External and internal cloud condensation nuclei (CCN) mixtures: controlled laboratory studies of varying mixing states
<p>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 activati...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-08-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/12/4277/2019/amt-12-4277-2019.pdf |
| Summary: | <p>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. <span class="inline-formula"><i>κ</i></span>-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.</p> |
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| ISSN: | 1867-1381 1867-8548 |