Atmospheric Cluster Dynamics Code Research Articles

Rapid iodine oxoacid nucleation enhanced by dimethylamine in broad marine regions

Abstract. Recent experiments have revealed a vital nucleation process of iodic acid (HIO3) and iodous acid (HIO2) under marine boundary layer conditions. However, HIO3–HIO2 nucleation may not effectively drive the observed rapid new particle formation (NPF) in certain coastal regions influenced by urban air masses. Dimethylamine (DMA) is a promising basic precursor to enhance nucleation considering its strong ability to stabilize acidic clusters and the wide distribution in marine atmosphere, while its role in HIO3–HIO2 nucleation remains unrevealed. Hence, a method combining quantum chemical calculations and Atmospheric Cluster Dynamics Code (ACDC) simulations was utilized to study the HIO3–HIO2–DMA nucleation process. We found that DMA can preferentially accept the proton from HIO3 as a basic precursor in the most stable configurations of HIO3–HIO2–DMA clusters. Kinetically, the participation of DMA in the cluster formation pathways of the iodine oxoacid system could be significant at the 10−1 to 1 pptv level of [DMA]. Furthermore, DMA can enhance the cluster formation rates of the HIO3–HIO2 system in marine and polar regions near DMA sources more than 103-fold. Compared to the classical nucleation mechanism, the HIO3–HIO2–DMA mechanism exhibits strong nucleation ability, worthy of consideration as a promising mechanism in marine and polar regions rich in amine sources. The newly proposed HIO3–HIO2–DMA ternary mechanism might provide an explanation for some missing fluxes of atmospheric iodine particles.

Reaction of SO3 with H2SO4 and its implications for aerosol particle formation in the gas phase and at the air–water interface

Abstract. The reactions between SO3 and atmospheric acids are indispensable in improving the formation of aerosol particles. However, relative to those of SO3 with organic acids, the reaction of SO3 with inorganic acids has not received much attention. Here, we explore the atmospheric reaction between SO3 and H2SO4, a typical inorganic acid, in the gas phase and at the air–water interface using quantum chemical (QC) calculations and Born–Oppenheimer molecular dynamics simulations. We also report the effect of H2S2O7, the product of the reaction between SO3 and H2SO4, on new particle formation (NPF) in various environments using the Atmospheric Cluster Dynamics Code (ACDC) kinetic model and QC calculations. The present findings show that the gas-phase reactions of SO3 + H2SO4 without and with water molecules are both low-energy-barrier processes. With the involvement of interfacial water molecules, H2O induced the formation of the S2O72-⋯H3O+ ion pair, HSO4- mediated the formation of the HSO4-⋯H3O+ ion pair, and the deprotonation of H2S2O7 was observed and proceeded on the picosecond timescale. The present findings suggest the potential contribution of the SO3–H2SO4 reaction to NPF and aerosol particle growth, showing that (i) although H2S2O7 is easily hydrolyzed with water to form H2SO4, it can directly participate in H2SO4–NH3-based cluster formation and can present a more obvious enhancement effect on SA–A-based cluster formation, and (ii) the formed interfacial S2O72- can attract candidate species from the gas phase to the water surface and, thus, accelerate particle growth.

Unexpected enhancement of sulfuric acid-driven new particle formation by alcoholic amines: The role of ion-induced nucleation

New particle formation (NPF) contributes more than half of the global aerosol. Diethanolamine (DEA) and methyldiethanolamine (MDEA) are the most common amines used to remove CO2 and H2S, which are lost to the atmosphere from CO2 chemical absorbers, livestock and consumer products and are involved in sulfuric acid (SA)-driven NPF. Ion-induced nucleation (IIN) is an important nucleation pathway for NPF. We investigated the role of IIN on DEA and MDEA enhancing SA-driven NPF using density functional method (DFT), molecular dynamics (MD) simulation and atmospheric cluster dynamics code (ACDC). The effects of SO42−, H3O+, NH4+, HSO4−, NO3−, ammonia, methylamine, dimethylamine, trimethylamine and water (W) on the nucleation of SA-DEA were further investigated. The enhancement ability of DEA is greater than that of dimethylamine (DMA) and MDEA. Participation in SA-based NPF is a removal pathway for DEA and MDEA. DEA-SA clusters are generated that not only aggregate DEA and SA molecules, but also increase further growth of atmospheric ions. The very low Gibbs formation free energy highlights the importance of ion-induced nucleation for SA-based NPF. The order of the ability of common atmospheric ions to increase the (SA)(DEA) cluster nucleation is SO42− > H3O+ > NH4+ > HSO4− > NO3−. The addition of 20 water molecules increases the (SA)(DEA)9 cluster from 1.882 nm to 2.053 nm, promoting SA-based NPF. The atmospheric ions accelerate the aggregation rate of the (SA)5(DEA)5 cluster within 15 ns?

Nitric Acid and Organic Acids Suppress the Role of Methanesulfonic Acid in Atmospheric New Particle Formation.

Multicomponent atmospheric molecular clusters, typically comprising a combination of acids and bases, play a pivotal role in our climate system and contribute to the perplexing uncertainties embedded in modern climate models. Our understanding of cluster formation is limited by the lack of studies on complex mixed-acid-mixed-base systems. Here, we investigate multicomponent clusters consisting of mixtures of several acid and base molecules: sulfuric acid (SA), methanesulfonic acid (MSA), nitric acid (NA), formic acid (FA), along with methylamine (MA), dimethylamine (DMA), and trimethylamine (TMA). We calculated the binding free energies of a comprehensive set of 252 mixed-acid-mixed-base clusters at the DLPNO-CCSD(T0)/aug-cc-pVTZ//ωB97X-D/6-31++G(d,p) level of theory. Combined with the existing datasets, we simulated the new particle formation (NPF) rates using the Atmospheric Cluster Dynamics Code (ACDC). We find that the presence of NA and FA had a substantial impact, increasing the NPF rate by 60% at realistic conditions. Intriguingly, we find that NA and FA suppress the role of MSA in NPF. These findings suggest that even high concentration of MSA has a limited impact on NPF in polluted regions with high FA and NA. We outline a method for generating a lookup table that could potentially be used in climate models that sufficiently incorporates all the required chemistry. By unraveling the molecular mechanisms of mixed-acid-mixed-base clusters, we get one step closer to comprehending their implications for our global climate system.

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.

The critical role of dimethylamine in the rapid formation of iodic acid particles in marine areas

Marine new particle formation (NPF) can affect cloud condensation nuclei (CCN) in the global atmosphere. Recently, iodic acid (IA) has been identified as a critical driver for marine NPF. However, atmospheric observations of IA cannot be associated with predicted particle formation rates. Given the complexity of atmospheric components, other species may promote IA particle formation. As an efficient stabilizer for acidic precursors, dimethylamine (DMA) has a wide distribution over the oceans. Hence, we investigated the nucleation process of DMA and IA under different atmospheric conditions and uncovered the corresponding nucleating mechanism using a quantum chemical approach and Atmospheric Cluster Dynamics Code (ACDC). The findings show that DMA can structurally stabilize IA via hydrogen and halogen bonds, and the clustering process is energy barrierless. Moreover, DMA can enhance the formation rate of IA clusters by five orders of magnitude, and its efficiency in promoting IA cluster formation is much higher than that of NH3. Compared to the nucleation via sequential addition of IA, the IA-DMA nucleation plays a more dominant role in nucleation kinetic. Thus, the effect of DMA on enhancing IA cluster stability and formation rate cannot be ignored, especially in the regions near the source of IA and DMA emissions. Broadly, the proposed IA-DMA nucleation mechanism may help to explain some missing sources of particles and, thus intensive marine NPF events.

Unexpectedly significant stabilizing mechanism of iodous acid on iodic acid nucleation under different atmospheric conditions

Iodous acid (HIO2) has been shown to play a stabilizing role in the nucleation of iodic acid (HIO3) (He et al., 2021). However, the stabilization effect and specific stabilizing mechanism of HIO2 on HIO3 nucleation under different atmospheric conditions remain unclear. Therefore, we studied these two issues under different temperatures and nucleation precursor concentrations using density functional theory combined with the Atmospheric Cluster Dynamics Code. We found that HIO2 can form clusters with HIO3 via strong hydrogen bonds, halogen bonds, and proton-transfer, substantially enhancing the stability of HIO3 clusters and decreasing the energy barrier of HIO3-based cluster formation at different temperatures and nucleation precursor concentrations. The particle formation rate and cluster concentrations of HIO3–HIO2 nucleation were negatively correlated with temperature and positively correlated with HIO2 concentration. The enhancements by HIO2 on the particle formation rate and cluster concentration of HIO3 nucleation were positively correlated with temperature and HIO2 concentration. Interestingly, even at a low HIO2 concentration (1.0 × 105 molecules cm−3), the enhancement on the particle formation rate and cluster concentration of HIO3 nucleation by HIO2 were both unexpectedly up to 4.1 × 104-fold at 283 K. Therefore, HIO3–HIO2 nucleation can be extremely rapid in cold regions, and the enhancement by HIO2 can be significant, especially in warm regions even at relatively high HIO2 concentrations.

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.

Atmospherically Relevant Chemistry and Aerosol box model – ARCA box (version 1.2)

Abstract. We introduce the Atmospherically Relevant Chemistry and Aerosol box model ARCA box (v.1.2.2). It is a zero-dimensional process model with a focus on atmospheric chemistry and submicron aerosol processes, including cluster formation. A novel feature in the model is its comprehensive graphical user interface, allowing for detailed configuration and documentation of the simulation settings, flexible model input, and output visualization. Additionally, the graphical interface contains tools for module customization and input data acquisition. These properties – customizability, ease of implementation and repeatability – make ARCA an invaluable tool for any atmospheric scientist who needs a view on the complex atmospheric aerosol processes. ARCA is based on previous models (MALTE-BOX, ADiC and ADCHEM), but the code has been fully rewritten and reviewed. The gas-phase chemistry module incorporates the Master Chemical Mechanism (MCMv3.3.1) and Peroxy Radical Autoxidation Mechanism (PRAM) but can use any compatible chemistry scheme. ARCA's aerosol module couples the ACDC (Atmospheric Cluster Dynamics Code) in its particle formation module, and the discrete particle size representation includes the fully stationary and fixed-grid moving average methods. ARCA calculates the gas-particle partitioning of low-volatility organic vapours for any number of compounds included in the chemistry, as well as the Brownian coagulation of the particles. The model has parametrizations for vapour and particle wall losses but accepts user-supplied time- and size-resolved input. ARCA is written in Fortran and Python (user interface and supplementary tools), can be installed on any of the three major operating systems and is licensed under GPLv3.

Effect of methyl hydrogen sulfate on the formation of sulfuric acid‐ammonia clusters: A theoretical study

AbstractMethyl hydrogen sulfate (MHS) as a common nucleation precursor that has important effect on new particle formation (NPF). Liu et al. showed that MHS and sulfuric acid (SA) generation are competitive due to consumption of the common precursor SO3, and the nucleation ability of SA is better than MHS. Thus, MHS inhibits the SA‐DMA‐based clusters formation particularly in regions with high [MO] (methanol) (Liu et al., Proc. Natl. Acad. Sci. U.S.A. 2019, 116, 24,966). However, in regions where [H2O] is much higher than [MO] ([SA] > > [MHS]), the SO3 consumed by the generation of less MHS will not significantly reduce the [SA], whether MHS still inhibits SA‐A‐based clusters formation and how MHS affects the growth pathways of MHS‐SA‐A‐based clusters remains unclear. Hence, quantum chemistry calculations combining Atmospheric Cluster Dynamics Code (ACDC) are used to investigate the role of MHS in the SA‐A‐based system. Our conclusions show two different effects of MHS in NPF process: “inhibiting” in regions with high [MO] and “weakly facilitating” in regions with high [H2O] and low [MO]. The growth pathways show that with the increasing [MHS], the role of MHS in NPF gradually changes from “transporter” to “participator”, and the contribution to the pathways increases from 7 to 85%. Our results contribute to understanding the NPF in low‐temperature regions with different concentrations of MO and H2O.

Molecular-level nucleation mechanism of iodic acid and methanesulfonic acid

Abstract. Both iodic acid (HIO3, IA) and methanesulfonic acid (CH3S(O)2OH, MSA) have been identified by field studies as important precursors of new particle formation (NPF) in marine areas. However, the mechanism of NPF in which IA and MSA are jointly involved is still unclear. Hence, we investigated the IA-MSA nucleation system under different atmospheric conditions and uncovered the corresponding nucleating mechanism at the molecular level for the first time, using a quantum chemical approach and Atmospheric Cluster Dynamics Code (ACDC). The findings show that the pure-IA nucleation rate was much lower than the results of CLOUD (Cosmics Leaving Outdoor Droplets) experiments. MSA can promote IA cluster formation through stabilizing IA via both hydrogen and halogen bonds, especially under conditions with lower temperatures, sparse IA, and rich MSA. However, the nucleation rate of the IA-MSA mechanism is much lower than that of field observations, indicating that the effect of additional nucleation precursors needs to be considered (e.g., H2SO4, HIO2, NH3, and amines). The IA-MSA nucleation mechanism revealed in this study may help to gain insight into the joint effect of marine sulfur- and iodine-containing components on marine NPF.

Pyruvic acid, an efficient catalyst in SO<sub>3</sub> hydrolysis and effective clustering agent in sulfuric-acid-based new particle formation

Abstract. The role of pyruvic acid (PA), one of the most abundant α-keto carboxylic acids in the atmosphere, was investigated both in the SO3 hydrolysis reaction to form sulfuric acid (SA) and in SA-based aerosol particle formation using quantum chemical calculations and a cluster dynamics model. We found that the PA-catalyzed SO3 hydrolysis is a thermodynamically driven transformation process, proceeding with a negative Gibbs free-energy barrier, ca. −1 kcal mol−1 at 298 K, ∼ 6.50 kcal mol−1 lower than that in the water-catalyzed SO3 hydrolysis. Results indicated that the PA-catalyzed reaction can potentially compete with the water-catalyzed SO3 reaction in SA production, especially in dry and polluted areas, where it is found to be ∼ 2 orders of magnitude more efficient that the water-catalyzed reaction. Given the effective stabilization of the PA-catalyzed SO3 hydrolysis product as SA⚫PA cluster, we proceeded to examine the PA clustering efficiency in a sulfuric-acid–pyruvic-acid–ammonia (SA-PA-NH3) system. Our thermodynamic data used in the Atmospheric Cluster Dynamics Code indicated that under relevant tropospheric temperatures and concentrations of SA (106 molec.cm-3), PA (1010 molec.cm-3) and NH3 (1011 and 5 × 1011 molec.cm-3), PA-enhanced particle formation involves clusters containing at most one PA molecule. Namely, under these monomer concentrations and 238 K, the (SA)2⚫PA⚫(NH3)2 cluster was found to contribute by ∼ 100 % to the net flux to aerosol particle formation. At higher temperatures (258 and 278 K), however, the net flux to the particle formation is dominated by pure SA-NH3 clusters, while PA would rather evaporate from the clusters at high temperatures and not contribute to the particle formation. The enhancing effect of PA was examined by evaluating the ratio of the ternary SA-PA-NH3 cluster formation rate to binary SA-NH3 cluster formation rate. Our results show that while the enhancement factor of PA to the particle formation rate is almost insensitive to investigated temperatures and concentrations, it can be as high as 4.7 × 102 at 238 K and [NH3] = 1.3 × 1011 molec.cm-3. This indicates that PA may actively participate in aerosol formation, only in cold regions of the troposphere and highly NH3-polluted environments. The inclusion of this mechanism in aerosol models may reduce uncertainties that prevail in modeling the aerosol impact on climate.

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.

Comparison results of eight oxygenated organic molecules: Unexpected contribution to new particle formation in the atmosphere

Recently, the correlation between the new particle formation (NPF) events and oxygenated organic molecules (OMs) was observed frequently in forest ambient. However, the understanding of OMs-driven NPF mechanism at the molecular level remains ambiguous. The participation of eight organic compounds (Orgs) together with sulfuric acid (SA) respectively in the initial steps of NPF was investigated by the quantum-chemical calculation and Atmospheric Cluster Dynamics Code (ACDC). Thermodynamic and structural analysis prove that most of (Org)x(SA)y (0 ≤ x ≤ 2; 0 ≤ y ≤ 2) clusters possess stable H-bonds, but other interactions, such as steric hindrance, should not be ignored when investigating their stabilities and reaction properties. Furthermore, the cluster formation rates of eight Org-SA systems are calculated and found to be different at three levels: (1) systems involved 3-carboxyheptanoic acid (CHA) and phthalic acid (PTA) present high formation rates exceeding 10−3 cm3 s−1, which indicate their high nucleation abilities; (2) systems containing cis-3-caric acid (CRA), limonic acid (LMA) and 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) have medium formation rate values from 10−6 to 10−4 cm3 s−1; and (3) systems including cis-pinic acid (PNA), 2-methyltetrols (MT) and 2-methylglyceric acid (MGA) present low formation rates less than 10−8 cm3 s−1. Our comparison results of theoretical researches about eight Orgs and SA indicate that OMs are expected to make important contributions to NPF under real atmospheric conditions. Especially, CHA and PTA, the crucial oxidation product of monoterpene and aromatic respectively, represent considerably strong potential abilities to form the critical clusters unexpectedly, and more attention should be paid to their effects on NPF in the real environment.

Influence of atmospheric conditions on the role of trifluoroacetic acid in atmospheric sulfuric acid–dimethylamine nucleation

Abstract. Ambient measurements combined with theoretical simulations have shown evidence that the tropospheric degradation end-products of Freon alternatives, trifluoroacetic acid (TFA), one of the most important and abundant atmospheric organic substances, can enhance the nucleation process based on sulfuric acid (SA) and dimethylamine (DMA) in urban environments. However, TFA is widespread all over the world under different atmospheric conditions, such as temperature and nucleation precursor concentration, which are the most important factors potentially influencing the atmospheric nucleation process and thus inducing different nucleation mechanisms. Herein, using the density functional theory combined with the Atmospheric Cluster Dynamics Code, the influence of temperature and nucleation precursor concentrations on the role of TFA in the SA–DMA nucleation has been investigated. The results indicate that the growth trends of clusters involving TFA can increase with the decrease in temperature. The enhancement on particle formation rate by TFA and the contributions of the SA–DMA–TFA cluster to the cluster formation pathways can be up to 227-fold and 95 %, respectively, at relatively low temperature, low SA concentration, high TFA concentration, and high DMA concentration, such as in winter, at the relatively high atmospheric boundary layer, or in megacities far away from industrial sources of sulfur-containing pollutants. These results provide the perspective of the realistic role of TFA in different atmospheric environments, revealing the potential influence of the tropospheric degradation of Freon alternatives under a wide range of atmospheric conditions.

Identification of molecular cluster evaporation rates, cluster formation enthalpies and entropies by Monte Carlo method

Abstract. We address the problem of identifying the evaporation rates for neutral molecular clusters from synthetic (computer-simulated) cluster concentrations. We applied Bayesian parameter estimation using a Markov chain Monte Carlo (MCMC) algorithm to determine cluster evaporation/fragmentation rates from synthetic cluster distributions generated by the Atmospheric Cluster Dynamics Code (ACDC) and based on gas kinetic collision rate coefficients and evaporation rates obtained using quantum chemical calculations and detailed balances. The studied system consisted of electrically neutral sulfuric acid and ammonia clusters with up to five of each type of molecules. We then treated the concentrations generated by ACDC as synthetic experimental data. With the assumption that the collision rates are known, we tested two approaches for estimating the evaporation rates from these data. First, we studied a scenario where time-dependent cluster distributions are measured at a single temperature before the system reaches a steady state. In the second scenario, only steady-state cluster distributions are measured but at several temperatures. Additionally, in the latter case, the evaporation rates were represented in terms of cluster formation enthalpies and entropies. This reparameterization reduced the number of unknown parameters, since several evaporation rates depend on the same cluster formation enthalpy and entropy values. We also estimated the evaporation rates using previously published synthetic steady-state cluster concentration data at one temperature and compared our two cases to this setting. Both the time-dependent and the two-temperature steady-state concentration data allowed us to estimate the evaporation rates with less variance than in the steady-state single-temperature case. We show that temperature-dependent steady-state data outperform single-temperature time-dependent data for parameter estimation, even if only two temperatures are used. We can thus conclude that for experimentally determining evaporation rates, cluster distribution measurements at several temperatures are recommended over time-dependent measurements at one temperature.

Impact of Quantum Chemistry Parameter Choices and Cluster Distribution Model Settings on Modeled Atmospheric Particle Formation Rates

We tested the influence of various parameters on the new particle formation rate predicted for the sulfuric - acid ammonia system using quantum chemistry and cluster distribution dynamics simulations, in our case ACDC (Atmospheric Cluster Dynamics Code). We found that consistent consideration of the rotational symmetry number of monomers (sulfuric acid and ammonia molecules, and bisulfate and ammonium ions) leads to a significant rise in the predicted particle formation rate, whereas inclusion of the rotational symmetry number of the clusters only changes the results slightly, and only in conditions where charged clusters dominate the particle formation rate. This is because most of the clusters stable enough to participate in new particle formation have a rotational symmetry number of one, and the few exceptions to this rule are positively charged. In contrast, the application of the quasi-harmonic correction for low-frequency vibrational modes tends to generally decrease predicted new particle formation rates, and also significantly alters the slope of the formation rate curve plotted against the sulfuric acid concentration which is a typical convention in atmospheric aerosol science. The impact of the maximum size of the clusters explicitly included in the simulations depends on the simulated conditions. The errors arising from a limited set of clusters are higher for higher evaporation rates, and thus tend to increase with temperature. Similarly, the errors tend to be higher for lower vapor concentrations. The boundary conditions for outgrowing clusters (which clusters are counted as formed particles) have only a small influence on the results, provided that the definition is chemically reasonable, and that the set of simulated clusters is sufficiently large. A comparison with data from the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber and a cluster distribution dynamics model using older quantum chemistry input data shows improved agreement when using our new input data, and the proposed combination of symmetry and quasi-harmonic corrections.

Nucleation mechanisms of iodic acid in clean and polluted coastal regions

In coastal regions, intense bursts of particles are frequently observed with high concentrations of iodine species, especially iodic acid (IA). However, the nucleation mechanisms of IA, especially in polluted environments with high concentrations of sulfuric acid (SA) and ammonia (A), remain to be fully established. By quantum chemical calculations and atmospheric cluster dynamics code (ACDC) simulations, the self-nucleation of IA in clean coastal regions and that influenced by SA and A in polluted coastal regions are investigated. The results indicate that IA can form stable clusters stabilized by halogen bonds and hydrogen bonds through sequential addition of IA, and the self-nucleation of IA can instantly produce large amounts of stable clusters when the concentration of IA is high during low tide, which is consistent with the observation that intense particle bursts were linked to high concentrations of IA in clean coastal regions. Besides, SA and A can stabilize IA clusters by the formation of more halogen bonds and hydrogen bonds as well as proton transfers, and the binary nucleation of IA-SA/A rather than the self-nucleation of IA appears to be the dominant pathways in polluted coastal regions, especially in winter. These new insights are helpful to understand the mechanisms of new particle formation induced by IA in clean and polluted coastal regions.

Atmospheric Sulfuric Acid‐Dimethylamine Nucleation Enhanced by Trifluoroacetic Acid

AbstractSulfuric acid (SA)‐dimethylamine (DMA)‐H2O cluster formation has been proven to be responsible for a significant part of new particle formation (NPF) in a Chinese megacity. However, the possible involvement of common atmospheric acids in the subsequent growth of SA‐DMA clusters remains elusive. We simulated formation and growth of clusters using atmospheric relevant concentrations of SA, DMA, and trifluoroacetic acid (TFA), a commonly observed atmospheric perfluorocarboxylic acid, using Density Functional Theory combined with Atmospheric Cluster Dynamics Code. The presence of TFA leads to complex cluster formation routes and an enhancement of NPF rates by up to 2.3 ([TFA] = 5.0 × 106 molecules cm−3, [SA] = 1.0 × 106 molecules cm−3, and [DMA] = 1.5 × 109 molecules cm−3). The agreement of (SA)1·(DMA)1‐2·(TFA)1 concentrations between simulations and ambient measurements during NPF events validates model predictions and implies that perfluorocarboxylic acids could potentially boost atmospheric SA‐DMA NPF rates.

Role of glycine on sulfuric acid-ammonia clusters formation: Transporter or participator

Glycine (Gly) is ubiquitous in the atmosphere and plays a vital role in new particle formation (NPF). However, the potential mechanism of its on sulfuric acid (SA) - ammonia (A) clusters formation under various atmospheric conditions is still ambiguous. Herein, a (Gly)x·(SA)y·(A)z (z ≤ x + y ≤ 3) multicomponent system was investigated by using density functional theory (DFT) combined with Atmospheric Cluster Dynamics Code (ACDC) at different temperatures and precursor concentrations. The results show that Gly, with one carboxyl (–COOH) and one amine (–NH2) group, can interact strongly with SA and A in two directions through hydrogen bonds or proton transfer. Within the relevant range of atmospheric concentrations, Gly can enhance the formation rate of SA-A-based clusters, especially at low temperature, low [SA], and median [A]. The enhancement (R) of Gly on NPF can be up to 340 at T = 218.15 K, [SA] = 104, [A] = 109, and [Gly] = 107 molecules/cm3. In addition, the main growth paths of clusters show that Gly molecules participate into cluster formation in the initial stage and eventually leave the cluster by evaporation in subsequent cluster growth at low [Gly], it acts as an important “transporter” to connect the smaller and larger cluster. With the increase of [Gly], it acts as a “participator” directly participating in NPF.