Abstract
Abstract. This study examines the interaction of clay mineral particles and water vapor for determining the conditions required for cloud droplet formation. Droplet formation conditions are investigated for two common clay minerals, illite and sodium-rich montmorillonite, and an industrially derived sample, Arizona Test Dust. Using wet and dry particle generation coupled to a differential mobility analyzer (DMA) and cloud condensation nuclei counter, the critical activation of the clay mineral particles as cloud condensation nuclei is characterized. Electron microscopy (EM) is used in order to determine non-sphericity in particle shape. It is also used in order to determine particle surface area and account for transmission of multiply charged particles by the DMA. Single particle mass spectrometry and ion chromatography are used to investigate soluble material in wet-generated samples and demonstrate that wet and dry generation yield compositionally different particles. Activation results are analyzed in the context of both κ-Köhler theory (κ-KT) and Frenkel–Halsey–Hill (FHH) adsorption activation theory. This study has two main results: (1) κ-KT is the suitable framework to describe clay mineral nucleation activity. Apparent differences in κ with respect to size arise from an artifact introduced by improper size-selection methodology. For dust particles with mobility sizes larger than ~300 nm, i.e., ones that are within an atmospherically relevant size range, both κ-KT and FHH theory yield similar critical supersaturations. However, the former requires a single hygroscopicity parameter instead of the two adjustable parameters required by the latter. For dry-generated particles, the size dependence of κ is likely an artifact of the shape of the size distribution: there is a sharp drop-off in particle concentration at ~300 nm, and a large fraction of particles classified with a mobility diameter less than ~300 nm are actually multiply charged, resulting in a much lower critical supersaturation for droplet activation than expected. For wet-generated particles, deviation from κ-KT is likely a result of the dissolution and redistribution of soluble material. (2) Wet generation is found to be unsuitable for simulating the lofting of fresh dry dust because it changes the size-dependent critical supersaturations by fractionating and re-partitioning soluble material.
Highlights
Atmospheric aerosols play a significant role in the earth’s climate system, especially in the radiative budget and the hydrological cycle
This study considers the effect of the generation method on activation potential using electron microscopy (EM), ion chromatography (IC), and Particle Analysis by Laser Mass Spectrometry (PALMS), comparing the results for dry- and wet-generated aerosol
The size distribution of the dry-generated cycloneimpacted particles resembles that of the dry-generated particles, but the overall concentration of particles is lower and the peak concentration is shifted to a smaller size
Summary
Atmospheric aerosols play a significant role in the earth’s climate system, especially in the radiative budget and the hydrological cycle. Their influence on climate is via the socalled direct and indirect radiative forcing effects (Denman and Brasseur, 2007). The direct effect of aerosols on atmospheric radiation is through the scattering and absorption of light in both the shortwave and long-wave regimes (Seinfeld and Pandis, 2006; Yu et al, 2006; Christopher et al, 2009).
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.