Preprints
https://doi.org/10.5194/acp-2021-488
https://doi.org/10.5194/acp-2021-488

  17 Jun 2021

17 Jun 2021

Review status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Molecular scale description of interfacial mass transfer in phase separated aqueous secondary organic aerosol

Mária Lbadaoui-Darvas1, Satoshi Takahama1, and Athanasios Nenes1,2 Mária Lbadaoui-Darvas et al.
  • 1School of Architecture, Civil and Environmetal Engineering, Swiss Federal Institute of Technology, Lausanne, 1015, Switzerland
  • 2Institute of Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, Greece GR-26504

Abstract. Liquid-liquid phase separated (LLPS) aerosol particles are known to exhibit increased cloud condensation nuclei (CCN) activity compared to well mixed ones due to a complex effect of low surface tension and non-ideal mixing. The relation between the two contributions as well as the molecular scale mechanism of water uptake in the presence of an internal interface within the particle is to date not fully understood. Here we present steered molecular dynamics simulation studies of water uptake by a vapor/hydroxi-cis-pinonic acid/water double interfacial system at 200 K and 300 K. Simulated free energy profiles are used to map the water uptake mechanism and are decomposed into energetic and entropic contributions to highlight its main thermodynamic driving forces. Atmospheric implications are discussed in terms of gas/particle partitioning, intraparticle water redistribution timescales, and equilibrium saturation ratios of water vapor. Our simulations reveal a strongly temperature-dependent water uptake mechanism, whose most prominent features are determined by local extrema in conformational and orientational entropies near the organic/water interface which result in a reduced core uptake coefficient (ko/w = 0.05) and a concentration gradient of water in the organic shell at the higher temperature, while their effect is negligible at 200 K due to the explicit temperature dependence of entropic terms in the free energy profiles. The concentration gradient, which is a molecular level manifestation of non-ideal mixing – suspected to be a major factor to increase LLPS CCN activity – is responsible for maintaining LLPS and low surface tension even at very high relative humidities, thus reducing critical supersaturations. Thermodynamic driving forces are rationalised to be generalizable across different compositions. The conditions under which single uptake coefficients can be used to to describe growth kinetics as a function of temperature in LLPS particles are described.

Mária Lbadaoui-Darvas et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-488', Anonymous Referee #1, 01 Jul 2021
  • RC2: 'Comment on acp-2021-488', Anonymous Referee #2, 17 Jul 2021
  • AC1: 'Comment on acp-2021-488', Mária Lbadaoui-Darvas, 20 Sep 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-488', Anonymous Referee #1, 01 Jul 2021
  • RC2: 'Comment on acp-2021-488', Anonymous Referee #2, 17 Jul 2021
  • AC1: 'Comment on acp-2021-488', Mária Lbadaoui-Darvas, 20 Sep 2021

Mária Lbadaoui-Darvas et al.

Mária Lbadaoui-Darvas et al.

Viewed

Total article views: 468 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
321 136 11 468 6 7
  • HTML: 321
  • PDF: 136
  • XML: 11
  • Total: 468
  • BibTeX: 6
  • EndNote: 7
Views and downloads (calculated since 17 Jun 2021)
Cumulative views and downloads (calculated since 17 Jun 2021)

Viewed (geographical distribution)

Total article views: 461 (including HTML, PDF, and XML) Thereof 461 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 25 Oct 2021
Download
Short summary
Aerosol-cloud interactions constitute the most uncertain contribution to climate change. The uptake kinetics of water by aerosol is a central process of cloud droplet formation, yet its molecular scale mechanism is unknown. We use molecular simulations to study this process for phase-separated organic particles. Our results explain the increased cloud condensation activity of such particles and can be generalised over various compositions, thus may serve as a basis for future models.
Altmetrics