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Published November 2015 | Published
Journal Article Open

CCN Properties of Organic Aerosol Collected Below and within Marine Stratocumulus Clouds near Monterey, California


The composition of aerosol from cloud droplets differs from that below cloud. Its implications for the Cloud Condensation Nuclei (CCN) activity are the focus of this study. Water-soluble organic matter from below cloud, and cloud droplet residuals off the coast of Monterey, California were collected; offline chemical composition, CCN activity and surface tension measurements coupled with Köhler Theory Analysis are used to infer the molar volume and surfactant characteristics of organics in both samples. Based on the surface tension depression of the samples, it is unlikely that the aerosol contains strong surfactants. The activation kinetics for all samples examined are consistent with rapid (NH4)2SO4 calibration aerosol. This is consistent with our current understanding of droplet kinetics for ambient CCN. However, the carbonaceous material in cloud drop residuals is far more hygroscopic than in sub-cloud aerosol, suggestive of the impact of cloud chemistry on the hygroscopic properties of organic matter.

Additional Information

© 2015 by the authors; licensee MDPI, Basel, Switzerland. This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Received: 31 August 2015 / Revised: 5 October 2015 / Accepted: 10 October 2015 / Published: 28 October 2015. (This article belongs to the Special Issue Atmospheric Composition Observations) The work in this study was supported by an NSF CAREER Award. In addition, we would like to thank Dr. Rodney Weber and his students at the Georgia Institute of Technology for the use of the Total Organic Carbon (TOC) Turbo Siever Analyzer and Dr. Christos Fountoukis for his help in running the ISORROPIA II code. Author Contributions: Akua Asa-Awuku is co-corresponding author and conducted laboratory experiments, collected and analyzed data sets, and played a significant role in the writing of the manuscript. Armin Sorooshian collected samples in the field, aided in analysis and writing. Richard C. Flagan and John H. Seinfeld devised flight experiments. Athanasios Nenes is co-corresponding author and conceived and devised experiments, analysis, and significantly contributed to writing. The authors declare no conflict of interest.

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October 25, 2023