A simple method to derive the water activities of highly supersaturated binary electrolyte solutions from ternary solution data

Abstract

Abstract. Using mixing rules in electrolyte models for estimating the thermodynamic properties of multicomponent mixtures requires knowledge of data for each binary solution. Very often, a ternary solution in a single-particle levitation experiment can achieve a higher ionic strength as compared with the ionic strengths derived from any of the binary solutions alone. Using water activity data of ternary solutions and the Zdanovskii-Stokes-Robinson and the Kusik and Meissner (KM) equations, water activities of binary solutions of (NH4)2SO4, NaC1, and NH4C1 at supersaturations higher than any previously reported are calculated. With available data from the literature on aqueous supersaturated droplets of NH4NO3-(NH4)2SO 4 ternary solutions and letovicite at ambient temperatures, water activities (>0.32) of (NH4)2SO 4 solutions for ionic strengths up to 112 mol kg -• are obtained. The new water activity relation enables the use of the KM and Pitzer models at higher ionic strengths than in previous research. Applying the same method to the data on (NH4)2SO4-NaC1 and NH4NO3-NaC1 systems yields water activities In single-particle experiments using an electrodynamic balance, laboratory-generated ternary solution droplets can often attain a higher total ionic strength I or lower a w than any of the binary solutions alone before crystallization occurs. For example, Chan et al. [1992] found that an NH4NO3-(NH4)2SO 4 mixture can achieve a maximum attainable ionic strength (/max) and a minimum aw (aw,min) between the limits of the two binary solutions, as demonstrated in Table 1 In this paper, we present a method to calculate the water activities of binary supersaturated solutions from the data of ternary solutions using the ZSR and KM equations. The NH4NO3-(NH4)2SO 4 system is used as an example because its water activity data at different compositions are available and these data are comparable with estimations of the ZSR and KM equations [Chan et al., 1992]. The aim here is to obtain water activities of (NH4)2SO 4 solutions at lower values than any previously reported. Data from the acidic sulfate (H2SO 4-(NH4)2504) system, where applicable, are also included in the analysis. A similar approach is used for calculating the water activities of NaC1 and NH4C1 solutions using data from the literature and newly measured data of ternary solutions con- 30,193

Hygrometric determination of water activities, and osmotic and activity coefficients of NH4Cl–CaCl2–H2O at T=298.15 K

“…Bulk data are available in the literature, especially, by Robinson and Stokes [7] and Harned and Owen [8]. More recently, critical evaluation of the thermodynamic properties of aqueous calcium chloride have been reported by Rard and Clegg [9], and the water activities of ammonium chloride solutions have been determined using electrodynamic balance [10][11][12]. However, the experimental thermodynamic data for mixed ammonium and calcium chloride solutions are rather limited.…”

A new method for multicomponent activity coefficients of electrolytes in aqueous atmospheric aerosols

“…For self‐consistency, the binary electrolyte mole fractions, x E 0 , as a function of a w were also computed using the PSC model for all the electrolytes except for NH 4 Cl, Ca(NO 3 ) 2 , and CaCl 2 . The binary molality parameterization of Chan and Ha [1999] was used for NH 4 Cl as it is superior to the PSC predictions at high supersaturation (<50% RH), and the data given by Kim and Seinfeld [1995] were used for Ca(NO 3 ) 2 and CaCl 2 . The coefficients for x E 0 ( a w ) polynomial fits are listed in Table 3, and the binary molalities required for the ZSR equation are then computed as m E 0 = (55.509 x E 0 )/(1 − x E 0 ).…”

“… b Source: CW, Clegg et al [1998b] and Wexler and Clegg [2002]; KS, Kim and Seinfeld [1995]; CH, Chan and Ha [1999]. …”

Efflorescence Relative Humidity of Mixed Sodium Chloride and Sodium Sulfate Particles

“…For a droplet resulting from water uptake and salt dissolution, we can determine the salt molalities m α and m β by specifying the water activity and using the Zdanovskii−Stokes−Robinson (ZSR) relationship, where m i, 0 ( a w ) is the molality for the corresponding single-salt solution with the same water activity a w . Equation 4 has been commonly employed by many researchers. ,,, The correlations for m i, 0 ( a w ) are given in the Appendix. The total salt molality is hence m = m α + m β , and the water mass W w can becalculated from the molality and molecular weight of either salt.…”