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

Abstract

Abstract. Collisions of molecules and clusters play a key role in determining the rate of atmospheric new particle formation and growth. Traditionally the statistics of these collisions are taken from kinetic gas theory assuming spherical noninteracting particles, which may significantly underestimate the collision coefficients for most atmospherically relevant molecules. Such systematic errors in predicted new particle formation rates will also affect large-scale climate models. We studied the statistics of collisions of sulfuric acid molecules in a vacuum using atomistic molecular dynamics simulations. We found that the effective collision cross section of the H2SO4 molecule, as described by an optimized potentials for liquid simulation (OPLS). OPLS all-atom force field, is significantly larger than the hard-sphere diameter assigned to the molecule based on the liquid density of sulfuric acid. As a consequence, the actual collision coefficient is enhanced by a factor of 2.2 at 300 K compared with kinetic gas theory. This enhancement factor obtained from atomistic simulation is consistent with the discrepancy observed between experimental formation rates of clusters containing sulfuric acid and calculated formation rates using hard-sphere kinetics. We find reasonable agreement with an enhancement factor calculated from the Langevin model of capture, based on the attractive part of the atomistic intermolecular potential of mean force.

Supplementary material to "Sulfuric acid-amine nucleation in urban Beijing"

“…for CS (Chan and Mozurkewich, 2001;Kürten et al, 2018;Stolzenburg et al, 2019). The correction factor of 2.3 agrees with the results obtained by atomistic simulation (Halonen et al, 2019).…”

Heterogeneous Nucleation of Butanol on NaCl: A Computational Study of Temperature, Humidity, Seed Charge, and Seed Size Effects

“…Together with the seed restructuring, the presence of water may also increase the total polarity of cluster, which could further enhance the collision rate through dipole–dipole or ion–dipole interactions. 74 However, this potential effect is not modeled in this study. It is also known that larger NaCl seeds may “shrink” due to dissolution in the presence of water 75 and n -propanol.…”

Homogeneous nucleation of carbon dioxide in supersonic nozzles II: molecular dynamics simulations and properties of nucleating clusters

“…While neglecting long-range interactions between molecules systematically underestimates the collision rates, [28][29][30][31] the enhancement factor for weakly interacting neutral molecules, such as CO 2 , is likely to be rather small. In equilibrium with bulk liquid (i.e.…”