Interactions of sulfuric acid with common atmospheric bases and organic acids: Thermodynamics and implications to new particle formation

Interaction between hydroxymethanesulfonic acid and several organic compounds and its atmospheric significance

The interactions of the micro-mechanism of hydroxymethanesulfonic acid (HMSA) with the typical small organic molecule in atmospheric (X = methanol, formaldehyde, formic acid, methyl formate, dimethyl ether, acetone) has been investigated by density functional theory (DFT), quantum theory of atoms in molecules (QTAIM), Generalized Kohn-Sham Enery Decomposition Analysis (GKS-EDA) and the atmospheric clusters dynamic code (ACDC). The results of DFT show that the stable six- to eight-membered ring structures are easily formed in HMSA-X clusters. According to the topological analysis results of the AIM theory and the IRI method, a strong hydrogen bonding interaction is present in the complex. GKS-EDA results show that electrostatic energy is the main contributor to the interaction energy as it accounts for 51 %-55 % of the total attraction energy. The evaporation rates of HMSA-HMSA and HMSA-HCOOH clusters were much lower than those of the other HMSA complexes. In addition, the Gibbs energy of formation (ΔG) of HMSA-X dimers is investigated under atmosphere temperature T = 217-298 K and p = 0.19-1.0 atm, the ΔG decreased with decreasing of the atmosphere temperature and increased with the decrease of atmospheric pressure, indicating that the low temperature and high pressure may significantly facilitate to the formation of dimers.

Structural Diversity of Protonated Citric Acid-Ammonia Clusters and Its Atmospheric Implication

Various acid-base molecular clusters involving organic species can serve as precursors that play important roles in the formation of an atmospheric aerosol. Due to its structural flexibility and its ability to form multiple hydrogen bonds, citric acid acts as a key species in forming clusters that are critical in the nucleation of related aerosol precursors. Thus, it is provoking to characterize the structures of these clusters at the molecular level. In this paper, protonated citric acid-ammonia clusters of various sizes were generated by electrospray ionization and studied by tandem mass spectrometry. The structures of [(CA)2+NH4]1+ and [(CA)4+NH4]1+ were further characterized by the method of infrared photodissociation (IRPD) spectroscopy. Combined with theoretical calculations, it is found that the most stable structures of the dimeric and tetrameric isomers show the shapes of an ingot and a lantern, respectively. It has been revealed that the temperature has a great effect on the contributions of different isomers for both dimers and tetramers. The dominat isomers are found to have more open structures at higher temperatures, facilitating the growth of clusters through new hydrogen bonds.

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.

Hydrogen-Bonding Interactions of Malic Acid with Common Atmospheric Bases

Malic acid (MA) (C₄H₆O₅) is one of the most important organic constituents of fruits that is widely used in food and beverage industries. It is also detected in the atmospheric aerosol samples collected in different parts of the world. Considering the fact that secondary organic aerosols have adverse impacts on the global atmosphere and climate and a molecular-level understanding of the compositions and formation mechanism of secondary organic aerosols is necessary, we have performed systematic density functional electronic structure calculations to investigate the hydrogen-bonding interactions between MA and several naturally occurring nitrogen-containing atmospheric bases such as ammonia and amines that are derived from ammonia by the substitution of hydrogens by a methyl group. The base molecules were allowed to interact with the carboxylic COOH and the hydroxyl-OH group of the MA separately. While at both sites, MA produces energetically stable binary complexes with bases with large negative values of binding energy, the thermodynamical stability, at an ambient temperature and pressure of 298.15 K and 1 atm, respectively, is favored only for the clusters formed at the COOH site. A much larger red shift of the carboxylic-OH stretch than that of the hydroxyl-OH reinforces the preference of this site for cluster formation. Both the binding electronic energy and binding free energy of MA-ammonia complexes are lower than those of MA-amine complexes, although the amines are derivatives of NH₃. The large increase in the Rayleigh activities upon cluster formation indicates that the MA-atmospheric base cluster may interact strongly with solar radiation. The detailed analysis of the structural, energetic, electrical, and spectroscopic properties of the binary complexes formed by MA with atmospheric bases shows that MA could participate in the atmospheric nucleation processes and subsequently contribute effectively to new particle formation in the atmosphere.

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.

The driving effects of common atmospheric molecules for formation of prenucleation clusters: the case of sulfuric acid, formic acid, nitric acid, ammonia, and dimethyl amine

How secondary aerosols form is critical as aerosols' impact on Earth's climate is one of the main sources of uncertainty for understanding global warming. The beginning stages for formation of prenucleation complexes, that lead to larger aerosols, are difficult to decipher experimentally. We present a computational chemistry study of the interactions between three different acid molecules and two different bases. By combining a comprehensive search routine covering many thousands of configurations at the semiempirical level with high level quantum chemical calculations of approximately 1000 clusters for every possible combination of clusters containing a sulfuric acid molecule, a formic acid molecule, a nitric acid molecule, an ammonia molecule, a dimethylamine molecule, and 0-5 water molecules, we have completed an exhaustive search of the DLPNO-CCSD(T)/CBS//ωB97X-D/6-31++G** Gibbs free energy surface for this system. We find that the detailed geometries of each minimum free energy cluster are often more important than traditional acid or base strength. Addition of a water molecule to a dry cluster can enhance stabilization, and we find that the (SA)(NA)(A)(DMA)(W) cluster has special stability. Equilibrium calculations of SA, FA, NA, A, DMA, and water using our quantum chemical ΔG° values for cluster formation and realistic estimates of the concentrations of these monomers in the atmosphere reveals that nitric acid can drive early stages of particle formation just as efficiently as sulfuric acid. Our results lead us to believe that particle formation in the atmosphere results from the combination of many different molecules that are able to form highly stable complexes with acid molecules such as SA, NA, and FA.

Hydrogen-Bond Topology Is More Important Than Acid/Base Strength in Atmospheric Prenucleation Clusters

We explored the hypothesis that on the nanoscale level, acids and bases might exhibit different behavior than in bulk solution. Our study system consisted of sulfuric acid, formic acid, ammonia, and water. We calculated highly accurate Domain-based Local pair-Natural Orbital- Coupled-Cluster/Complete Basis Set (DLPNO-CCSD(T)/CBS) energies on DFT geometries and used the resulting Gibbs free energies for cluster formation to compute the overall equilibrium constants for every possible cluster. The equilibrium constants combined with the initial monomer concentrations were used to predict the formation of clusters at the top and the bottom of the troposphere. Our results show that formic acid is as effective as ammonia at forming clusters with sulfuric acid and water. The structure of formic acid is uniquely suited to form hydrogen bonds with sulfuric acid. Additionally, it can partner with water to form bridges from one side of sulfuric acid to the other, hence demonstrating that hydrogen bonding topology is more important than acid/base strength in these atmospheric prenucleation clusters.

Synergistic effect of glutaric acid and ammonia/amine/amide on their hydrates in the clustering: A theoretical study

The formation of molecular clusters makes influence on the atmosphere. The clusters of glutaric acid (GA) and common ammonia (A), amine (methylamine MA, dimethylamine DMA) and representative amide (urea U) along with water molecule were systematically studied theoretically. GA-A-nW (n = 1, 2), GA-MA-nW (n = 1, 2), GA-DMA-1W and GA-U-nW (n = 1-6) are predicted to be feasible thermodynamically with the hydrogen bonds as interaction force. GA and urea promote the clustering synergistically, and ammonia, methylamine, dimethylamine promote the clustering of small GA hydrates (n = 1-2), while inhibit that of large GA hydrates (n = 3-6). The results of humidity show that un-hydrate or mono-hydrate is the main form of GA-mbase-nW (m = 0, 1; n = 1-6) under relative humidity of 20%, 50% and 80%. The global minima remain dominant over the temperature range of 220-320 K. GA contributes more to the Rayleigh scattering properties than sulfuric acid. More importantly, the local minima can undergo isomerization to form the global minima crossing a free energy barrier ranging from 6.66 to 11.78 kcal mol^-1. This study indicates that GA and base molecules play a synergistic role to promote the formation of clusters. We hope it can provide more insights on interesting clustering in theory.

Application of an aerosol electrical mobility spectrum analyzer: Charged-particle polarity ratio measurement in the Antarctic and Arctic regions

An aerosol electrical mobility spectrum analyzer (AEMSA), developed at Hanyang University, was employed to investigate the particle charge characteristics in the Antarctic and Arctic regions. The particle charge characteristics in these areas were compared with the charging state in Ansan, South Korea, located in the midlatitude, where artificial factors, such as human activity, urbanization, and traffic, might result in a higher total concentration. Furthermore, in Ansan, South Korea, the charged-particle polarity ratio was very stable and was close to 1. However, notably different particle charge characteristics were obtained in the Antarctic and Arctic regions. The imbalance between the numbers of positively and negatively charged particles was evident, resulting in more positive charges on the atmospheric particles. On average, the positively charged particle concentrations in the Antarctic and Arctic areas were 1.4 and 2.8 times higher, respectively, compared with the negatively charged particles. The developed AEMSA system and the findings of this study provide useful information on the characteristics of atmospheric aerosols in the Antarctic and Arctic regions and can be further utilized to study particle formation mechanisms.