Abstract
Abstract. Changes in aerosol chemical mixtures modify cloud condensation nuclei (CCN) activity. Previous studies have developed CCN models and validated changes in external and internal mixing state with ambient field data. Here, we develop an experimental method to test and validate the CCN activation of known aerosol chemical composition with multicomponent mixtures and varying mixing states. CCN activation curves consisting of one or more activation points are presented. Specifically, simplified two-component systems of varying hygroscopicity were generated under internal, external, and transitional mixing conditions. κ-Köhler theory predictions were calculated for different organic and inorganic mixtures and compared to experimentally derived kappa values and respective mixing states. This work employs novel experimental methods to provide information on the shifts in CCN activation data due to external to internal particle mixing from controlled laboratory sources. Results show that activation curves consisting of single and double activation points are consistent with internal and external mixtures, respectively. In addition, the height of the plateau at the activation points is reflective of the externally mixed concentration in the mixture. The presence of a plateau indicates that CCN activation curves consisting of multiple inflection points are externally mixed aerosols of varying water-uptake properties. The plateau disappears when mixing is promoted in the flow tube. At the end of the flow tube experiment, the aerosols are internally mixed and the CCN activated fraction data can be fit with a single-sigmoid curve. The technique to mimic externally to internally mixed aerosol is applied to non-hygroscopic carbonaceous aerosol with organic and inorganic components. To our knowledge, this work is the first to show controlled CCN activation of mixed non-hygroscopic soot with hygroscopic material as the aerosol population transitions from externally to internally mixed states in laboratory conditions. Results confirm that CCN activation analysis methods used here and in ambient data sets are robust and may be used to infer the mixing state of complex aerosol compositions of unknown origin.
Highlights
Atmospheric cloud condensation nuclei (CCN) are comprised of complex mixtures of organic and inorganic compounds
The shifting of the CCN activation sigmoid is expected of internally mixed particles formed via the coagulation of separate particle distributions (Farmer et al, 2015)
Results confirm that the experimental CCN activation curves of aerosol provide insight into the type of mixing and the various levels of hygroscopicities that are chemically representative
Summary
Atmospheric cloud condensation nuclei (CCN) are comprised of complex mixtures of organic and inorganic compounds. D. Vu et al.: External and internal cloud condensation nuclei mixtures the mixing state and the chemical composition can greatly improve CCN predictions and has been the focus of several studies (e.g., but not limited to Bilde and Svenningsson, 2004; Abbatt et al, 2005; Henning et al, 2005; Svenningsson et al, 2006; King et al, 2007; Cubison et al, 2008; Kuwata and Kondo, 2008; Zaveri et al, 2010; Su et al, 2010; Wang et al, 2010; Spracklen et al, 2011; Ervens et al, 2010; AsaAwuku et al, 2011; Lance et al, 2013; Liu et al, 2013; Jurányi et al, 2013; Paramonov et al, 2013; Padró et al, 2012; Moore et al, 2012; Meng et al, 2014; Bhattu and Tripathi, 2015; Almeida et al, 2014; Schill et al, 2015; Crosbie et al, 2015; Che et al, 2016; Ching et al, 2016; Mallet et al, 2017; Sánchez Gácita et al, 2017; Cai et al, 2018; Schmale et al, 2018; Mahish et al, 2018; Kim et al, 2018; Chen et al, 2019; Stevens and Dastoor, 2019)
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