Understanding Hygroscopic Nucleation of Sulfate Aerosols

Letter Cite This: J. Phys. Chem. Lett. 2019, 10, 1126−1132

pubs.acs.org/JPCL

Understanding Hygroscopic Nucleation of Sulfate Aerosols: Combination of Molecular Dynamics Simulation with Classical Nucleation Theory Zheng Zhao,† Kewei Kong,† Shixian Wang,† Yingcheng Zhou,† Daojian Cheng,*,† Wenchuan Wang,† Xiao Cheng Zeng,*,†,‡ and Hui Li*,† †

J. Phys. Chem. Lett. Downloaded from pubs.acs.org by WEBSTER UNIV on 02/27/19. For personal use only.

Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China ‡ Department of Chemistry, University of NebraskaLincoln, Lincoln, Nebraska 68588, United States S Supporting Information *

ABSTRACT: We present a combined molecular dynamics (MD) and classical nucleation theory (CNT) approach to address many issues regarding the nucleation of inorganic aerosols. By taking parameters from MD simulations, we find the CNT predicts fairly reasonable free-energy profiles for the hygroscopic nucleation of aerosols. Moreover, we find that the ionization of sulfates can play a key role in stabilizing aqueous clusters and that both the size of the critical nucleus and the nucleation barrier can be significantly lowered by the H2SO4 and NH4HSO4, whereas the effect of NH3 on nucleation is negligible. NH4HSO4 provides stronger enhancement effect to aerosol formation than H2SO4. In view of the consistency between the theoretical prediction and experimental observation, the combination of MD simulation and CNT appears to be a valuable approach to gain deeper understanding of how aerosol nucleation is affected by different chemical species.

A

should play a key role in the formation of cloud/fog/mist/haze droplets. Previous investigations suggested that although the sulfuric acid plays a major role in atmospheric nucleation, the binary nucleation of sulfuric acid and water alone cannot account for the high new-particle formation rate in the polluted atmosphere.10 On the other hand, it is found that some base molecules, such as ammonia and amines, can increase the stability and decrease the evaporation of embryonic clusters, thereby enhancing the aerosol nucleation.11−14 Previous cloud chamber study and field observation in the atmosphere have shown that the ammonia sulfate is a major source of aerosols because a large amount of (NH3)m·(H2SO4)n clusters can be observed during the hygroscopic nucleation of aerosols.2,11 Despite these previous observations, the exact contribution of the chemical compositions to the nucleation rate is still incompletely understood.2,15 High-level quantum mechanical calculations have been widely used to study the physical chemistry of the aerosol clusters involving various pollution chemicals. For example, the evaporation/condensation rate and other dynamic properties of clusters containing H2SO4, NH3, and NH4HSO4 were accurately evaluated based on the calculated binding energies.16−21 Because of the limitation of computer speed,

tmospheric aerosols have profound impacts on many aspects of life on earth, including weather, climate, air quality, and human health.1−3 The hygroscopic nature of aerosols is a key concept in the field of cloud chemistry and physics.4,5 In a typical open-air environment, the nucleation of a pure water droplet can hardly occur due in part to the requirement of a high supersaturation of water vapor and the lack of clean air. Rather, through absorbing and evaporating water, aerosols can act as the cloud condensation nuclei (CCN) and induce the formation of cloud/fog/mist/haze droplets, thereby affecting the radiation balance in the atmosphere and/or the regional climate.6 Hence, understanding the hygroscopic nucleation of aerosol is one of the central topics in atmospheric science.7,8 The classical nucleation theory (CNT) is a thermodynamic theory widely used to describe the thermodynamics of nucleus formation from metastable phase, which certainly can be applied to study hygroscopic nucleation of aerosol. Specifically, the formation free energy of an aerosol cluster, ΔG, increases with its size at the initial stage of nucleation until it reaches the “critical nucleus” with the maximum ΔG*. The latter is also viewed as the nucleation barrier. Beyond the critical nucleus, the aerosol growth becomes kinetically favorable.9 If the aerosol is pure water, even at high supersaturation, the critical nucleus is still around hundreds of nanometers, thereby having very high nucleation barrier. In a realistic atmosphere, it is expected that the hydrophilicity of chemicals in the aerosol © XXXX American Chemical Society

Received: January 17, 2019 Accepted: February 25, 2019 Published: February 25, 2019 1126

DOI: 10.1021/acs.jpclett.9b00152 J. Phys. Chem. Lett. 2019, 10, 1126−1132

Letter

The Journal of Physical Chemistry Letters most ab initio studies focused on small aerosol clusters. To date, few studies have reported on the physicochemical properties of the aerosol in the radius range of 0.5−2.5 nm, which covers the range of suggested radius (0.65−0.95 nm) for the critical nucleus in atmospheric or experimental conditions.1,9 Note also that the conventional free-energy computation methods such as umbrella sampling or free-energy perturbation are unrealistic for exploring the huge phase space of such large systems, even by using classic molecular dynamics (MD) simulation. Hence, to quantitatively assess how different chemical compositions can enhance the rate of aerosol formation, a more cost-effective and yet quantitative method is needed to evaluate the free energy of the critical nucleus, as well as the growth process of aerosol from molecular cluster of ∼1 nm to the cloud droplet of ∼1 mm. Because CNT is commonly used to describe the thermodynamics of new particle formation and its validity at nanoscale has been confirmed by atomistic simulation,22,23 herein, we present a combined MD/CNT approach to study aerosol nucleation and growth. To this end, the structural properties of different sized sulfate/water aerosols are investigated by using both first principles and classical MD simulations. Structural and Dynamical Properties. Born−Oppenheimer molecular dynamics (BOMD) simulations are performed for model aerosol clusters with radii from ∼0.5 nm (30 water molecules) to ∼1.3 nm (300 water molecules) to investigate the hygroscopic nucleation process of aerosols containing different numbers of H2SO4, NH3, and NH4HSO4 molecules. With the same sulfate cores in BOMD simulations, the radius of aerosol clusters in classical molecular dynamics (CMD) simulations is extended to be ∼2.5 nm (2000 water molecules). The details of BOMD and CMD simulations are given in the Supporting Information. Spherical shapes are reserved for all the clusters during the BOMD and classical MD simulations; for example, snapshots of sulfate-(H2O)200 clusters with different chemical species are shown in Figure 1. The radial distribution of number density ρ(r) displays that the densities at interior regions of aerosol clusters are close to the bulk density of liquid water (∼33.46 nm−3) at room temperature (Figure S1a−f).24 The effective radii of the aerosol particles are then estimated based on the density distributions, as listed in Tables S1−S2. Because structural features of aerosols such as local atomic structures, density distributions, and radial distribution functions (RDFs) are nearly independent of the size of clusters, here we only take the trajectories of (H2O)200 clusters from BOMD simulations as the example to demonstrate the microstructures of the clusters with different chemical species. The ionization processes of H2SO4 and NH4HSO4 can be described by time evolution of the distance Rion−com between ion or molecule and the center of mass (COM) of the aerosol cluster, as displayed in panels b and c of Figure 2, respectively. Both H2SO4 and NH4HSO4 are ionized and turn into SO42−, NH4+, and H+, but the weak electrolyte NH3 keeps its molecular form during the MD simulation, as shown in Figure 2a. It is also observed that the dissociated proton sometime attaches to SO42−, leading to a dynamic equilibrium between SO42− and HSO4−. The trajectories also show that the ionized SO42− keeps staying at the center of the cluster, while both NH3 and NH4+ exhibit weak surface preference, as shown by the radial distribution of ion densities (Figure 2f−j), consistent with previous spectroscopic observation.25 To gain deeper

Figure 1. Snapshots of the equilibrium structures of aerosol cluster models in BOMD simulations: (a) (H2O)200; (b) NH3@(H2O)200; (c) H 2 SO 4 @(H 2 O) 2 0 0 ; (d) NH 4 HSO 4 @(H 2 O) 2 0 0 ; (e) (f) (H2SO4)2(NH4HSO4)2@(H2O)200; (H2SO4)4(NH4HSO4)4@(H2O)200. Color code: red, O; white, H ; yellow, S; blue, N.

insight into the cluster structures, the radial and angular distribution functions are also calculated (Figures S2 and S3), suggesting the hydrogen bond formation between ion and water. On the basis of this information, the angular effect on interactive energy u(rij) is also considered in surface tension evaluation. The ionization also has significant impact on dynamic properties of aerosol clusters, as listed in Tables S1 and S2. Vapor Pressure, Surface Tension, and Solvation Energy. According to the CNT (eq S2, Supporting Information), the free-energy change, ΔG, for the formation of an aerosol cluster is dependent on the vapor pressure, Pr, and the surface tension, σ, which can be computed from MD simulations. All the structural and energetic data of clusters with various sizes and chemical compositions are summarized in Tables S1 and S2. As shown in Figure S4a−f, the calculated pressure tensor PN(R) exhibits a maximum at the surface region of each cluster due to the high surface tension. The value of Pr is computed from the curve of PN(R) at the position of effective radius Re (Figure S4), which also decreases with increasing the cluster size, as shown in Figure 3a. The Pr values computed from BOMD simulations are slightly larger than those from the CMD simulations, but the trends are the same. Furthermore, the introduction of H2SO4, NH3, or NH4HSO4 always leads to lower Pr than that of the pure water cluster, implying the electrolyte solutes lower the driving force to water evaporation. 1127


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Figure 2. Distance Rion−com between ion and the center of mass (COM) for aerosol clusters versus the time: (a) NH3@(H2O)200; (b) H2SO4@(H2O)200; (c) NH4HSO4@(H2O)200; (d) (H2SO4)2(NH4HSO4)2@(H2O)200; (e) (H2SO4)4(NH4HSO4)4@(H2O)200. Density profiles of water and other individual components in clusters: (f) NH3@(H2O)200; (g) H2SO4@(H2O)200; (h) NH4HSO4@ (H2O)200; (i) (H2SO4)2(NH4HSO4)2@(H2O)200; (j) (H2SO4)4(NH4HSO4)4 @(H2O)200 at 300 K. In panels d and e, only one H2SO4 and one NH4HSO4 are tracked. The trajectories are taken from BOMD simulations.

observed in previous experiments.29−31 Both Pr and σ calculated in this work are consistent with previous calculation results for water droplets (Figure S5a,b).24,28 The hygroscopic nucleation of aerosol to cloud droplet may surpass 5 orders of magnitude of cluster size; thus, for large clusters beyond the limitation of atomistic simulation, the values of Pr and σ can be extrapolated using parameters from the least-squares fitting with the Kelvin26 and Tolman equations,32 as shown in Figure S6a,b. The third-term contribution to the ΔG of hygroscopic nucleation of aerosol is the interaction free energy between electrolytes and solvent, i.e., the solvation free energy, ΔGsol.

The ability to lower Pr is in the order of NH4HSO4 > H2SO4 > NH3, consistent with the order of diffusion coefficients. Both BOMD and CMD simulations give close values of surface tension, σ, which increase with the cluster size, as shown in Figure 3b. The opposite cluster size dependence for σ and Pr is known as the Kelvin or Tolman effect.26,27 The computed values of σ are also consistent with the known trend that a small amount of dissolved salts usually enhances the surface tension.28 Figure 3b demonstrates that the ionized H2SO4/NH4HSO4 can apparently increase the value of σ by increasing the cohesive energy of surface water, while the effect of NH3 on surface tension is negligible. This trend was also 1128


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As demonstrated by the solid and open dots in Figure 4a, the BOMD and CMD simulations give highly consistent values of ΔG. Hence, the ΔG profiles versus particle size are fitted to the Kelvin equation for the data taken from CMD simulations.3,9 For cluster sizes smaller than the critical radius rc, the ΔG is dominated by creating a new surface area. When the particle size is greater than rc, the condensation term becomes more important, leading to decreased ΔG. The relative humidity RH dominates both rc and ΔG* of the clusters. For example, rc (21.8 nm) and ΔG* (676.2 eV) of pure water at RH = 1.05 (Figure 4b) are 8.48 and 61.7 times larger than those (rc = ∼2.57 nm, and ΔG* = ∼10.95 eV) at RH = 1.5 (Figure 4a), indicating the homogeneous nucleation of pure water requires extremely high RH. Note that for pure water clusters at RH = 1.5, the ΔG profile calculated with experimentally measured Pr and σ of bulk water40 (black solid line in Figure 4a) shows slightly larger critical nucleus (rc = ∼2.6 nm) and higher nucleation barrier (ΔG* = ∼12.24 eV) compared to the ΔG profile from MD simulations (red lines in Figure 4a), because of larger Pr and smaller σ for highly curved surface of small-sized cluster (Figure 3). In other words, the CNT tends to overestimate the nucleation barrier if Pr and σ are measured based on bulk water. The solvation free energy, ΔGsol, leads to the negative value of ΔG in region of small size (R < 1 nm), implying that the sulfate aerosol with a small number of water molecules is kinetically stable. This result is consistent with the observation of the spontaneous nucleation of small aerosol clusters with H2SO4 and NH4HSO4 in previous experiments.15,41,42 Figure 4 demonstrates that the electrolyte solute can greatly reduce rc and ΔG* of aerosols. As listed in Table 1, the reduction of ΔG* by a single solute molecule follows the order ΔΔG* (NH4HSO4) (5.74 eV) > ΔΔG* (H2SO4) (3.30 eV) > ΔΔG* (NH3) (0.73 eV) at RH = 1.5, suggesting that the ionization of H2SO4 and NH4HSO4 can lead to higher stability for critically sized aerosol than the weak electrolyte NH3. The reduction of rc follows the same order. Although rc and ΔG* are much larger at lower relative humidity (RH = 1.05), the reduction of both values caused by solute molecules shows a similar trend (Figure 4b). In particular, the rc and ΔG* of the aerosol cluster with (H2SO4)4·(NH4HSO4)4 is around 1/4 and 1/20 of those of pure water cluster, respectively. Note that ΔΔG*(NH4HSO4) is much larger than the sum of ΔΔG* (H2SO4) and ΔΔG*(NH3), consistent with the fact that salification of H2SO4 and NH3 can greatly enhance the formation of aerosols.4,38 Moreover, rc and ΔG* are further reduced as the number of solute molecules increases. ΔG* of (H2SO4)2·(NH4HSO4)2 is only ∼0.07 eV, and the largest cluster in the present work, (H2SO4)4·(NH4HSO4)4, shows a barrierless ΔG profile (the green line in Figure 4a) for the hygroscopic nucleation at RH = 1.5. Both clusters were found in the cloud chamber and field measurements.2,15 It is further found that the nucleation can happen even for aerosols with large sulfate cores at RH < 1 if the vapor pressure of the cluster is significantly lowered by the solutes. Here, nucleation in (H2SO4)2(NH4HSO4)2@(H2O)n and (H2SO4)4(NH4HSO4)4@(H2O)n at RH = 0.9 requires large critical nucleus and has extremely high nucleation barrier (Figure 4c), while no nucleation happens for the remaining clusters at the same RH. At RH = 0.8, no nucleation can happen for all the model aerosols (Figure 4d). The nucleation rates, J, of aerosols containing different solutes are compared based on the Arrhenius equation (eq S6),

Figure 3. (a) Comparing the pressure Pr for pure water and ionhydrate clusters from BOMD (open symbols) and CMD simulations (solid symbols); (b) comparison of the surface tension σ of pure water and that of ion-hydrate clusters from BOMD and CMD simulations.

As H2SO4 and NH4HSO4 are fully ionized in clusters, ΔGsol can be divided into two parts: (1) the free energy of molecular dissociation ΔGdiss and (2) the absolute ΔGsol of ionized groups SO42−, H+, or NH4+. ΔGdiss is taken from MP2/augCCPVDZ calculation with Gaussian09 package,33 and the absolute ΔGsol data are from literature.34−37 The ion groups adopt well-formed hydrated structures in the aerosol because large numbers of water molecules are involved. It is assumed that the total ΔGsol for a cluster is a simple summation of ΔGdiss and ΔGsol of all the solute molecules and independent of the cluster size, as listed in Tables S3 and S4. The solvation free energy is in the order ΔGsol(NH4HSO4) (−2.36 eV) < ΔGsol(H2SO4) (−1.50 eV) < ΔGsol(NH3) (−0.34 eV), consistent with the order of enhancement effect to aerosol nucleation by the three electrolytes. Free Energy of Hygroscopic Nucleation. The ΔG profiles at various levels of relative humidity (RH = 1.5, 1.05, 0.9, and 0.8) are calculated. The high RH (1.5) and low RH (1.05, 0.9, and 0.8) correspond to the extreme humid condition in the experiment of condensation particle counter8,38 and the normal condition in the warm cloud in the troposphere,39 respectively. 1129


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Figure 4. Computed free-energy change for pure water and sulfate/water clusters at relative humidity of (a) RH = 1.5, (b) RH = 1.05, (c) RH = 0.9, and (d) RH = 0.8. The solid spheres and open squares in panel a represent the data from BOMD and CMD simulations, respectively. The solid spheres in panel b represent the data from BOMD. R denotes the radius of the cluster.

Table 1. Calculated Critical Radius, rc (nm), Nucleation Barrier, ΔG* (eV), and Reduction of the Nucleation Barrier Compared with Pure Water, ΔΔG* (eV), at RH = 1.5 and 1.05, as well as Nucleation Rate, J (J/J0), at RH = 1.5 RH = 1.5 system

rc

ΔG*

ΔΔG*

H2O NH3 H2SO4 NH4HSO4 2H2SO4· 2NH4HSO4 4H2SO4· 4NH4HSO4

2.57 2.42 2.26 2.01 1.80 1.66

10.95 10.22 7.65 5.21 0.07 0

0 0.73 3.30 5.74 10.88 10.95

RH = 1.05 J/J0 4.76 9.24 1.69 1.99 0.0663 1

× × × ×

10−185 10−173 10−129 10−88

rc

ΔG*

ΔΔG*

21.8 19.1 15.5 7.12 5.58 4.95

676.2 453.6 219.3 94.92 52.77 30.72

0 222.6 456.9 581.3 623.4 645.5

cluster (H2SO4)4·(NH4HSO4)4 can already yield a barrierless free-energy surface for hygroscopic nucleation at high RH. Overall, the combination of MD simulation and CNT appears to be a valuable approach for addressing many issues regarding the nucleation of inorganic aerosols in both qualitative and quantitative fashions, particularly the relation between the size of critical nucleus and the number of sulfate molecules, the role of ammonia in nucleation, the enhancement effect to the nucleation rate due to different chemical species, and the ionization effect. This new theoretical−computation approach can be also used in the future to quantify the chemical makeup of new particle formation in the atmosphere.

which is sensitive to the nucleation barrier (Figure S7). As listed in Table 1, the value of J (RH = 1.5) can differ by hundreds of orders of magnitude between pure water clusters and sulfate aerosol, indicating that the strong electrolyte is necessary for homogeneous nucleation of hygroscopic aerosol even at high RH. In summary, by taking values of the vapor pressure and surface tension from MD simulations, as well as the calculated solvation free energy, the CNT predicts fairly reasonable freeenergy profiles for the hygroscopic nucleation of aerosols at a given relative humidity. The ionization of H2SO4 and NH4HSO4 plays a key role in lowering the nucleation barrier and the size of critical nucleus, thereby greatly promoting the formation of the hydrous aerosols. Moreover, NH4HSO4 exhibits the highest affinity to water and leads to higher stability for the aerosol cluster than sulfuric acid. It is also found that increasing the number of H2SO4 and NH4HSO4 can further lower the nucleation barrier, and the largest sulfate

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpclett.9b00152. 1130


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Mogo, S.; Nieminen, T.; Onnela, A.; Pereira, P.; Petäjä, T.; Schnitzhofer, R.; Seinfeld, J. H.; Sipilä, M.; Stozhkov, Y.; Stratmann, F.; Tomé, A.; Vanhanen, J.; Viisanen, Y.; Vrtala, A.; Wagner, P. E.; Walther, H.; Weingartner, E.; Wex, H.; Winkler, P. M.; Carslaw, K. S.; Worsnop, D. R.; Baltensperger, U.; Kulmala, M. Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation. Nature 2011, 476, 429. (12) Kurtén, T.; Loukonen, V.; Vehkamäki, H.; Kulmala, M. Amines are likely to enhance neutral and ion-induced sulfuric acid-water nucleation in the atmosphere more effectively than ammonia. Atmos. Chem. Phys. 2008, 8 (14), 4095−4103. (13) Smith, J. N.; Barsanti, K. C.; Friedli, H. R.; et al. Observations of aminium salts in atmospheric nanoparticles and possible climatic implications. Proc. Natl. Acad. Sci. U. S. A. 2010, 107 (15), 6634− 6639. (14) Yao, L.; Garmash, O.; Bianchi, F.; Zheng, J.; Yan, C.; Kontkanen, J.; Junninen, H.; Mazon, S. B.; Ehn, M.; Paasonen, P.; Sipilä, M.; Wang, M.; Wang, X.; Xiao, S.; Chen, H.; Lu, Y.; Zhang, B.; Wang, D.; Fu, Q.; Geng, F.; Li, L.; Wang, H.; Qiao, L.; Yang, X.; Chen, J.; Kerminen, V.-M.; Petäjä, T.; Worsnop, D. R.; Kulmala, M.; Wang, L. Atmospheric new particle formation from sulfuric acid and amines in a Chinese megacity. Science 2018, 361 (6399), 278−281. (15) Almeida, J.; Schobesberger, S.; Kürten, A.; Ortega, I. K.; Kupiainenmäaẗ tä, O.; Praplan, A. P.; Adamov, A.; Amorim, A.; Bianchi, F.; Breitenlechner, M.; et al. Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere. Nature 2013, 502 (7471), 359−363. (16) Hazra, M. K.; Sinha, A. Formic acid catalyzed hydrolysis of SO3 in the gas phase: a barrierless mechanism for sulfuric acid production of potential atmospheric importance. J. Am. Chem. Soc. 2011, 133 (43), 17444−53. (17) Torrent-Sucarrat, M.; Francisco, J. S.; Anglada, J. M. Sulfuric acid as autocatalyst in the formation of sulfuric acid. J. Am. Chem. Soc. 2012, 134 (51), 20632. (18) Temelso, B.; Morrell, T. E.; Shields, R. M.; Allodi, M. A.; Wood, E. K.; Kirschner, K. N.; Castonguay, T. C.; Archer, K. A.; Shields, G. C. Quantum mechanical study of sulfuric acid hydration: atmospheric implications. J. Phys. Chem. A 2012, 116 (9), 2209. (19) Husar, D. E.; Temelso, B.; Ashworth, A. L.; Shields, G. C. Hydration of the Bisulfate Ion: Atmospheric Implications. J. Phys. Chem. A 2012, 116 (21), 5151−5163. (20) Liu, J.; Fang, S.; Liu, W.; Wang, M.; Tao, F. M.; Liu, J. Y. Mechanism of the gaseous hydrolysis reaction of SO2: Effects of NH3 versus H2O. J. Phys. Chem. A 2015, 119 (1), 102−11. (21) Li, L.; Kumar, M.; Zhu, C.; Zhong, J.; Francisco, J. S.; Zeng, X. C. Near-Barrierless Ammonium Bisulfate Formation via a LoopStructure Promoted Proton Transfer Mechanism on the Surface of Water. J. Am. Chem. Soc. 2016, 138 (6), 1816−1819. (22) Bai, X.-M.; Li, M. Test of classical nucleation theory via molecular-dynamics simulation. J. Chem. Phys. 2005, 122 (22), 224510. (23) Vehkamäki, H.; Riipinen, I. Thermodynamics and kinetics of atmospheric aerosol particle formation and growth. Chem. Soc. Rev. 2012, 41 (15), 5160−5173. (24) Zakharov, V. V.; Brodskaya, E. N.; Laaksonen, A. Surface tension of water droplets: A molecular dynamics study of model and size dependencies. J. Chem. Phys. 1997, 107 (24), 10675−10683. (25) Hua, W.; Verreault, D.; Allen, H. C. Relative Order of Sulfuric Acid, Bisulfate, Hydronium, and Cations at the Air−Water Interface. J. Am. Chem. Soc. 2015, 137 (43), 13920−13926. (26) Skinner, L. M.; Sambles, J. R. The Kelvin equationa review. J. Aerosol Sci. 1972, 3 (3), 199−210. (27) Tolman, R. C. The Effect of Droplet Size on Surface Tension. J. Chem. Phys. 1949, 17 (3), 333−337. (28) Li, X.; Hede, T.; Tu, Y.; Leck, C.; Ågren, H. Surface-Active cisPinonic Acid in Atmospheric Droplets: A Molecular Dynamics Study. J. Phys. Chem. Lett. 2010, 1 (4), 769−773.

Computational methods, detailed structural and energetic data, radial number densities, free energies of solvation, vapor pressure results, and nucleation rates (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (H.L.). *E-mail: [email protected] (X.C.Z.). *E-mail: [email protected] (D.C.). ORCID

Daojian Cheng: 0000-0001-7977-0750 Xiao Cheng Zeng: 0000-0003-4672-8585 Hui Li: 0000-0002-1725-6796 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS H.L. acknowledges funding support from National Natural Science Foundation of China (21773005). The computational resources utilized in this research were provided by Shanghai Supercomputer Center.

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REFERENCES

(1) Kulmala, M.; Kontkanen, J.; Junninen, H.; Lehtipalo, K.; Manninen, H. E.; Nieminen, T.; Petäjä, T.; Sipilä, M.; Schobesberger, S.; Rantala, P.; et al. Direct observations of atmospheric aerosol nucleation. Science 2013, 339 (6122), 943−946. (2) Bianchi, F.; Tröstl, J.; Junninen, H.; Frege, C.; Henne, S.; Hoyle, C. R.; Molteni, U.; Herrmann, E.; Adamov, A.; Bukowiecki, N.; et al. New particle formation in the free troposphere: A question of chemistry and timing. Science 2016, 352 (6289), 1109. (3) Zhang, R.; Khalizov, A.; Wang, L.; Hu, M.; Xu, W. Nucleation and growth of nanoparticles in the atmosphere. Chem. Rev. 2012, 112 (3), 1957−2011. (4) Kaufman, Y. J.; Tanré, D.; Boucher, O. A satellite view of aerosols in the climate system. Nature 2002, 419 (6903), 215−223. (5) Tang, M.; Cziczo, D. J.; Grassian, V. H. Interactions of Water with Mineral Dust Aerosol: Water Adsorption, Hygroscopicity, Cloud Condensation, and Ice Nucleation. Chem. Rev. 2016, 116 (7), 4205− 4259. (6) Kerminen, V.-M.; Paramonov, M.; Anttila, T.; et al. Cloud condensation nuclei production associated with atmospheric nucleation: a synthesis based on existing literature and new results. Atmos. Chem. Phys. 2012, 12 (24), 12037−12059. (7) Petters, M. D.; Kreidenweis, S. M. A single parameter representation of hygroscopic growth and cloud condensation nucleus activity. Atmos. Chem. Phys. 2007, 7 (8), 1961−1971. (8) Lee, A. K. Y.; Ling, T. Y.; Chan, C. K. Understanding hygroscopic growth and phase transformation of aerosols using single particle Raman spectroscopy in an electrodynamic balance. Faraday Discuss. 2008, 137 (0), 245−263. (9) Zhang, R. Atmospheric science. Getting to the critical nucleus of aerosol formation. Science 2010, 328 (5984), 1366−1367. (10) Sipilä, M.; Berndt, T.; Petäjä, T.; Brus, D.; Vanhanen, J.; Stratmann, F.; Patokoski, J.; Hyvärinen, A. P.; Lihavainen, H. The role of sulfuric acid in atmospheric nucleation. Science 2010, 327, 1243. (11) Kirkby, J.; Curtius, J.; Almeida, J.; Dunne, E.; Duplissy, J.; Ehrhart, S.; Franchin, A.; Gagné, S.; Ickes, L.; Kürten, A.; Kupc, A.; Metzger, A.; Riccobono, F.; Rondo, L.; Schobesberger, S.; Tsagkogeorgas, G.; Wimmer, D.; Amorim, A.; Bianchi, F.; Breitenlechner, M.; David, A.; Dommen, J.; Downard, A.; Ehn, M.; Flagan, R. C.; Haider, S.; Hansel, A.; Hauser, D.; Jud, W.; Junninen, H.; Kreissl, F.; Kvashin, A.; Laaksonen, A.; Lehtipalo, K.; Lima, J.; Lovejoy, E. R.; Makhmutov, V.; Mathot, S.; Mikkilä, J.; Minginette, P.; 1131


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The Journal of Physical Chemistry Letters (29) Hyvärinen, A. P.; Raatikainen, T.; Laaksonen, A.; Viisanen, Y.; Lihavainen, H. Surface tensions and densities of H2SO4 + NH3 + water solutions. Geophys. Res. Lett. 2005, 32 (16), 16806. (30) Vehkamäki, H.; Kulmala, M.; Napari, I.; Lehtinen, K. E. J.; Timmreck, C.; Noppel, M.; Laaksonen, A. An improved parameterization for sulfuric acid−water nucleation rates for tropospheric and stratospheric conditions. J. Geophys. Res. 2002, 107 (D22), AAC 3-1− AAC 3-10. (31) Hämeri, K.; Väkevä, M.; Hansson, H.-C.; Laaksonen, A. Hygroscopic growth of ultrafine ammonium sulphate aerosol measured using an ultrafine tandem differential mobility analyzer. J. Geophys. Res-Atmos 2000, 105 (D17), 22231−22242. (32) Li, X.; Hede, T.; Tu, Y.; Leck, C.; Ågren, H. Glycine in aerosol water droplets: a critical assessment of K hler theory by predicting surface tension from molecular dynamics simulations. Atmos. Chem. Phys. 2011, 11 (2), 519−527. (33) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R. Gaussian 03, revision C. 02; Gaussian: Wallingford, CT,2004. (34) Cannon, W.; Pettitt, B. M.; McCammon, J. A. Sulfate Anion in Water: Model Structural, Thermodynamic, and Dynamic Properties. J. Phys. Chem. 1994, 98, 6225−6230. (35) Marcus, Y. Ion Solvation; Wiley: 1985. (36) Boudon, S.; Wipff, G. Free energy calculations involving NH4+ in water. J. Comput. Chem. 1991, 12 (1), 42−51. (37) Koyano, Y.; Takenaka, N.; Nakagawa, Y.; Nagaoka, M. On the Importance of Lennard−Jones Parameter Calibration in QM/MM Framework: Reaction Path Tracing via Free Energy Gradient Method for Ammonia Ionization Process in Aqueous Solution. Bull. Chem. Soc. Jpn. 2010, 83 (5), 486−494. (38) Zhang, Y. H.; Chan, C. K. Study of Contact Ion Pairs of Supersaturated Magnesium Sulfate Solutions Using Raman Scattering of Levitated Single Droplets. J. Phys. Chem. A 2000, 104 (40), 9191− 9196. (39) Eguchi, N.; Shiotani, M. Intraseasonal variations of water vapor and cirrus clouds in the tropical upper troposphere. J. Geophys. Res. 2004, 109 (D12), D12106. (40) Ewart, H. A.; Hyde, K. E. The water drop experiment: Determining the surface tension of a liquid by automating the dropweight method. J. Chem. Educ. 1992, 69 (10), 814−815. (41) Yu, F.; Turco, R. P. Ultrafine aerosol formation via ionmediated nucleation. Geophys. Res. Lett. 2000, 27 (6), 883−886. (42) Manninen, H. E.; Nieminen, T.; Riipinen, I.; Ylijuuti, T. Charged and total particle formation and growth rates during EUCAARI 2007 campaign in Hyytiälä. Atmos. Chem. Phys. 2009, 9 (12), 4077−4089.

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