Effect of Bisulfate, Ammonia, and Ammonium on the Clustering of Organic Acids and Sulfuric Acid

Abstract

We investigate the effect of the bisulfate anion HSO, ammonium cation NH, and ammonia NH on the clustering of sulfuric acid and pinic acid or 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA). The systems were chosen based on their expected relevance in atmospheric new particle formation. Using quantum chemical methods together with kinetic calculations, we study the ability of these compounds to enhance cluster formation and growth. The cluster structures are obtained and frequencies are calculated using three different DFT functionals (M06-2X, PW91, and ωB97X-D) with the 6-31++G(d,p) basis set. The electronic energies are corrected using an accurate DLPNO-CCSD(T)/def2-QZVPP level of theory. The evaporation rates are evaluated based on the calculated Gibbs free energies. The interaction between the ions and sulfuric acid or carboxylic acid group is strong, and thereby small two-component ionic clusters are found to be very stable against evaporation. The presence of bisulfate stimulates the cluster formation through addition of the sulfuric acid, whereas the presence of ammonium favors the addition of organic acids. Bisulfate and ammonium enhance the first steps of cluster formation; however, at atmospheric conditions further cluster growth is limited due to the weak interaction and fast evaporation of the larger three-component clusters. On the basis of our results it is therefore unlikely that the studied organic acids and sulfuric acid, even together with bisulfate, ammonia, or ammonium can drive new-particle formation via clustering mechanisms. Other mechanisms such as chemical reactions are needed to explain observed new-particle formation events in the presence of oxidized organic compounds resembling the acids studied here.

Rate enhancement in collisions of sulfuric acid molecules due to long-range intermolecular forces

“…3, exhibit a minimum at r = 4.1 Å, and the binding free energies are F = −0.29 and −0.27 eV for Loukonen et al (2010), and Ding et al (2003), respectively. This is in excellent agreement with the ab initio value of G = −0.30 eV obtained from Boltzmann-averaging over the four minimum energy dimer structures by Temelso et al (2012) at 298.15 K, and more recent calculations at a higher level of theory, which predict slightly weaker binding (−0.23 to −0.26 eV) (Elm et al, 2016;Myllys et al, 2017).…”

Piperazine Enhancing Sulfuric Acid-Based New Particle Formation: Implications for the Atmospheric Fate of Piperazine

“…81 The multi-step sampling scheme has extensively been applied to study atmospheric cluster formation. 70,78,[83][84][85][86][87][88] In brief, the scheme includes the following six steps: used to build initial configurations for the larger clusters starting over from (1). The initial PZ conformations for building the (PZ)1(SA)1 and (PZ)2 clusters were obtained from our previous AIMD simulation.…”

Closed-Shell Organic Compounds Might Form Dimers at the Surface of Molecular Clusters

“…19 Combined these theoretical studies suggest that other compounds or mechanisms are needed to explain experimentally measured formation events. 20 It has been shown both in field and smog chamber measurements that SOAs contain oligomeric macromolecules, which might be formed in either gas-or particle-phase reactions. [21][22][23][24][25][26] However, the reaction kinetics of covalently-bound dimer and higher order oligomer formation as well as the relative significance of participating vapours are unknown.…”