Atmospheric Initial Nucleation Containing Carboxylic Acids

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.

Study of the Interactions between MeOH and Daidzein at the Molecular Level

In this study, the interactions between daidzein and methanol were studied to investigate isoflavone extraction. The complexes of MeOH-daidzein = 1:1, 2:1, 4:1, and 7:1 were studied using DFT/B3LYP-D3. According to the findings of this study, daidzein can act as a hydrogen bond donor as well as an acceptor. Binding energies demonstrate that more MeOH molecules interacting with daidzein could give more stability to the system. The strengths of the hydrogen bonds reveal that daidzein prefers to act as a hydrogen bond donor than an acceptor. The atoms in molecules (AIM) topological analysis was performed to analyze the nature of the hydrogen bonds. Moreover, daidzein, genistein, and glycitein are the most common soybean isoflavones, and their properties during extraction were also studied. The binding energies show that the soy isoflavone genistein is more reactive with the solvent than daidzein, followed by glycitein. The extraction conditions of the three common soy isoflavones in MeOH solution were obtained at 321, 328, and 348 K for genistein, daidzein, and glycitein, respectively. The generalized Kohn-Sham energy decomposition analysis (GKS-EDA) results indicate that the solute-solvent molecular interactions are typical hydrogen bonds with predominantly electrostatic and exchange energies in nature.

Tracing the biogenic secondary organic aerosol markers in rain, snow and hail

The molecular characterization of secondary organic aerosol (SOA) is based mainly on LC-MS analyses of particulate matter (PM) samples collected with aerosol samplers. Several studies have analyzed atmospheric waters, including rain and cloud water, for the presence of SOA components, however, no separation techniques were used making identification of the individual components in these complex mixtures impossible. We have applied our improved UHPLC-HR-MS methodology to analyze atmospheric precipitates (hailstone, rain and snow), as well as SOA collected with high-volume samplers. We achieved sensitivity levels and separation efficiencies that were sufficient for molecular-level identification of individual compounds. Tracing commonly known SOA markers such as organosulfates (OS), C₄-C₆ dicarboxylic acids and terpenoic acids revealed that the chromatographic profiles for both atmospheric precipitate and PM samples were very similar, with both giving similar component ratios, especially for OS. We also demonstrated that SOA markers can be detected directly from raw rain samples. Our results show that LC-MS techniques are suitable for the convenient analysis of atmospheric precipitates containing SOA markers at the molecular level. It complements traditional SOA analyses and provides additional sampling opportunities which will no doubt allow for better elucidation of chemical transformations of volatile organic compounds in the atmosphere.

Atmospheric implication of synergy in methanesulfonic acid–base trimers: a theoretical investigation

Synergy between molecules is ubiquitous in atmospheric clusters and significantly affects new particle formation (NPF). Herein, the effects of the synergy between base molecules on the stability and evaporation of MSA–X–Y (MSA = methanesulfonic acid; X, Y = ammonia (A), methylamine (M), or dimethylamine (D)) trimers were investigated via density functional theory (DFT) and the atmospheric clusters dynamic code (ACDC) method. The results show that proton transfer from MSA to X is exothermal and barrierless due to the synergy between X and Y molecules in MSA–X–Y trimers compared with MSA-X dimers. Cyclic hydrogen bonds are a typical characteristic of the stable trimers. Topological analysis using atoms in molecules (AIM) theory indicates that the electron density (ρ) and Laplacian of the electron density (∇²ρ) at the bond critical points (BCPs) in the trimers exceed the standard range of hydrogen bonds. The affinity for attaching a Y molecule to the MSA–X dimers and the substitution of Y₁ (Y = A and MA) by Y₂ (Y₂ = MA and DMA) in the MSA–X–Y trimers are thermodynamically spontaneous. In addition, the cyclic stabilization energy of the MSA–X–Y trimers increased as the alkalinities of X and Y increased. The total evaporation rate of the trimers decreased as the alkalinities of X and Y increased. Low temperature and high pressure significantly facilitate the formation of trimers. It is further confirmed that synergy plays an important role in atmospheric NPF events.

The effects of synergy of between X and Y on the stability of MSA–X–Y trimers were investigated via quantum chemical and kinetics simulation method.