Cloud condensation nucleus activity comparison of dry- and wet-generated mineral dust aerosol: the significance of soluble material

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 FrenkelHalsey-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.

A comprehensive laboratory study on the immersion freezing behavior of illite NX particles: a comparison of 17 ice nucleation measurement techniques

“…Again, this would change the surface charge distribution and potentially affect the ice-nucleating efficiency of illite particles. If wet particle generation (dispersion of aqueous suspension by means of a pressurized air atomizer) is used, the redistribution of cations between suspended particles may be an issue, as suggested by Garimella et al (2014) for the case of CCN experiments. Further studies of samples without modification or ageing after dry dispersion or wet suspension are needed to get a better idea of the method intercomparison.…”

“…More quantitative investigations of the acid processing of both reference and atmospherically relevant materials, and of acid processing's influence on their respective immersion mode ice nucleation efficiencies, are needed. Recently, re-partitioning of soluble components of both swelling and non-swelling clay minerals and their effect on cloud condensation nucleation activity was reported (Sullivan et al, 2010;Kumar et al, 2011;Garimella et al, 2014). To address a potential importance of this effect on the icenucleating activity of illite NX in the wet dispersion experiments, we have measured the concentration of cations released by the illite NX sample placed into deionized water as a function of time, as described in Sect.…”

Deposition and immersion-mode nucleation of ice by three distinct samples of volcanic ash

“…Additionally, a new parameterization has also been shown that assumes surface area of the volcanic to be 10 times greater than the original parameterization to account for the high porosity of volcanic ash (dashed line). has been shown that wet generation techniques can affect the hygroscopicity and cloud droplet formation ability of mineral dust (Sullivan et al, 2010;Garimella et al, 2014). Thus, allowing the ash samples to shake in solution for at least 12 h prior to immersion freezing experiments could cause the dissolution/redistribution of active surface sites.…”

Properties of cloud condensation nuclei (CCN) in the trade wind marine boundary layer of the western North Atlantic

“…Jung et al (2013) reported a hygroscopicity parameter, κ, value of 0.02-0.03 for the accumulation mode particles at different altitudes including the MBL, east of Barbados during a pronounced mineral dust episode. Such low κ values close to 0.01 as for pure dust (Garimella et al, 2014;Petters and Kreidenweis, 2007) are indicative of an accumulation mode dominated by dust with only minor amounts of hygroscopic particulate matter (PM) present. Hence, mineral dust particles may play an important role as CCN under certain conditions over the North Atlantic.…”