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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/acp-2018-831
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-831
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Sep 2018

Research article | 11 Sep 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

The effect of hydrophobic glassy organic material on the cloud condensation nuclei activity of internally mixed particles with different particle morphologies

Ankit Tandon1,2, Nicholas El Rothfuss1, and Markus D. Petters1 Ankit Tandon et al.
  • 1Department of Marine Earth and Atmospheric Sciences, North Carolina State University, Raleigh, 27695-8208, USA
  • 2School of Earth and Environmental Sciences, Central University of Himachal Pradesh, Dharamshala, 176215, India

Abstract. Particles composed of organic and inorganic components can assume core-shell morphologies. The kinetic limitation of water uptake due to the presence of a hydrophobic viscous outer shell may increase the critical supersaturation required to activate such particles into cloud droplets. Here we test this hypothesis through laboratory experiments. Results show that the viscosity of polyethylene particles is 5×106 Pa s at 60°C. Extrapolation of temperature dependent viscosity measurements suggests that the particles are glassy at room temperature. Cloud condensation nuclei (CCN) activity measurements demonstrate that pure polyethylene particles are CCN inactive at diameters less than 741nm and 2.5% water supersaturation. Thus, polyethylene is used as proxy for hydrophobic glassy organic material. Ammonium sulfate is used as proxy for hygroscopic CCN active inorganic material. Mixed particles were generated using coagulation of oppositely charged particles; charge-neutral polyethylene-ammonium sulfate dimers were then isolated for online observation. Morphology of these dimers was varied by heating, such that liquefied polyethylene partially or completely engulfed the ammonium sulfate. Critical supersaturation was measured as a function of dry particle volume, particle morphology, and organic volume fraction. The data show that kinetic limitations do not change the critical supersaturation of 50nm ammonium sulfate cores coated with polyethylene and polyethylene volume fractions up to 97%. Based on these results, and a synthesis of literature data, it is concluded that mass transfer limitations by glassy organic shells are unlikely to affect cloud droplet activation near laboratory temperatures.

Ankit Tandon et al.
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Short summary
Organic compounds may form a barrier to condensation. Such barriers have been hypothesized to prevent water and other substances from mixing with salt cores. This will hinder the particles' ability to aid cloud formation of sub-100 nm particles. Here we perform experiments encasing particles in plastic shells akin to water bottles. Against expectations, the plastic shell did not alter the droplet activation behavior of the encased particles. Water appears to readily permeate the plastic shell.
Organic compounds may form a barrier to condensation. Such barriers have been hypothesized to...
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