A theoretical study of hydrated molecular clusters of amines and dicarboxylic acids

Direct Measurements of Covalently Bonded Sulfuric Anhydrides from Gas-Phase Reactions of SO3 with Acids under Ambient Conditions

Sulfur trioxide (SO3) is an important oxide of sulfur and a key intermediate in the formation of sulfuric acid (H2SO4, SA) in the Earth's atmosphere. This conversion to SA occurs rapidly due to the reaction of SO3 with a water dimer. However, gas-phase SO3 has been measured directly at concentrations that are comparable to that of SA under polluted mega-city conditions, indicating gaps in our current understanding of the sources and fates of SO3. Its reaction with atmospheric acids could be one such fate that can have significant implications for atmospheric chemistry. In the present investigation, laboratory experiments were conducted in a flow reactor to generate a range of previously uncharacterized condensable sulfur-containing reaction products by reacting SO3 with a set of atmospherically relevant inorganic and organic acids at room temperature and atmospheric pressure. Specifically, key inorganic acids known to be responsible for most ambient new particle formation events, iodic acid (HIO3, IA) and SA, are observed to react promptly with SO3 to form iodic sulfuric anhydride (IO3SO3H, ISA) and disulfuric acid (H2S2O7, DSA). Carboxylic sulfuric anhydrides (CSAs) were observed to form by the reaction of SO3 with C2 and C3 monocarboxylic (acetic and propanoic acid) and dicarboxylic (oxalic and malonic acid)-carboxylic acids. The formed products were detected by a nitrate-ion-based chemical ionization atmospheric pressure interface time-of-flight mass spectrometer (NO3--CI-APi-TOF; NO3--CIMS). Quantum chemical methods were used to compute the relevant SO3 reaction rate coefficients, probe the reaction mechanisms, and model the ionization chemistry inherent in the detection of the products by NO3--CIMS. Additionally, we use NO3--CIMS ambient data to report that significant concentrations of SO3 and its acid anhydride reaction products are present under polluted, marine and polar, and volcanic plume conditions. Considering that these regions are rich in the acid precursors studied here, the reported reactions need to be accounted for in the modeling of atmospheric new particle formation.

Roles of Amides on the Formation of Atmospheric HONO and the Nucleation of Nitric Acid Hydrates

Nitrous acid (HONO) is hazardous to the human respiratory system, and the hydrolysis of NO₂ is the source of HONO. Hence, the investigation on the removal and transformation of HONO is urgently established. The effects of amide on the mechanism and kinetics of the formation of HONO with acetamide, formamide, methylformamide, urea, and its clusters of the catalyst were studied theoretically. The results show that amide and its small clusters reduce the energy barrier, the substituent improves the catalytic efficiency, and the catalytic effect order is dimer > monohydrate > monomer. Meanwhile, the clusters composed of nitric acid (HNO₃), amides, and 1-6 water molecules were investigated in the amide-assisted nitrogen dioxide (NO₂) hydrolysis reaction after HONO decomposes by combining the system sampling technique and density functional theory. The study on thermodynamics, intermolecular forces, optics properties of the clusters, as well as the influence of humidity, temperature, atmospheric pressure, and altitude shows that amide molecules promote the clustering and enhance the optical properties. The substituent facilitates the clustering of amide and nitric acid hydrate and lowers the humidity sensitivity of the clusters. The findings will help to control the atmospheric aerosol particle and then reduce the harm of poisonous organic chemicals on human health.

Current and future machine learning approaches for modeling atmospheric cluster formation

The formation of strongly bound atmospheric molecular clusters is the first step towards forming new aerosol particles. Recent advances in the application of machine learning models open an enormous opportunity for complementing expensive quantum chemical calculations with efficient machine learning predictions. In this Perspective, we present how data-driven approaches can be applied to accelerate cluster configurational sampling, thereby greatly increasing the number of chemically relevant systems that can be covered.

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.

Interaction of Glutamic Acid/Protonated Glutamic Acid with Amide and Water Molecules: A Theoretical Study

Amino acids are important nitrogen-containing compounds and organic carbon components that exist widely in the atmosphere. The formation of atmospheric aerosols is affected by their interactions with amides. The dimers formed by glutamic acid (Glu) or protonated glutamic acid (Glu⁺) with three kinds of amide molecules (formamide FA, acetamide AA, urea U) and the hydrated clusters formed by Glu or Glu⁺, U molecules along with one to six water molecules were systematically studied at the M06-2X/6-311++G(3df,3pd) level. U is predicted to form a more stable structure with Glu/Glu⁺ than FA and AA by thermodynamics. If the concentration ratio of FA to U is less than 10⁴, U will play a critical role in NPF. The degree of hydration in Glu⁺-mU-nW is higher than that of Glu-mU-nW (m = 0, 1; n = 0-6) clusters. Notably, Glu contributes more to the Rayleigh scattering properties than glutaric acid and sulfuric acid, and thus may lead to the destruction of atmospheric visibility. This study is helpful to better understand the properties of organic aerosols containing amino acids or amides.

Bridged-ozonolysis of mixed aromatic hydrocarbons and organic amines: Inter-inhibited decay rate, altered product yield and synergistic-effect-enhanced secondary organic aerosol formation

Ozonolysis of aromatic hydrocarbons (AHs) or organic amines (OAs) occurs via different transformation processes, with varying rate constants and contributions to secondary organic aerosol (SOA) formation. However, to date no data is available on the ozonolysis of mixtures of AHs and OAs. This study investigated the kinetics, products and SOA yield from ozonolysis of mixture of trimethylamine with styrene, toluene or m-xylene. In the mixed system, the decay rates of styrene and trimethylamine were (1.32 ± 0.26) × 10^-4 s^-1 and (0.80 ± 0.02) × 10^-4 s^-1, decreasing up to 36.5 % and 54.4 % compared with their respective individual systems. This inter-inhibition of decay rates increased the yield of main products from styrene (i.e. benzaldehyde) by 23.5 % and trimethylamine (i.e. nitromethane) by 346.4 %. Ozonolysis of styrene or trimethylamine produced formaldehyde, which acted as a bridged product connecting the ozonolysis pathways of these two substrates, altering the yields of all products. Ozonolysis of styrene to benzaldehyde determined the increase of SOA particle number concentration (from 9.5 × 10⁵ to 1.9 × 10⁶ particles cm^-3), while trimethylamine ozonolysis to N, N-dimethylformamide contributed to synergistic-effect-enhanced SOA yield (from (64.3 ± 3.5)% to (68.1 ± 4.8)%). The findings provide a novel insight into the kinetics and mechanism of ozonolysis, as well as the resulting SOA formation from mixtures of AHs and OAs, helping to comprehensively understand the transformation and fate of organics in real atmospheric environments.

Theoretical analysis of sulfuric acid–dimethylamine–oxalic acid–water clusters and implications for atmospheric cluster formation

In recent years, organic compounds potentially involved in atmospheric particle formation have received increased attention. However, the contributions of organic acids as precursors in nucleation remain ambiguous. In this study, the low-lying structures and thermodynamics of the sulfuric acid–dimethylamine–oxalic acid–water system are obtained at the M06-2X/6-311+G(2d,p) level, and the single point energy of the clusters has been calculated at the DF-LMP2-F12/VDZ-F12 level. The formations of the multicomponent clusters are predicted based on thermodynamics, involving proton transfer and hydrogen bonding interactions. Oxalic acid can synergistically promote the formation of the sulfuric acid–dimethylamine–oxalic acid–water system while inhibiting this with the addition of more sulfuric acid molecules. The results of hydrate distribution show that un-hydrate clusters play a dominant role during formation. Moreover, dimethylamine and oxalic acid have similar effects on Rayleigh scattering properties, and the clusters involving complex mixtures of compounds can have high optical activities.

The structure of SA₂.DMA.OA.W₄ cluster.

The potential mechanism of atmospheric new particle formation involving amino acids with multiple functional groups

Amino acids are recognized as significant components of atmospheric aerosols. However, their potential role in atmospheric new particle formation (NPF) is poorly understood, especially aspartic acid (ASP), one of the most abundant amino acids in the atmosphere. It has not only two advantageous carboxylic acid groups but also one amino group, both of which are both effective groups enhancing NPF. Herein, the participation mechanism of ASP in the formation of new particle involving sulfuric acid (SA)-ammonia (A)-based system has been studied using the Density Functional Theory (DFT) combined with the Atmospheric Clusters Dynamic Code (ACDC). The results show that the addition of ASP molecules in the SA-A-based clusters provides a promotion on the interaction between SA and A molecules. Moreover, ACDC simulations indicate that ASP could present an obvious enhancement effect on SA-A-based cluster formation rates. Meanwhile, the enhancement strength R presents a positive dependence on [ASP] and a negative dependence on [SA] and [A]. Besides, the enhancement effect of ASP is compared with that of malonic acid (MOA) with two carboxylic acid groups (Chemosphere, 2018, 203, 26-33), and ASP presents a more obvious enhancement effect than MOA. The mechanism of NPF indicates that ASP could contribute to cluster formation as a "participator" which is different from the "catalytic" role of MOA at 238 K. These new insights are helpful to understand the mechanism of NPF involving organic compounds with multiple functional groups, especially the abundant amino acids, such as the ASP, in the urban/suburban areas with intensive human activities and industrial productions and therefore the abundant sources of amino acids. Furthermore, the NPF of the SA-A-based system involving amino acid should be considered when assessing the environmental risk of amino acid.

Explosive Secondary Aerosol Formation during Severe Haze in the North China Plain

Severe haze events with exceedingly high-levels of fine aerosols occur frequently over the past decades in the North China Plain (NCP), exerting profound impacts on human health, weather, and climate. The development of effective mitigation policies requires a comprehensive understanding of the haze formation mechanisms, including identification and quantification of the sources, formation, and transformation of the aerosol species. Haze evolution in this region exhibits distinct physical and chemical characteristics from clean to polluted periods, as evident from increasing stagnation and relative humidity, but decreasing solar radiation as well as explosive secondary aerosol formation. The latter is attributed to highly elevated concentrations of aerosol precursor gases and is reflected by rapid increases in the particle number and mass concentrations, both corresponding to nonequilibrium chemical processes. Considerable new knowledge has been acquired to understand the processes regulating haze formation, particularly in light of the progress in elucidating the aerosol formation mechanisms. This review synthesizes recent advances in understanding secondary aerosol formation, by highlighting several critical chemical/physical processes, that is, new particle formation and aerosol growth driven by photochemistry and aqueous chemistry as well as the interaction between aerosols and atmospheric stability. Current challenges and future research priorities are also discussed.

A theoretical study of hydrogen-bonded molecular clusters of sulfuric acid and organic acids with amides

Amides, a series of significant atmospheric nitrogen-containing volatile organic compounds (VOCs), can participate in new particle formation (NPF) throught interacting with sulfuric acid (SA) and organic acids. In this study, we investigated the molecular interactions of formamide (FA), acetamide (AA), N-methylformamide (MF), propanamide (PA), N-methylacetamide (MA), and N,N-dimethylformamide (DMF) with SA, acetic acid (HAC), propanoic acid (PAC), oxalic acid (OA), and malonic acid (MOA). Global minimum of clusters were obtained through the association of the artificial bee colony (ABC) algorithm and density functional theory (DFT) calculations. The conformational analysis, thermochemical analysis, frequency analysis, and topological analysis were conducted to determine the interactions of hydrogen-bonded molecular clusters. The heterodimers formed a hepta or octa membered ring through four different types of hydrogen bonds, and the strength of the bonds are ranked in the following order: SOH•••O > COH•••O > NH•••O > CH•••O. We also evaluated the stability of the clusters and found that the stabilization effect of amides with SA is weaker than that of amines with SA but stronger than that of ammonia (NH₃) with SA in the dimer formation of nucleation process. Additionally, the nucleation capacity of SA with amides is greater than that of organic acids with amides.

Atmospherically Relevant Hydrogen-Bonded Interactions between Methanesulfonic Acid and H2SO4 Clusters: A Computational Study

A detailed and systematic quantum-chemical calculation has been performed with high-level density functional theory (DFT) to analyze the electrostatic interaction of methanesulfonic acid (CH₃SO₃H), also known as MSA, with pre-formed clusters of sulfuric acid (H₂SO₄) molecules in ambient conditions. Both MSA and H₂SO₄ are considered as atmospheric molecules that might play active roles in aerosol formation. The interactions between MSA and H₂SO₄ clusters lead to the formation of MSA···(H₂SO₄)_n (n = 2, 3) complexes stabilized by the formation of different types of intermolecular hydrogen bond networks. Analyses of cluster binding energies and free energy changes associated with their formation indicate that MSA could bring additional stability into the atmospheric molecular clusters responsible for aerosol formation. Variations of Gibbs free energy with temperature and pressure have been analyzed. The lower temperatures and pressures at the higher altitudes of the troposphere are found to play in favor of higher stability of the MSA···(H₂SO₄)_n clusters. Effects of hydrogen bond formation on dipole moment, mean polarizability, and anisotropy of polarizability of the clusters have been analyzed. Rayleigh scattering intensities are found to increase many-fold when light interacts with the MSA···(H₂SO₄)_n clusters.

Methanesulfonic Acid-driven New Particle Formation Enhanced by Monoethanolamine: A Computational Study

Amines are recognized as significant enhancing species on methanesulfonic acid (MSA)-driven new particle formation (NPF). Monoethanolamine (MEA) has been detected in the atmosphere, and its concentration could be significantly increased once MEA-based postcombustion CO₂ capture technology is widely implemented. Here, we evaluated the enhancing potential of MEA on MSA-driven NPF by examining the formation of MEA-MSA clusters using a combination of quantum chemical calculations and kinetics modeling. The results indicate that the -OH group of MEA can form at least one hydrogen bond with MSA or MEA in all MEA-containing clusters. The enhancing potential of MEA is higher than that of the strongest enhancing agent known so far, methylamine (MA), for MSA-driven NPF. Such high enhancing potential can be ascribed to not only the higher gas-phase basicity but also the role of the additional -OH group of MEA in increasing the binding free energy by forming additional hydrogen bonds. This clarifies the importance of hydrogen-bonding capacity from the nonamino group of amines in enhancing MSA-driven NPF. The main growth pathway for MEA-MSA clusters proceeds via the initial formation of the (MEA)₁(MSA)₁ cluster, followed by alternately adding one MSA and one MEA molecule, differing from the case of MA-MSA clusters.

A molecular understanding of the interaction of typical aromatic acids with common aerosol nucleation precursors and their atmospheric implications

Aromatic acids, which are generated from numerous anthropogenic emissions and secondary transformations, have been considered to play a crucial role in new particle formation. In this study, we performed theoretical calculations at the PW91PW91/6-311++G(3df,3pd) level to investigate the interaction between typical aromatic acids namely benzoic acid (BA), phenylacetic acid (PAA), phthalic acid (PA), isophthalic acid (mPA), and terephthalic acid (PTA) and common atmospheric nucleation precursors namely sulfuric acid (SA), water (H2O), ammonia (NH3), methylamine (MA), dimethylamine (DMA), and trimethylamine (TMA). The geometric analysis, Gibbs free energy analysis, OH/NH-stretching vibrational frequency calculation, and atoms in molecules (AIM) analysis were conducted to determine the interactions in the complexes. The heterodimers formed a six to eight membered ring through four types of hydrogen bond, and the bond strength could be ranked in descending order: SO-H⋯O > O-H⋯O/N > N-H⋯O. The BA/PAA/mPA/PTA-SA complexes had the lowest Gibbs free energy values. PA was more likely to interact with NH3 or amines rather than SA due to an intra-molecular hydrogen bond. Additionally, the aromatic acids have similar ability to interact with SA and NH3 as monocarboxylic/dicarboxylic acid. The formation potential of the heterodimers from aromatic acids with common nucleation precursors in ambient atmosphere was investigated.

Thermal Stability of Particle-Phase Monoethanolamine Salts

The use of monoethanolamine (MEA, 2-hydroxyethanamine) for scrubbing of carbon dioxide from combustion flue gases may become the dominant technology for carbon capture in the near future. The widespread implementation of this technology will result in elevated emissions of MEA to the environment that may increase the loading and modify the properties of atmospheric aerosols. We have utilized experimental measurements together with aerosol microphysics calculations to derive thermodynamic properties of several MEA salts, potentially the dominant forms of MEA in atmospheric particles. The stability of the salts was found to depend strongly on the chemical nature of the acid counterpart. The saturation vapor pressures and vaporization enthalpies obtained in this study can be used to evaluate the role of MEA in the aerosol and haze formation, helping to assess impacts of the MEA-based carbon capture technology on air quality and climate change.

A density functional theory study of aldehydes and their atmospheric products participating in nucleation

The products of aldehydes from aldol condensation, hydration, and polymerization reactions can promote new particle formation by stabilizing sulfuric acid.

Gas-phase hydration of glyoxylic acid: Kinetics and atmospheric implications

Oxocarboxylic acids are one of the most important organic species found in secondary organic aerosols and can be detected in diverse environments. But the hydration of oxocarboxylic acids in the atmosphere has still not been fully understood. Neglecting the hydration of oxocarboxylic acids in atmospheric models may be one of the most important reasons for the significant discrepancies between field measurements and abundance predictions of atmospheric models for oxocarboxylic acids. In the present paper, glyoxylic acid, as the most abundant oxocarboxylic acids in the atmosphere, has been selected as an example to study whether the hydration process can occur in the atmosphere and what the kinetic process of hydration is. The gas-phase hydration of glyoxylic acid to form the corresponding geminal diol and those catalyzed by atmospheric common substances (water, sulfuric acid and ammonia) have been investigated at the CCSD(T)-F12/cc-pVDZ-F12//M06-2X/6-311++G(3df,3pd) level of theory. The contour map of electron density difference of transition states have been further analyzed. It is indicated that these atmospheric common substances can all catalyze on the hydration to some extent and sulfuric acid is the most effective reducing the Gibbs free energy of activation to 9.48 kcal/mol. The effective rate constants combining the overall rate constants and concentrations of the corresponding catalysts have shown that water and sulfuric acid are both important catalysts and the catalysis of sulfuric acid is the most effective for the gas-phase hydration of glyoxylic acid. This catalyzed processes are potentially effective in coastal regions and polluted regions.

Chemical Characterization of Gas- and Particle-Phase Products from the Ozonolysis of α-Pinene in the Presence of Dimethylamine

Amines are recognized as key compounds in new particle formation (NPF) and secondary organic aerosol (SOA) formation. In addition, ozonolysis of α-pinene contributes substantially to the formation of biogenic SOAs in the atmosphere. In the present study, ozonolysis of α-pinene in the presence of dimethylamine (DMA) was investigated in a flow tube reactor. Effects of amines on SOA formation and chemical composition were examined. Enhancement of NPF and SOA formation was observed in the presence of DMA. Chemical characterization of gas- and particle-phase products by high-resolution mass spectrometric techniques revealed the formation of nitrogen containing compounds. Reactions between ozonolysis reaction products of α-pinene, such as pinonaldehyde or pinonic acid, and DMA were observed. Possible reaction pathways are suggested for the formation of the reaction products. Some of the compounds identified in the laboratory study were also observed in aerosol samples (PM₁) collected at the SMEAR II station (Hyytiälä, Finland) suggesting that DMA might affect the ozonolysis of α-pinene in ambient conditions.

The Role of Oxalic Acid in New Particle Formation from Methanesulfonic Acid, Methylamine, and Water

Atmospheric particles are notorious for their effects on human health and visibility and are known to influence climate. Though sulfuric acid and ammonia/amines are recognized as main contributors to new particle formation (NPF), models and observations have indicated that other species may be involved. It has been shown that nucleation from methanesulfonic acid (MSA) and amines, which is enhanced with added water, can also contribute to NPF. While organics are ubiquitous in air and likely to be involved in NPF by stabilizing small clusters for further growth, their effects on the MSA-amine system are not known. This work investigates the effect of oxalic acid (OxA) on NPF from the reaction of MSA and methylamine (MA) at 1 atm and 294 K in the presence and absence of water vapor using an aerosol flow reactor. OxA and MA do not efficiently form particles even in the presence of water, but NPF is enhanced when adding MSA to OxA-MA with and without water. The addition of OxA to MSA-MA mixtures yields a modest NPF enhancement, whereas the addition of OxA to MSA-MA-H₂O has no effect. Possible reasons for these effects are discussed.

Particle formation and growth from oxalic acid, methanesulfonic acid, trimethylamine and water: a combined experimental and theoretical study

A combined experimental-theoretical study on the effect of oxalic acid on particle formation and growth from the reaction of MSA with trimethylamine in the absence and presence of water.

Interaction of oxalic acid with dimethylamine and its atmospheric implications

Oxalic acid and dimethylamine are the most common organic acid and base in the atmosphere, and are recognized as significant precursor species in atmospheric new particle formation.

Hydrogen Bonding Interaction between Atmospheric Gaseous Amides and Methanol

Amides are important atmospheric organic–nitrogen compounds. Hydrogen bonded complexes of methanol (MeOH) with amides (formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide and N,N-dimethylacetamide) have been investigated. The carbonyl oxygen of the amides behaves as a hydrogen bond acceptor and the NH group of the amides acts as a hydrogen bond donor. The dominant hydrogen bonding interaction occurs between the carbonyl oxygen and the OH group of methanol as well as the interaction between the NH group of amides and the oxygen of methanol. However, the hydrogen bonds between the CH group and the carbonyl oxygen or the oxygen of methanol are also important for the overall stability of the complexes. Comparable red shifts of the C=O, NH- and OH-stretching transitions were found in these MeOH–amide complexes with considerable intensity enhancement. Topological analysis shows that the electron density at the bond critical points of the complexes fall in the range of hydrogen bonding criteria, and the Laplacian of charge density of the O–H∙∙∙O hydrogen bond slightly exceeds the upper value of the Laplacian criteria. The energy decomposition analysis further suggests that the hydrogen bonding interaction energies can be mainly attributed to the electrostatic, exchange and dispersion components.

Effects of Global and Local Anharmonicities on the Thermodynamic Properties of Sulfuric Acid Monohydrate

We use state-of-the-art electronic structure calculation methods and large basis sets to obtain reliable values for the thermodynamic properties of sulfuric acid monohydrate and study the effects of vibrational anharmonicity on these properties. We distinguish between two forms of vibrational anharmonicity: local anharmonicity, which refers to the anharmonicity of the vibrational modes of a given cluster conformer, and global anharmonicity, which originates from accounting for the presence of different conformers in the first place. In our most accurate approach, we solve the nuclear Schrödinger equation variationally for the intermolecular large-amplitude motions, thus quantum-mechanically accounting for the presence of higher-energy conformers for both reactants and products, while using the standard vibrational perturbational approach for the other vibrational modes. This results in a value of -11.0 kJ/mol for the reaction Gibbs free energy at 298.15 K. When standard vibrational perturbational approaches are employed, the effects of local anharmonicity depend heavily on the choice of the electronic structure calculation basis set. In fact, better results can often be achieved by combining a simple harmonic treatment for the vibrational partition function with a statistical mechanical accounting of global anharmonicity. Thus, we recommend that future studies that intend to include anharmonicity start by accounting for the presence of higher-energy conformers and only then consider whether local anharmonicity calculations are feasible and necessary.

Quantitative analysis of aliphatic amines in urban aerosols based on online derivatization and high performance liquid chromatography

A method combining online derivatization with high performance liquid chromatography/fluorescence detection was developed for the determination of seven aliphatic amines (ethanolamine, methylamine, ethylamine, propylamine, butylamine, pentylamine and hexylamine) in urban aerosols. The collected amines were online derivatized with o-phthalaldehyde to form highly fluorescent sulfonatoisoindole derivatives. The derivatives were completely separated in 13 min through gradient elution and detected by fluorescence detection at an excitation wavelength of 334 nm and an emission wavelength of 443 nm. Under the optimized conditions, the relative standard derivations (RSDs) of all detected amines were 0.02-2.03% and 1.04-1.52% for the retention time and peak area, respectively. Excellent linearity was achieved for each analyte, ranging from 5 μg L(-1) to 1000 μg L(-1) (R(2) > 0.99). The detection limits for all analytes were below 1.1 μg L(-1). The proposed method was used to analyze aliphatic amines in 35 samples of urban PM2.5 collected in Shanghai and was found to be suitable for the determination of particulate aliphatic amines at ng m(-3) levels in ambient air. Based on our measurements, ethanolamine and methylamine were the most abundant species on average in Shanghai during dry and wet seasons. The highest concentration was 15.3 ng m(-3) for ethanolamine and 13.2 ng m(-3) for methylamine.

Hygroscopic Characteristics of Alkylaminium Carboxylate Aerosols

The hygroscopic growth factor (HGF) and cloud condensation nuclei (CCN) activity for a series of alkylaminium carboxylate aerosols have been measured using a hygroscopicity tandem differential mobility analyzer coupled to a condensation particle counter and a CCN counter. The particles, consisting of the mixtures of mono- (acetic, propanoic, p-toluic, and cis-pinonic acid) and dicarboxylic (oxalic, succinic, malic, adipic, and azelaic acid) acid with alkylamine (mono-, di-, and trimethylamines), represent those commonly found under diverse environmental conditions. The hygroscopicity parameter (κ) of the alkylaminium carboxylate aerosols was derived from the HGF and CCN results and theoretically calculated. The HGF at 90% RH is in the range of 1.3 to 1.8 for alkylaminium monocarboxylates and 1.1 to 2.2 for alkylaminium dicarboxylates, dependent on the molecular functionality (i.e., the carboxylic or OH functional group in organic acids and methyl substitution in alkylamines). The κ value for all alkylaminium carboxylates is in the range of 0.06-1.37 derived from the HGF measurements at 90% RH, 0.05-0.49 derived from the CCN measurements, and 0.22-0.66 theoretically calculated. The measured hygroscopicity of the alkylaminium carboxylates increases with decreasing acid to base ratio. The deliquescence point is apparent for several of the alkylaminium dicarboxylates but not for the alkylaminium monocarboxylates. Our results reveal that alkylaminium carboxylate aerosols exhibit distinct hygroscopic and deliquescent characteristics that are dependent on their molecular functionality, hence regulating their impacts on human health, air quality, and direct and indirect radiative forcing on climate.

Characterization of the nucleation precursor (H2SO4–(CH3)2NH) complex: intra-cluster interactions and atmospheric relevance

Amines have been proposed to participate in the nucleation process, but the electron density analysis and the determination of a temperature dependence of the clusters are still lacking.

New particle formation and growth from methanesulfonic acid, trimethylamine and water

Water participates in the formation of initial clusters to enhance particle formation from methanesulfonic acid and trimethylamine.

Rayleigh light scattering properties of atmospheric molecular clusters consisting of sulfuric acid and bases

The Rayleigh light scattering properties of (H₂SO₄)_a(NH₃)_b and (H₂SO₄)_a((CH₃)₂NH)_b atmospheric molecular clusters have been investigated using a response theory approach.

On the properties and atmospheric implication of amine-hydrated clusters

Amines have been recognized as important precursor species in the formation of new atmospheric particles.

Deciphering the scaling of single-molecule interactions using Jarzynski's equality

Unravelling the complexity of the macroscopic world relies on understanding the scaling of single-molecule interactions towards integral macroscopic interactions. Here, we demonstrate the scaling of single acid-amine interactions through a synergistic experimental approach combining macroscopic surface forces apparatus experiments and single-molecule force spectroscopy. This experimental framework is ideal for testing the well-renowned Jarzynski's equality, which relates work performed under non-equilibrium conditions with equilibrium free energy. Macroscopic equilibrium measurements scale linearly with the number density of interfacial bonds, providing acid-amine interaction energies of 10.9 ± 0.2 kT. Irrespective of how far from equilibrium single-molecule experiments are performed, the Jarzynski's free energy converges to 11 ± 1 kT. Our results validate the applicability of Jarzynski's equality to unravel the scaling of non-equilibrium single-molecule experiments to scenarios where large numbers of molecules interacts simultaneously in equilibrium. The developed scaling strategy predicts large-scale properties such as adhesion or cell-cell interactions on the basis of single-molecule measurements.

Computational study of the Rayleigh light scattering properties of atmospheric pre-nucleation clusters

The Rayleigh and hyper Rayleigh scattering properties of the binary (H2SO4)(H2O)n and ternary (H2SO4)(NH3)(H2O)n clusters are investigated using a quantum mechanical response theory approach. The molecular Rayleigh scattering intensities are expressed using the dipole polarizability α and hyperpolarizability β tensors. Using density functional theory, we elucidate the effect of cluster morphology on the scattering properties using a combinatorial sampling approach. We find that the Rayleigh scattering intensity depends quadratically on the number of water molecules in the cluster and that a single ammonia molecule is able to induce a high anisotropy, which further increases the scattering intensity. The hyper Rayleigh scattering activities are found to be extremely low. This study presents the first attempt to map the scattering of atmospheric molecular clusters using a bottom-up approach.