The Effects of Organic Species on the Hygroscopic Behaviors of Inorganic Aerosols

Abstract

Water-soluble organic compounds have recently received much attention because of their ability to absorb water and alter the hygroscopic properties of inorganic aerosols. The effects of glycerol, succinic acid, malonic acid, citric acid, and glutaric acid on the water cycles (water activities during particle evaporation and growth), crystallization relative humidities (CRH), and deliquescence relative humidities (DRH) of sodium chloride (NaCl) and ammonium sulfate (AS) were studied using an electrodynamic balance (EDB). The growth factors of these inorganic and organic mixtures were lower than those of the pure inorganic species. The presence of all these organics in the mixed particle reduce the water absorption of NaCl but enhance that of AS relative to that of the pure inorganic salts. Glycerol and succinic acid did not affect the deliquescence properties of NaCl and AS, although succinic acid increased the CRH of NaCl and AS. Malonic acid and citric acid, behaving as nondeliquescent species in single particle studies, caused NaCl and AS particles to absorb a significant amount of water before deliquescence. Glutaric acid caused NaCl and AS to deliquesce gradually, spanning a wide range of relative humidity. The ZSR model was found to be useful in predicting the water activity of the mixtures and the growth ratios. However, the detailed crystallization and deliquescence behaviors of the organic/inorganic mixtures cannot be easily predicted from the hygroscopic properties of the individual components.

Hygroscopic Growth and Deliquescence of NaCl Nanoparticles Coated with Surfactant AOT

“…12,32 Measured GF values for the mixed particles were approximately consistent with the assumption that the organic and inorganic species adsorb water independently, in accordance with the ZdanovskiiStokes-Robinson (ZSR) model. 33,34 Similar conclusions were reached in studies of water activities above the bulk mixtures of the same compounds. 35,36 The main objective of this work is to test the effect of sparingly soluble organic coatings on hygroscopic properties of NaCl nanoparticles.…”

Water Content and Phase Transitions in Particles of Inorganic and Organic Species and their Mixtures Using Micro-Raman Spectroscopy

“…Variation in the water content of the AS-MA particles in the course of a humidity cycle is shown in Figure 3 along with data from previous measurements using the EDB techniques (Choi and Chan 2002;Ling and Chan 2008). The AS-MA particles in this study are of the same composition (1:1 mole ratio) with those studied in the literature.…”

Roles of the Phase State and Water Content in Ozonolysis of Internal Mixtures of Maleic Acid and Ammonium Sulfate Particles

“…In this work, the particle deliquesced completely at 74-75% RH when the normalized FWHM of the AS peak surged, consistent with the predictions. The full DRH of the 30 wt% MA particle was lower than the respective pure AS (80% RH) and MA (86% RH) values (Peng et al 2001;Choi and Chan 2002), owing to the entropy enhancement during solvation/mixing (Marcolli et al 2004). The DRH reduction of mixed particles has been reported earlier even for sparingly soluble organic/inorganic mixtures, such as the mixture of adipic acid and AS (Yeung et al 2009).…”

“…Some highly aged organic aerosols may have oxygen-to-carbon ratio as high as unity (Aiken et al 2008). The oxidative transformation results in changing aerosol loadings and physicochemical properties, such as the hygroscopicity (Choi and Chan 2002;Yeung et al 2009), the cloud condensation nuclei (CCN) activity (Shilling et al 2007), and the optical properties (Shapiro et al 2009), which in turn complicate the highly uncertain radiative forcing of aerosols (Heald et al 2005). It is important to understand how these heterogeneous aging processes affect the transformation of organic aerosols.…”