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Title: External and internal cloud condensation nuclei (CCN) mixtures: controlled laboratory studies of varying mixing states

Abstract. Changes in aerosol chemical mixtures modify cloud condensation nuclei (CCN)activity. Previous studies have developed CCN models and validated changesin external and internal mixing state with ambient field data. Here, wedevelop an experimental method to test and validate the CCN activation ofknown aerosol chemical composition with multicomponent mixtures and varyingmixing states. CCN activation curves consisting of one or more activationpoints are presented. Specifically, simplified two-component systems ofvarying hygroscopicity were generated under internal, external, andtransitional mixing conditions. κ-Köhler theory predictions werecalculated for different organic and inorganic mixtures and compared toexperimentally derived kappa values and respective mixing states. This workemploys novel experimental methods to provide information on the shifts inCCN activation data due to external to internal particle mixing fromcontrolled laboratory sources. Results show that activation curvesconsisting of single and double activation points are consistent withinternal and external mixtures, respectively. In addition, the height of theplateau at the activation points is reflective of the externally mixedconcentration in the mixture. The presence of a plateau indicates that CCNactivation curves consisting of multiple inflection points are externallymixed aerosols of varying water-uptake properties. The plateau disappearswhen mixing is promoted in the flow tube. At the end of the flow tubeexperiment, the aerosols are internally more » mixed and the CCN activated fractiondata can be fit with a single-sigmoid curve. The technique to mimicexternally to internally mixed aerosol is applied to non-hygroscopiccarbonaceous aerosol with organic and inorganic components. To ourknowledge, this work is the first to show controlled CCN activation of mixednon-hygroscopic soot with hygroscopic material as the aerosol populationtransitions from externally to internally mixed states in laboratoryconditions. Results confirm that CCN activation analysis methods used hereand in ambient data sets are robust and may be used to infer the mixingstate of complex aerosol compositions of unknown origin.

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Authors:
; ; ; ; ; ;
Award ID(s):
1744216
Publication Date:
NSF-PAR ID:
10108772
Journal Name:
Atmospheric Measurement Techniques
Volume:
12
Issue:
8
Page Range or eLocation-ID:
4277 to 4289
ISSN:
1867-8548
Sponsoring Org:
National Science Foundation
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