Structural Effects of Amines in Enhancing Methanesulfonic Acid-Driven New Particle Formation

Enhancement of atmospheric nucleation precursors on formic sulfuric anhydride induced nucleation: Theoretical mechanism

As an intermediate formed by H2SO4 (SA), formic sulfate anhydride (FSA) has been hypothesized to play a role in the nucleation of atmospheric aerosols. It is the first time that the clusters (SA)x(A)y(W)n and (FSA)x(A)y(W)n (x = 1-2; y = 1-2; n = 0-4) were systematically studied in theory on the structures, thermodynamics, intermolecular interactions, humidity dependence, atmospheric dependence and optical properties. FSA is predicted to be more stronger to promote the clustering with ammonia (A) than SA, suggesting that substituent group enhances nucleation capability of FSA. Whereas, the substituent group does not influence the humidity sensitivity of hydrated clusters. The clusters trend to form small hydrated clusters (nwater≦3). The study on atmospheric dependence indicates that the stability of the clusters depends more on temperature other than pressure. Moreover, FSA shows a stronger ability on reducing atmospheric visibility than A, SA and water molecules. This finding aims to draw attention to FSA about atmospheric nucleation.

Insights into the role of the H-abstraction reaction kinetics of amines in understanding their degeneration fates under atmospheric and combustion conditions

Amines, a class of prototypical volatile organic compounds, have garnered considerable interest within the context of atmospheric and combustion chemistry due to their substantial contributions to the formation of hazardous pollutants in the atmosphere. In the current energy landscape, the implementation of carbon-neutral energy and strategic initiatives leads to generation of new amine sources that cannot be overlooked in terms of the emission scale. To reduce the emission level of amines from their sources and mitigate their impact on the formation of harmful substances, a comprehensive understanding of the fundamental reaction kinetics during the degeneration process of amines is imperative. This perspective article first presents an overview of both traditional amine sources and emerging amine sources within the context of carbon peaking and carbon neutrality and then highlights the importance of H-abstraction reactions in understanding the atmospheric and combustion chemistry of amines from the perspective of reaction kinetics. Subsequently, the current experimental and theoretical techniques for investigating the H-abstraction reactions of amines are introduced, and a concise summary of research endeavors made in this field over the past few decades is provided. In order to provide accurate kinetic parameters of the H-abstraction reactions of amines, advanced kinetic calculations are performed using the multi-path canonical variational theory combined with the small-curvature tunneling and specific-reaction parameter methods. By comparing with the literature data, current kinetic calculations are comprehensively evaluated, and these validated data are valuable for the development of the reaction mechanism of amines.

Implications for new particle formation in air of the use of monoethanolamine in carbon capture and storage

Alkanolamines are currently being deployed in carbon capture and storage (CCS) technology worldwide, and atmospheric emissions have been found to coincide with locations exhibiting elevated concentrations of methanesulfonic acid (MSA). It is thus critical to understand the fate and potential atmospheric reactions of these chemicals. This study reports the characterization of sub-10 nm nanoparticles produced through the acid-base reaction between gas phase monoethanolamine (MEA) and MSA, a product of organosulfur compound oxidation in air, using a flow reactor under dry and humid (up to ∼60% RH) conditions. Number size distribution measurements show that MEA is even more efficient than methylamine in forming nanoparticles on reaction with MSA. This is attributed to the fact that the MEA structure contains both an -NH2 and an -OH group that facilitate hydrogen bonding within the clusters, in addition to the electrostatic interactions. Due to this already strong H-bond network, water has a relatively small influence on new particle formation (NPF) and growth in this system, in contrast to MSA reactions with alkylamines. Acid/base molar ratios of unity for 4-12 nm particles were measured using thermal desorption chemical ionization mass spectrometry. The data indicate that reaction of MEA with MSA may dominate NPF under some atmospheric conditions. Thus, the unique characteristics of alkanolamines in NPF must be taken into account for accurate predictions of impacts of CCS on visibility, health and climate.

HIO3-HIO2-Driven Three-Component Nucleation: Screening Model and Cluster Formation Mechanism

Iodine oxoacids (HIO3 and HIO2)-driven nucleation has been suggested to efficiently contribute to new particle formation (NPF) in marine atmospheres. Abundant atmospheric nucleation precursors may further enhance HIO3-HIO2-driven nucleation through various multicomponent nucleation mechanisms. However, the specific enhancing potential (EP) of different precursors remains largely unknown. Herein, the EP-based screening model of precursors and enhancing mechanism of the precursor with the highest EP on HIO3-HIO2 nucleation were investigated. The formation free energies (ΔG), as critical parameters for evaluating EP, were calculated for the dimers of 63 selected precursors with HIO2. Based on the ΔG values, (1) a quantitative structure-activity relationship model was developed for evaluating ΔG of other precursors and (2) atmospheric concentrations of 63 (precursor)1(HIO2)1 dimer clusters were assessed to identify the precursors with the highest EP for HIO3-HIO2-driven nucleation by combining with earlier results for the nucleation with HIO3 as the partner. Methanesulfonic acid (MSA) was found to be one of the precursors with the highest EP. Finally, we found that MSA can effectively enhance HIO3-HIO2 nucleation at atmospheric conditions by studying larger MSA-HIO3-HIO2 clusters. These results augment our current understanding of HIO3-HIO2 and MSA-driven nucleation and may suggest a larger impact of HIO2 in atmospheric aerosol nucleation.

Methanesulfonic acid and iodous acid nucleation: a novel mechanism for marine aerosols

By seeding clouds, new particle formation (NPF) has a substantial impact on radiation balance, bio-geochemical cycles and global climate. Over oceans, both methanesulfonic acid (CH₃S(O)₂OH, MSA) and iodous acid (HIO₂) have been reported to be closely associated with NPF events; however, much less is known about whether they can jointly nucleate to form nanoclusters. Hence, quantum chemical calculations and Atmospheric Cluster Dynamics Code (ACDC) simulations were performed to investigate the novel mechanism of MSA-HIO₂ binary nucleation. The results indicate that MSA and HIO₂ can form stable clusters via multiple interactions including hydrogen bonds, halogen bonds, and electrostatic forces between ion pairs after proton transfer, which are more diverse than those in MSA-iodic acid (HIO₃) and MSA-dimethylamine (DMA) clusters. Interestingly, HIO₂ can be protonated by MSA exhibiting base-like behavior, but it differs from base nucleation precursors by self-nucleation rather than solely binding to MSA. Due to the greater stability of MSA-HIO₂ clusters, the formation rate of MSA-HIO₂ clusters can be even higher than that of MSA-DMA clusters, suggesting that MSA-HIO₂ nucleation is a non-negligible source of marine NPF. This work proposes a novel mechanism of MSA-HIO₂ binary nucleation for marine aerosols and provides deeper insights into the distinctive nucleation characteristics of HIO₂, which can help in constructing a more comprehensive sulfur- and iodine-bearing nucleation model for marine NPF.

Enhancement of Atmospheric Nucleation Precursors on Iodic Acid-Induced Nucleation: Predictive Model and Mechanism

Iodic acid (IA) has recently been recognized as a key driver for new particle formation (NPF) in marine atmospheres. However, the knowledge of which atmospheric vapors can enhance IA-induced NPF remains limited. The unique halogen bond (XB)-forming capacity of IA makes it difficult to evaluate the enhancing potential (EP) of target compounds on IA-induced NPF based on widely studied sulfuric acid systems. Herein, we employed a three-step procedure to evaluate the EP of potential atmospheric nucleation precursors on IA-induced NPF. First, we evaluated the EP of 63 precursors by simulating the formation free energies (ΔG) of the IA-containing dimer clusters. Among all dimer clusters, 44 contained XBs, demonstrating that XBs are frequently formed. Based on the calculated ΔG values, a quantitative structure-activity relationship model was developed for evaluating the EP of other precursors. Second, amines and O/S-atom-containing acids were found to have high EP, with diethylamine (DEA) yielding the highest potential to enhance IA-induced nucleation by combining both the calculated ΔG and atmospheric concentration of considered 63 precursors. Finally, by studying larger (IA)_1-3(DEA)_1-3 clusters, we found that the IA-DEA system with merely 0.1 ppt (2.5×10⁶ cm^-3) DEA yields comparable nucleation rates to that of the IA-iodous acid system.

Molecular Insights into Cyclodextrin-Adamantane-Modified Copolymer Host-Guest Interactions

Supramolecular polymer flooding has great potential in solving the problems of difficult injection and low recovery in low-permeability polymer reservoirs. However, the self-assembly mechanism of supramolecular polymers is not yet to be fully understood at the molecular level. In this work, molecular dynamics simulations were used to explore the formation of cyclodextrin and adamantane-modified supramolecular polymer hydrogels; the self-assembly mechanism was summarized; and the effect of concentration on the oil displacement index was evaluated. The assembly mechanism of supramolecular polymers can be attributed to the "node-rebar-cement" mode of action. At the same time, Na⁺ can form intermolecular and intramolecular salt bridges with supramolecular polymers, and together with the "node-rebar-cement" mode of action, the supramolecular polymers can form a more compact 3D network structure. When the polymer concentration was increased, especially up to its critical association concentration (CAC), the association increased significantly. Besides, the construction of a 3D network was promoted, which results in a higher viscosity. This work investigated the assembly process of supramolecular polymers from the molecular scale and explained its mechanism of action, which makes up for the deficiencies of other research methods and provides a theoretical basis for screening out functional units that can be used for the supramolecular polymer assembly.

Clusteromics V: Organic Enhanced Atmospheric Cluster Formation

Formic acid (FA) is a prominent candidate for organic enhanced nucleation due to its high abundance and stabilizing effect on smaller clusters. Its role in new particle formation is studied through the use of state-of-the-art quantum chemical methods on the cluster systems (acid)_1-2(FA)₁(base)_1-2 with the acids being sulfuric acid (SA)/methanesulfonic acid (MSA) and the bases consisting of ammonia (A), methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), and ethylenediamine (EDA). A funneling approach is used to determine the cluster structures with initial configurations generated through the ABCluster program, followed by semiempirical PM7 and ωB97X-D/6-31++G(d,p) calculations. The final binding free energy is calculated at the DLPNO-CCSD(T₀)/aug-cc-pVTZ//ωB97X-D/6-31++G(d,p) level of theory using the quasi-harmonic approximation. Cluster dynamics simulations show that FA has a minuscule or negligible effect on the MSA-FA-base systems as well as most of the SA-FA-base systems. The SA-FA-DMA cluster system shows the highest influence from FA with an enhancement of 21%, compared to its non-FA counterpart.

Formation mechanism of typical aromatic sulfuric anhydrides and their potential role in atmospheric nucleation process

Sulfuric anhydrides, generated from the cycloaddition reaction of SO₃ with carboxylic acids, have been revealed to be potential participants in the nucleation process of new particle formation (NPF). Hence the reaction mechanisms of typical aromatic acids (benzoic acid (BA), phenylacetic acid (PAA), phthalic acid (PA), isophthalic acid (mPA), and terephthalic acid (PTA)) with SO₃ to generate the corresponding aromatic sulfuric anhydrides were investigated by density functional theory calculations at the level of M06-2X/6-311++G(3df,3pd). As a result, these reactions were found to be feasible in the gas phase with barriers of 0.34, 0.30, 0.18, 0.08 and 0.12 kcal/mol to generate corresponding aromatic sulfuric anhydrides, respectively. The thermodynamic stabilities of clusters containing aromatic sulfuric anhydrides and atmospheric nucleation precursors (sulfuric acid, ammonia and dimethylamine) were further analyzed to identify the potential role of aromatic sulfuric anhydrides in NPF. As the thermodynamic stability of a cluster depends on both the number and strength of hydrogen bonds, the greater stability of the interactions between atmospheric nucleation precursors and aromatic sulfuric anhydrides than with aromatic acids make aromatic sulfuric anhydrides potential participators in the nucleation process of NPF. Moreover, compared with BA, the addition of a -CH₂- functional group in PAA has little influence on the reaction barrier with SO₃ but an inhibitive effect on the thermodynamic stability of clusters. The position of the two -COOH functional groups in PA, mPA and PTA does not have a consistent impact on the reaction barrier with SO₃ or the thermodynamic stability.

Computational chemistry of cluster: Understanding the mechanism of atmospheric new particle formation at the molecular level

New particle formation (NPF), which exerts significant influence over human health and global climate, has been a hot topic and rapidly expands field of research in the environmental and atmospheric chemistry recent years. Generally, NPF contains two processes: formation of critical nucleus and further growth of the nucleus. However, due to the complexity of the atmospheric nucleation, which is a multicomponent process, formation of critical clusters as well as their growth is still connected to large uncertainties. Detection limits of instruments in measuring specific gaseous aerosol precursors and chemical compositions at the molecular level call for computational studies. Computational chemistry could effectively compensate the deficiency of laboratory experiments as well as observations and predict the nucleation mechanisms. We review the present theoretical literatures that discuss nucleation mechanism of atmospheric clusters. Focus of this review is on different nucleation systems involving sulfur-containing species, nitrogen-containing species and iodine-containing species. We hope this review will provide a deep insight for the molecular interaction of nucleation precursors and reveal nucleation mechanism at the molecular level.

Critical Role of Iodous Acid in Neutral Iodine Oxoacid Nucleation

Nucleation of neutral iodine particles has recently been found to involve both iodic acid (HIO₃) and iodous acid (HIO₂). However, the precise role of HIO₂ in iodine oxoacid nucleation remains unclear. Herein, we probe such a role by investigating the cluster formation mechanisms and kinetics of (HIO₃)_m(HIO₂)_n (m = 0-4, n = 0-4) clusters with quantum chemical calculations and atmospheric cluster dynamics modeling. When compared with HIO₃, we find that HIO₂ binds more strongly with HIO₃ and also more strongly with HIO₂. After accounting for ambient vapor concentrations, the fastest nucleation rate is predicted for mixed HIO₃-HIO₂ clusters rather than for pure HIO₃ or HIO₂ ones. Our calculations reveal that the strong binding results from HIO₂ exhibiting a base behavior (accepting a proton from HIO₃) and forming stronger halogen bonds. Moreover, the binding energies of (HIO₃)_m(HIO₂)_n clusters show a far more tolerant choice of growth paths when compared with the strict stoichiometry required for sulfuric acid-base nucleation. Our predicted cluster formation rates and dimer concentrations are acceptably consistent with those measured by the Cosmic Leaving Outdoor Droplets (CLOUD) experiment. This study suggests that HIO₂ could facilitate the nucleation of other acids beyond HIO₃ in regions where base vapors such as ammonia or amines are scarce.

Contribution of Methanesulfonic Acid to the Formation of Molecular Clusters in the Marine Atmosphere

Because of the lack of long-term measurements, new particle formation (NPF) in the marine atmosphere remains puzzling. Using quantum chemical methods, this study elucidates the cluster formation and further growth of sulfuric acid-methanesulfonic acid-dimethylamine (SA-MSA-DMA) clusters, relevant to NPF in the marine atmosphere. The cluster structures and thermochemical parameters of (SA)_n(MSA)_m(DMA)_l (n + m ≤ 4 and l ≤ 4) systems are calculated using density functional theory at the ωB97X-D/6-31++G(d,p) level of theory, and the single-point energies are calculated using high-level DLPNO-CCSD(T₀)/aug-cc-pVTZ calculations. The calculated thermochemistry is used as input to the Atmospheric Cluster Dynamics Code (ACDC) to gain insight into the cluster dynamics. At ambient conditions (298.15 K, 1 atm), we find that the distribution of outgrowing clusters primarily consists of SA and DMA, with a minor contribution from the mixed SA-MSA-DMA clusters. At lower temperature (278.15 K, 1 atm) the distribution broadens, and clusters containing one or more MSA molecules emerge. These findings show that in the cold marine atmosphere MSA likely participates in atmospheric NPF.

Clusteromics IV: The Role of Nitric Acid in Atmospheric Cluster Formation

Nitric acid (NA) has previously been shown to affect atmospheric new particle formation; however, its role still remains highly uncertain. Through the employment of state-of-the-art quantum chemical methods, we study the (acid)_1-2(base)_1-2 and (acid)₃(base)₂ clusters containing at least one nitric acid (NA) and sulfuric acid (SA) or methanesulfonic acid (MSA) with bases ammonia (A), methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), and ethylenediamine (EDA). The initial cluster configurations are generated using the ABCluster program. PM7 and ωB97X-D/6-31++G(d,p) calculations are used to reduce the number of relevant configurations. The thermochemical parameters are calculated at the ωB97X-D/6-31++G(d,p) level of theory with the quasi-harmonic approximation, and the final single-point energies are calculated with high-level DLPNO-CCSD(T₀)/aug-cc-pVTZ calculations. The enhancing effect from the presence of nitric acid on cluster formation is studied using the calculated thermochemical data and cluster dynamics simulations. We find that when NA is in excess compared with the other acids, it has a substantial enhancing effect on the cluster formation potential.

Amine-Enhanced Methanesulfonic Acid-Driven Nucleation: Predictive Model and Cluster Formation Mechanism

Atmospheric amines are considered to be an effective enhancer for methanesulfonic acid (MSA)-driven nucleation. However, out of the 195 detected atmospheric amines, the enhancing potential (EP) has so far only been studied for five amines. This severely hinders the understanding of the contribution of amines to MSA-driven nucleation. Herein, a two-step procedure was employed to probe the EP of various amines on MSA-driven nucleation. Initially, the formation free energies (ΔG) of 50 MSA-amine dimer clusters were calculated. Based on the calculated ΔG values, a robust quantitative structure-activity relationship (QSAR) model was built and utilized to predict the ΔG values of the remaining 145 amines. The QSAR model identified two guanidino-containing compounds as the potentially strongest enhancer for MSA-driven nucleation. Second, the EP of guanidino-containing compounds was studied by employing larger clusters and selecting guanidine (Gud) as a representative. The results indicate that Gud indeed has the strongest EP. The Gud-MSA system presents a unique clustering mechanism, proceeding via the initial formation of the (Gud)₁(MSA)₁ cluster, and subsequently by cluster collisions with either a (Gud)₁(MSA)₁ or (Gud)₂(MSA)₂ cluster. The developed QSAR model and the identification of amines with the strongest EP provide a foundation for comprehensively evaluating the contribution of atmospheric amines to MSA-driven nucleation.

Contribution of reaction of atmospheric amine with sulfuric acid to mixing particle formation from clay mineral

During dust storm, mineral particle is frequently observed to be mixed with anthropogenic pollutants (APs) and forms mixing particle which arises more complex influences on regional climate than unmixed mineral particle. Even though mixing particle formation mechanism received significant attention recently, most studies focused on the heterogeneous reaction of inorganic APs on single composition of mineral. Here, the heterogeneous reaction mechanism of amine (a proxy of organic APs) with sulfuric acid (SA) on kaolinite (Kao, a proxy of mineral dust), and its contribution to mixing particle formation are investigated under variable atmospheric conditions. Two heterogeneous reactions of Kao-SA-amine and Kao-H₂O-SA-amine in absence/presence of water were comparably investigated using combined theoretical and experimental methods, respectively. The contribution from such two heterogeneous reactions to mixing particle formation was evaluated, respectively, exploring the effect of methyl groups (1-3 -CH₃), relative humidity (RH) (11-100%) and temperature (220-298.15 K). Water was observed to play a significant role in promoting heterogeneous reaction of amines with SA on Kao surface, reducing formation energy of mixing particle containing ammonium salt converted by SA. Moreover, the promotion effect from water is enhanced with the increasing RH and the decreasing temperature. For methylamine and dimethylamine containing 1-2 -CH₃, the heterogeneous reaction of Kao-H₂O-SA-amine contributes more to mixing particle formation. However, for trimethylamine containing 3 -CH₃, the heterogeneous reaction of Kao-SA-amine is the dominant source to mixing particle formation. For mixing particle generated from the above two heterogeneous reactions, ammoniums salts are supposed to be predominant components which is of strong hygroscopicity and further leads to significant influence on climate by altering radiative forcing of mixed particle and participating in the cloud condensation nuclei and ice nuclei.

Clusteromics III: Acid Synergy in Sulfuric Acid-Methanesulfonic Acid-Base Cluster Formation

Acid-base molecular clusters are an important stage in atmospheric new particle formation. While such clusters are most likely multicomponent in nature, there are very few reports on clusters consisting of multiple acid molecules and multiple base molecules. By applying state-of-the-art quantum chemical methods, we herein study electrically neutral (SA)₁(MSA)₁(base)_0-2 clusters with base = ammonia (A), methylamine (MA), dimethylamine (DMA), trimethylamine (TMA) and ethylenediamine (EDA). The cluster structures are obtained using a funneling approach employing the ABCluster program, semiempirical PM7 calculations and ωB97X-D/6-31++G(d,p) calculations. The final binding free energies are calculated at the DLPNO-CCSD(T₀)/aug-cc-pVTZ//ωB97X-D/6-31++G(d,p) level of theory using the quasi-harmonic approximation. Based on the calculated cluster geometries and thermochemistry (at 298.15 K and 1 atm), we find that the mixed (SA)₁(MSA)₁(base)_1-2 clusters more resemble the (SA)₂(base)_1-2 clusters compared to the (MSA)₂(base)_1-2 clusters. Hence, some of the steric hindrance and lack of hydrogen bond capacity previously observed in the (MSA)₂(base)_1-2 clusters is diminished in the corresponding (SA)₁(MSA)₁(base)_1-2 clusters. Cluster kinetics simulations reveal that the presence of an MSA molecule in the clusters enhances the cluster formation potential by up to a factor of 20. We find that the SA-MSA-DMA clusters have the highest cluster formation potential, and thus, this system should be further extended to larger sizes in future studies.

Gas-phase catalytic hydration of I2O5 in the polluted coastal regions: Reaction mechanisms and atmospheric implications

Marine aerosols play an important role in the global aerosol system. In polluted coastal regions, ultra-fine particles have been recognized to be related to iodine-containing species and is more serious due to the impact of atmospheric pollutants. Many previous studies have identified iodine pentoxide (I₂O₅, IP) to be the key species in new particles formation (NPF) in marine regions, but the role of IP in the polluted coastal atmosphere is far to be fully understood. Considering the high humidity and concentrations of pollutants in the polluted coastal regions, the gas-phase hydration of IP catalyzed by sulfuric acid (SA), nitric acid (NA), dimethylamine (DMA), and ammonia (A) have been investigated at DLPNO-CCSD(T)//ωB97X-D/aug-cc-pVTZ + aug-cc-pVTZ-PP with ECP28MDF (for iodine) level of theory. The results show that the hydration of IP involves a significant energy barrier of 22.33 kcal/mol, while the pollutants SA, NA, DMA, and A all could catalyze the hydration of IP. Especially, with SA and DMA as catalysts, the hydration reactions of IP present extremely low barriers and high rate constants. It is suggested that IP is unstable under the catalysis of SA and DMA to generate iodic acid, which is the key component in NPF in marine regions. Thus, the catalytic hydration of IP is very likely to trigger the formation of iodine-containing particles. Our research provides a clear picture of the catalytic hydration of IP as well as theoretical guidance for NPF in the polluted coastal atmosphere.

A theoretical study on the formation mechanism of carboxylic sulfuric anhydride and its potential role in new particle formation

New particle formation (NPF) is the major source of atmospheric aerosol particles. However, the chemical species involved and the exact mechanism are still unclear. Cycloaddition reaction of SO3 to carboxylic acids bas been identified as a possible formation mechanism of carboxylic sulfuric anhydrides which may be involved in NPF. Herein, energy profiles for forming diaterpenylic acetate sulfuric anhydride (DTASA) through cycloaddition of SO3 to diaterpenylic acid acetate (DTAA) and the potential role of DTASA in NPF were studied through computational methods combined with atmospheric cluster dynamics code (ACDC). Gas phase reaction barriers for the two carboxyl groups of DTAA are 0.4 and 0.6 kcal mol-1, respectively, illustrating a feasible formation mechanism for DTASA. According to thermodynamical analysis and dynamical simulations, atmospheric clusters containing DTASA and atmospheric nucleation precursors sulfuric acid (SA), ammonia (NH3) and dimethylamine (DMA) possess both thermodynamically and dynamically higher stabilities than those of DTAA-contained clusters. Furthermore, DTASA-NH3 and DTASA-DMA are more stable than SA-NH3 and SA-DMA, enabling DTASA, even carboxylic sulfuric anhydrides, to become potential participants in the atmospheric NPF process which may hence promote a better understanding of NPF.

Tri-Base Synergy in Sulfuric Acid-Base Clusters

Synergistic effects between different bases can greatly enhance atmospheric sulfuric acid (SA)-base cluster formation. However, only the synergy between two base components has previously been investigated. Here, we extend this concept to three bases by studying large atmospherically relevant (SA)3(base)3 clusters, with the bases ammonia (A), methylamine (MA), dimethylamine (DMA), trimethylamine (TMA) and ethylenediamine (EDA). Using density functional theory—ωB97X-D/6-31++G(d,p)—we calculate the cluster structures and vibrational frequencies. The thermochemical parameters are calculated at 29,815 K and 1 atm, using the quasi-harmonic approximation. The binding energies of the clusters are calculated using high level DLPNO-CCSD(T0)/aug-cc-pVTZ. We find that the cluster stability in general depends on the basicity of the constituent bases, with some noteworthy additional guidelines: DMA enhances the cluster stability, TMA decreases the cluster stability and there is high synergy between DMA and EDA. Based on our calculations, we find it highly likely that three, or potentially more, different bases, are involved in the growth pathways of sulfuric acid-base clusters.

Clusteromics II: Methanesulfonic Acid-Base Cluster Formation

The role of methanesulfonic acid (MSA) in atmospheric new particle formation remains highly uncertain. Using state-of-the-art computational methods, we study the electrically neutral (MSA)0-2(base)0-2 clusters, with base = ammonia (A), methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), and ethylenediamine (EDA). The cluster configurations are obtained using the ABCluster program and the number of initial cluster configurations is reduced based on PM7 calculations. Thermochemical parameters are calculated using the quasi-harmonic approximation based on the ωB97X-D/6-31++G(d,p) cluster structures and vibrational frequencies. The single point energies are calculated at the DLPNO-CCSD(T0)/aug-cc-pVTZ level of theory. We find that MSA shows a different interaction pattern with the bases compared to sulfuric acid and does not simply follow the basicity of the bases for these small clusters. In all cases, we find that the MSA-base clusters show very low cluster formation potential, indicating that electrically neutral clusters consisting solely of MSA as the clustering acid are most likely not capable of forming and growing under realistic atmospheric conditions.

Clusteromics I: Principles, Protocols, and Applications to Sulfuric Acid-Base Cluster Formation

We recently coined the term clusteromics as a holistic approach for obtaining insight into the chemical complexity of atmospheric molecular cluster formation and at the same time providing the foundation for thermochemical databases that can be utilized for developing machine learning models. Here, we present the first paper in the series that applies state-of-the-art computational methods to study multicomponent (SA)0-2(base)0-2 clusters, with SA = sulfuric acid and base = [ammonia (A), methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), and ethylenediamine (EDA)] with all combinations of the five bases. The initial cluster configurations are obtained using the ABCluster program and the number of relevant configurations are reduced based on PM7 and ωB97X-D/6-31++G(d,p) calculations. Thermochemical parameters are calculated based on the ωB97X-D/6-31++G(d,p) cluster structures and vibrational frequencies using the quasi-harmonic approximation. The single-point energies are refined with a high-level DLPNO-CCSD(T0)/aug-cc-pVTZ calculation. Using the calculated thermochemical data, we perform kinetics simulations to evaluate the potential of these small (SA)0-2(base)0-2 clusters to grow into larger cluster sizes. In all cases we find that having more than one type of base molecule present in the cluster will increase the potential for forming larger clusters primarily due to the increased available vapor concentration.

Toward a Holistic Understanding of the Formation and Growth of Atmospheric Molecular Clusters: A Quantum Machine Learning Perspective

The formation of atmospheric molecular clusters is an important stage in forming new particles in the atmosphere. Despite being a highly focused research area, the exact chemical species involved in the initial steps in new particle formation remain elusive. In this Perspective the main challenges and recent progression in the field are outlined with a special emphasis on the chemical complexity of the puzzle and prospect of modeling larger clusters. In general, there is a high demand for accurate and more complete quantum chemical data sets that can be applied in cluster distribution dynamics models and coupled to atmospheric chemical transport models. A view on how the community could reach this goal by applying data-driven machine learning approaches for more efficient exploration of cluster configurations is presented. A path toward larger clusters and direct molecular dynamics simulations of cluster formation and growth using machine learning models is discussed.