04 Feb 2021
04 Feb 2021
Status: this preprint is currently under review for the journal ACP.

Energetic analysis of succinic acid in water droplets: insight into the size-dependent solubility of atmospheric nanoparticles

Chuchu Chen1,2, Xiaoxiang Wang1,6, Kurt Binder3, Mohammad Mehdi Ghahremanpour4,5, David van der Spoel4, Ulrich Pöschl2, Hang Su2, and Yafang Cheng1 Chuchu Chen et al.
  • 1Minerva Research Group, Max Planck Institute for Chemistry, Hahn-Meitner-Weg 5, 55128 Mainz, Germany
  • 2Multiphase Chemistry Department, Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany
  • 3Institute of Physics, Johannes Gutenberg University of Mainz, Staudinger Weg 7, 55128 Mainz, Germany
  • 4Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, Box 596, SE-75124 Uppsala, Sweden
  • 5Department of Chemistry, Yale University, New Haven, CT 06520-8107, USA
  • 6School of Environmental Science and Engineering, Southern University of Science and Technology, 518055 Shenzhen, P. R. China

Abstract. Size-dependent solubility is prevalent in atmospheric nanoparticles, but a molecular level understanding is still insufficient, especially for organic compounds. Here, we performed molecular dynamics simulations to investigate the size dependence of succinic acid solvation on the scale of ~1–4 nm with the potential of mean forces method. Our analyses reveal that the surface preference of succinic acid is stronger for a droplet than the slab of the same size, and the surface propensity is enhanced due to the curvature effect as the droplet becomes smaller. Energetic analyses show that such surface preference is primarily an enthalpic effect in both systems, while the entropic effect further enhances the surface propensity in droplets. On the other hand, with decreasing droplet size, the solubility of succinic acid in the internal bulk volume may decrease, imposing an opposite effect on the size dependence of solubility as compared with the enhanced surface propensity. Meanwhile, structural analyses, however, show that the surface to internal bulk volume ratio increases drastically, especially when considering the surface in respect to succinic acid, e.g., for droplet with radius of 1 nm, the internal bulk volume would be already close to zero for the succinic acid molecule.

Chuchu Chen et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2020-1329', Anonymous Referee #1, 16 Mar 2021
  • RC2: 'Comment on acp-2020-1329', Anonymous Referee #2, 24 May 2021
  • RC3: 'Comment on acp-2020-1329', Anonymous Referee #3, 31 May 2021

Chuchu Chen et al.

Chuchu Chen et al.


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Short summary
Size dependence of succinic acid solvation in the nanoparticles is investigated based on the molecular dynamics (MD) simulation and energetic analysis. The results show a stronger surface preference and a weaker internal bulk volume solvation of succinic acid in the smaller droplets, which may explain the previously observed size-dependent phase-state of aerosol nanoparticles containing organic molecules, fundamentally promoting a better understanding of atmospheric aerosols.