Role of Base Strength, Cluster Structure and Charge in Sulfuric Acid-Driven Particle Formation

Abstract

<p><strong>Abstract.</strong> In atmospheric sulfuric acid-driven particle formation, bases are able to stabilize the initial molecular clusters, and thus enhance particle formation. The enhancing potential of a stabilizing base is affected by different factors, such as the basicity and abundance. Here we use weak (ammonia), medium strong (dimethylamine) and very strong (guanidine) bases as representative atmospheric base compounds, and systematically investigate their ability to stabilize sulfuric acid clusters. Using quantum chemistry, we study proton transfer as well as intermolecular interactions and symmetry in clusters, of which the former is directly related to the base strength and the latter to the structural effects. Based on the theoretical cluster stabilities and cluster population kinetics modeling, we provide molecular-level mechanisms of cluster growth and show that in electrically neutral particle formation, guanidine can dominate formation events even at relatively low concentrations. However, when ions are involved, charge effects can stabilize small clusters also for weaker bases. In this case the atmospheric abundance of the bases becomes more important, and thus ammonia is likely to play a key role. The theoretical findings are validated by cluster distribution experiments, as well as comparisons to previously reported particle formation rates, showing a good agreement.</p>

A study on the fragmentation of sulfuric acid and dimethylamine clusters inside an Atmospheric Pressure interface Time Of Flight Mass Spectrometer

“…The smallest detected 1:1 ratio cluster is 2D2S1b, we do not observe 1D1S1B cluster probably due to its lower stability compared to a larger cluster. This is in agreement with the computed trend of stability of negatively charged sulfuric acid-dimethylamine clusters (Myllys et al, 2019). Moreover, our detected clusters are similar to those detected in a previous study of the same sulfuric acid and dimethylamine solution (Thomas et al, 2016).…”

Supplementary material to "A study on the fragmentation of sulfuric acid and dimethylamine clusters inside an Atmospheric Pressure interface Time Of Flight Mass Spectrometer"

“…We used quantum chemistry data taken from (Myllys et al, 2019). These data are the global free-energy-minimum structures of our studied clusters, with the geometry optimization and vibrational frequency analysis were carried out at the ωB97X-D/ B97X-D/ 6-31++G(d,p) level of theory.…”

“…These data are the global free-energy-minimum structures of our studied clusters, with the geometry optimization and vibrational frequency analysis were carried out at the ωB97X-D/ B97X-D/ 6-31++G(d,p) level of theory. Additionally, to obtain accurate binding energies, the electronic energies were corrected at the 90 95 DLPNO-CCSD(T) method with the aug-cc-pVTZ basis set (more details on the technical aspects of the quantum chemistry calculations can be found in (Myllys et al, 2019).…”

Hydration of Atmospheric Molecular Clusters III: Procedure for Efficient Free Energy Surface Exploration of Large Hydrated Clusters

“…5 In the lower atmosphere other stabilizing vapour molecules, such as atmospheric bases 6 and highly oxidized organic compounds, 7 are required to facilitate the particle formation process. In particular trace species with high basicities such monoamines, 8-14 diamines [15][16][17] or guanidine [18][19][20] are potent candidates to stabilize sulfuric acid clusters and enhance new particle formation in the lower troposphere.…”