adopts a parallel reduction framework to identify the most optimal reductions from competitive candidates, and can reduce chemical mechanisms from multiple aerosol precursors. To demonstrate the reduction efficiency, GENOA v2.0 is applied to the reduction of monoterpene chemistry from the Master Chemical Mechanism (MCM) combined with the Peroxy Radical Autoxidation Mechanism (PRAM) mechanism. The original mechanism, consisting of 3 001 reactions and 1 227 species (including 738 condensable species), is reduced by 93% to 197 reactions and 110 species (including 23 condensable species), inducing an average error of only 3% in aerosol concentrations. Sensitivity tests showed that this reduced mechanism behaved similarly to the original mechanism in response to changes in environmental conditions such as temperature, relative humidity, and SOA mass loading. Moreover, if the error tolerance is increased to 20% — which can still be acceptable for 3-D air quality modeling — the mechanism can be further simplified to 40 reactions and 24 species (including 5 condensable species). Consequently, the GENOA-generated aerosol mechanism preserves the complexity of the detailed gas-phase chemical mechanisms on SOA formation while increasing computational efficiency, which makes it suitable for most environmental conditions encountered in the atmosphere.