Propionamide participating in H2SO4-based new particle formation: a theory study

Generation of 3-aminopropanamide and its cluster formation with nucleation precursors- a theoretical exploration

Aminoamides are formed in the atmospheric environments by the auto-oxidation of the parent diamines. In this work, the oxidation chemistry of diamine (1,3-Diaminopropane, Dap) to the amino amide (3- aminopropanamide, 3-APA) and its new particle formation potential with small atmospheric molecules such as NH3 (A), H2O (W) and H2SO4 (SA) are theoretically investigated using the M062X/6-311++G** theory. The bimolecular rate coefficient of the ·OH initiated H-atom abstraction is computed to be 1.01 × 10-11 cm3 molecule-1 s-1. Further reaction of the peroxy radical intermediate indicates that the pathway involving γ H- shift of the initially formed radical intermediates to be more favourable on kinetic grounds with the effective bimolecular rate coefficient of 3.87 × 10-14 cm3 molecule-1s-1. The thermodynamic barrier associated with the H-shifts involved in this pathway is in the range of 13-20 kcal/mol. The cluster formation of APA with SA is more favourable than the clusters with W and A, wherein the free energy of formation of (APA)(SA) and (APA)(SA)2 are -11.3 and -22.6 kcal/mol, respectively. However, the feasibility of cluster formation with W and A increases with the altitude and becomes spontaneous in the case of water at an altitude of 12 km. The present work indicates that aminoamides like 3-APA can participate in the initial stages of new particle formation events by forming clusters with SA molecules. The scattering parameters and topological analysis of different (Amide)(SA) clusters indicate more scattering properties for the (APA)(SA) cluster, which has an adverse effect on the atmosphere. Furthermore, topological analysis indicates that H-bond formation is more prominent in the (APA)(SA) cluster.

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.

Gas-phase catalytic hydration of I2O5 in the polluted coastal regions: Reaction mechanisms and atmospheric implications

Marine aerosols play an important role in the global aerosol system. In polluted coastal regions, ultra-fine particles have been recognized to be related to iodine-containing species and is more serious due to the impact of atmospheric pollutants. Many previous studies have identified iodine pentoxide (I₂O₅, IP) to be the key species in new particles formation (NPF) in marine regions, but the role of IP in the polluted coastal atmosphere is far to be fully understood. Considering the high humidity and concentrations of pollutants in the polluted coastal regions, the gas-phase hydration of IP catalyzed by sulfuric acid (SA), nitric acid (NA), dimethylamine (DMA), and ammonia (A) have been investigated at DLPNO-CCSD(T)//ωB97X-D/aug-cc-pVTZ + aug-cc-pVTZ-PP with ECP28MDF (for iodine) level of theory. The results show that the hydration of IP involves a significant energy barrier of 22.33 kcal/mol, while the pollutants SA, NA, DMA, and A all could catalyze the hydration of IP. Especially, with SA and DMA as catalysts, the hydration reactions of IP present extremely low barriers and high rate constants. It is suggested that IP is unstable under the catalysis of SA and DMA to generate iodic acid, which is the key component in NPF in marine regions. Thus, the catalytic hydration of IP is very likely to trigger the formation of iodine-containing particles. Our research provides a clear picture of the catalytic hydration of IP as well as theoretical guidance for NPF in the polluted coastal atmosphere.

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.

Organic acids could improve their nucleation ability through the cycloaddition reaction of SO₃ to generate corresponding carboxylic sulfuric anhydrides which may play a potential role in the atmospheric new particle formation.