Preprints
https://doi.org/10.5194/acp-2021-561
https://doi.org/10.5194/acp-2021-561

  26 Jul 2021

26 Jul 2021

Review status: this preprint is currently under review for the journal ACP.

Droplet activation of moderately surface active organic aerosol predicted with six approaches to surface activity

Sampo Vepsäläinen1, Silvia M. Calderón1,2, Jussi Malila1, and Nønne L. Prisle1,3 Sampo Vepsäläinen et al.
  • 1Nano and Molecular Systems Research Unit, University of Oulu, P.O. Box 3000, FI-90014, Oulu, Finland
  • 2Finnish Meteorological Institute, P.O. Box 1627, FI-70211, Kuopio, Finland
  • 3Center for Atmospheric Research, University of Oulu, P.O. Box 4500, FI-90014, Oulu, Finland

Abstract. Surface active compounds (surfactants) found in atmospheric aerosols can decrease droplet surface tension as they adsorb to the droplet surfaces simultaneously depleting the droplet bulk. These processes may influence the activation properties of aerosols into cloud droplets and investigation of their role in cloud microphysics has been ongoing for decades. In this study, we have used six different approaches documented in the literature to represent surface activity in Köhler calculations predicting cloud droplet activation properties for particles consisting of one of three different moderately surface active organics mixed with ammonium sulphate in different ratios. We find that the different models predict comparable activation properties at small organic mass fractions in the dry particles for all three moderately surface active organics tested, even with large differences in the predicted degree of bulk-to-surface partitioning of the surface active component. However, differences between the models regarding both the predicted critical diameter and supersaturation for the same dry particle size increase with the organic fraction in the particles. Comparison with available experimental data shows that assuming complete bulk-to-surface partitioning of the organic component (total depletion of the bulk) along the full droplet growth curve does not adequately represent the activation properties of particles with high moderate surfactant mass fractions. Accounting for the surface tension depression mitigates some of the effect. Models that include the possibility for partial bulk-to-surface partitioning yield comparable results to the experimental data, even at high organic mass fractions in the particles. The study highlights the need for using thermodynamically consistent model frameworks to treat surface activity of atmospheric aerosols and for firm experimental validation of model predictions across a wide range of states relevant to the atmosphere.

Sampo Vepsäläinen 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-2021-561', Anonymous Referee #1, 20 Aug 2021
  • RC2: 'Comment on acp-2021-561', Anonymous Referee #2, 27 Aug 2021

Sampo Vepsäläinen et al.

Sampo Vepsäläinen et al.

Viewed

Total article views: 370 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
290 71 9 370 27 3 4
  • HTML: 290
  • PDF: 71
  • XML: 9
  • Total: 370
  • Supplement: 27
  • BibTeX: 3
  • EndNote: 4
Views and downloads (calculated since 26 Jul 2021)
Cumulative views and downloads (calculated since 26 Jul 2021)

Viewed (geographical distribution)

Total article views: 361 (including HTML, PDF, and XML) Thereof 361 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 23 Sep 2021
Download
Short summary
Atmospheric aerosols act as seeds for cloud formation. Many aerosols contain surface active material which accumulates in the surface of growing droplets. This can affect cloud droplet activation, but the broad significance of the effect and the best way to model it is still debated. We compare predictions of six different model approaches to surface activity of organic aerosols and find significant differences between the models, especially with large fractions of organic in the dry particles.
Altmetrics