Abstract
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.
Highlights
It is well established that organic compoundsare ubiquitous in marine aerosol; they can interact with water and affect aerosol hygroscopicity, droplet surface tension, and Cloud Condensation Nuclei (CCN) activity [1,2,3,4,5,6]
The surface tension depression results are similar to results from dissolved organic marine matter [34]
CCN activity, chemical composition and droplet growth measurements coupled with Köhler Theory
Summary
It is well established that organic compounds (especially water-soluble organic compounds, WSOC). Are ubiquitous in marine aerosol; they can interact with water and affect aerosol hygroscopicity, droplet surface tension, and Cloud Condensation Nuclei (CCN) activity [1,2,3,4,5,6]. Given the complexity of the water-soluble organic fraction, characterization is done by measuring the size-resolved CCN activity of the material, surface tension depression and using Köhler Theory Analysis (KTA) [33,34,35]. To infer the thermodynamic properties (average molar volume, surfactant tension depression) of the organic fraction and its potential impact on droplet growth rate kinetics. These properties are related to the influence of primary emissions and in-cloud oxidation processes on the CCN activity of the organic compounds
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