Efflorescence Relative Humidity of Mixed Sodium Chloride and Sodium Sulfate Particles

Abstract

We study the efflorescence relative humidity (ERH) of particles composed of sodium chloride and sodium sulfate. Both experimental and theoretical investigations are conducted to explore the effects of particle size and mixing ratios between two inorganic materials on ERH. A previously developed theoretical model (Gao et al. J. Phys. Chem. A 2006, 110, 7602; ref 1) is applied as the framework to build a formulation assuming that one salt nucleates much faster than the other, and the critical nuclei formation of the former controls the rate of efflorescence. The predicted ERHs agree favorably with the experimental data, except for particles containing Na2SO4 in a mole fraction of around 0.25. At this composition, our model underestimates the ERH, indicating certain factors involved in the efflorescent processes that are overlooked in our formulation. Relative to particles larger than 40 nm, the Kelvin effect more significantly affects particles smaller than this size.

Efficient bulk mass accommodation and dissociation of N<sub>2</sub>O<sub>5</sub> in neutral aqueous aerosol

“…In the absence of aerosol-phase nitrate, γ * for Na 2 SO 4 at 70 % RH is comparable to that reported by Mentel et al (1999). At 50 % RH, it is likely that the Na 2 SO 4 particles remained effloresced (Gao et al, 2007) (the lowest RH in the aerosol conditioning system was 40 %), explaining the low γ of 0.0053, which is comparable to that previously reported for dry ammonium sulfate (Hallquist et al, 2003).…”

Forward flux sampling calculation of homogeneous nucleation rates from aqueous NaCl solutions

“…23. The SPC/E and JC force fields underestimate the nucleation rate by around 10 orders of magnitude compared to the experimental data from Gao et al 47 and Na et al 46 Large discrepancies between simulation-based nucleation rates and experimental data have been observed for many nucleation processes, from crystallization of hard spheres 35 to ice nucleation. 28 The nucleation rate is sensitive to several thermodynamic quantities, especially the crystal/solution interfacial tension.…”

“…Lanaro and Patey 20 also conducted large scale MD simulation with the SPC/E and JC force fields at similar supersaturation, and based on their reported induction time, their nucleation rate is consistent with the present result. There are few experimental studies of homogeneous nucleation of NaCl crystals from solution, 18,46,47 and Zimmermann et al 23 summarized these experimental estimates of nucleation rates in the Supplementary Information of Ref. 23.…”

Crystal nucleation initiated by transient ion-surface interactions at aerosol interfaces

“…It is unclear whether a purely hydrophobic aerosol (that is, without charged functional groups) would induce efflorescence via a collision. Furthermore, any potential aqueous-phase size and temperature dependence on contact efflorescence remains to be explored further, although the efflorescence RH of aqueous aerosols remains markedly similar across a wide range of diameters ( 29 ) and temperatures ( 36 ). Also, we note that crystal nucleation and ionic surface propensity have been intensely debated subjects for the past century, and their respective mechanisms remain controversial ( 13 , 20 ).…”