Phase Transformation and Growth of Hygroscopic Aerosols

Abstract

DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document. AbstractAmbient aerosols frequently contain large portions of hygroscopic inorganic salts such as chlorides, nitrates, and sulfates in either pure or mixed forms. Such inorganic salt aerosols exhibit the properties of deliquescence and efflorescence in air. The phase transformation from a solid particle to a saline droplet usually occurs spontaneously when the relative humidity of the atmosphere reaches a level specific to the chemical composition of the aerosol particle. Conversely, when the relative humidity decreases and becomes low enough, the saline droplet will evaporate and suddenly crystallize, expelling all its water content. The phase transformation and growth of aerosols play an important role in many atmospheric processes affecting air quality, visibility degradation, and climate changes. In this chapter, an exposition of the underlying thermodynamic principles is given, and recent advances in experimental methods utilizing singleparticle levitation are discussed. In addition, pertinent and available thermodynamic data, which are needed for predicting the deliquescence properties of single and multi-component aerosols, are compiled. This chapter is useful to research scientists who are either interested in pursuing further studies of aerosol thermodynamics, or required to model the dynamic behavior of hygroscopic aerosols in a humid environment.

Evaporation and dispersion of respiratory droplets from coughing

“…The droplet nuclei size of a droplet of NaCl solution or of KCl solution as a function of RH was used to validate the equilibrium size by comparing it to the experimental data from Tang (), as shown in Figure a. The mass fractions of NaCl and KCl solutes were 7.7% and 10%, respectively, under equilibrium at a RH = 95%; no insoluble solids were contained in the droplets.…”

“…The sodium chloride and potassium chloride dissolved in respiratory droplets have very strong hygroscopicity, and they tend to absorb vapor from the ambient air. In humid air, the droplets are composed of an aqueous solution instead of desiccated particles (Tang, ). Pruppacher and Klett () investigated and reviewed the effects of insoluble solids suspended in liquid droplets in equilibrium.…”

Chemical analysis of acoustically levitated drops by Raman spectroscopy

“…In contrast to the case for electrodynamically levitated microdrops of Na 2 SO 4 (aq) [27], where physical measurements of size, pressure, and temperature were used, the crystallization of an acoustically levitated drop of saturated aqueous solution of Na 2 SO 4 at ambient room conditions proceeded—in the case of the results presented in Fig. 9—via an intermediate state of Na 2 SO 4 ·10H 2 O towards anhydrous Na 2 SO 4 .…”

Further Laboratory Experiments on Aerosol Scavenging in Mixed Clouds to Assess the Role of Phoretic Forces and Particle Solubility

“…Hydration properties of hygroscopic aerosol particles cannot be predicted from the bulk solution properties [13]. Upon evaporation the solution droplets become highly supersaturated until crystallization occurs at about 58%RH to anhydrous particles.…”

“…and summarizing chapter by [13] devoted to the deliquescence and growth of mixed salt particles relating aerosol phase transformation to the solubility diagrams for multi-component electrolyte solutions. From the growth and evaporation cycles at 25˚C NaCl particles deliquesce at 75.5% RH and crystallizes again at 48% RH.…”