Thermodynamic and optical properties of mixed‐salt aerosols of atmospheric importance

Abstract

Abstract. Extensive water activity, density, and refractive index data at 25øC are reported for mixed-salt solutions, NaC1-KCI, NaC1-NaNO 3, NaCI-Na2SO 4, Na2SO4-NaNO 3, and (NH4)2SO 4-Na2SO 4. The data are obtained from hydration experiments using the single-particle levitation technique developed recently for measuring the thermodynamic and optical properties of microdroplets. These data, coveting the whole concentration range from dilute solutions to high supersaturations, provide an opportunity to explore the light-scattering properties of both internal and external mixtures of the chloride, sulfate, and nitrate aerosols of atmospheric importance. It is shown that for sulfate and nitrate aerosols as solution droplets, the light-scattering properties do not differ appreciably among all mixture types and compositions, as long as the dry-salt aerosols have the same particle-size distribution. However, for mixed-salt aerosols containing NaC1, the light-scattering properties do depend upon the composition and particle-size distribution, although not so much on the mixture type.

General circulation model assessment of direct radiative forcing by the sulfate‐nitrate‐ammonium‐water inorganic aerosol system

“…Mie scattering calculations require knowledge of the aerosol refractive index to compute single-particle scattering and absorption cross sections for any given particle size. We use the method of partial molar refraction [Stelson, 1990] to compute the refractive index of the aerosol mixture present in a given GCM grid cell at a given time step based on laboratory measurements of single-component aerosol optical properties [Tang and Munkelwitz, 1994;Tang, 1996Tang, , 1997. Given that this model, like other global aerosol models, does not resolve the aerosol size distribution, one must be assumed for purposes of calculating aerosol optical properties.…”

Measuring Mass-Based Hygroscopicity of Atmospheric Particles through in Situ Imaging

“…Dehydration data points are shown as green filled triangles. Deliquescence relative humidities (DRH) for NaCl and ammonium sulfate were obtained from Tang 47 and NaBr and KCl are from Cohen et al 41 The error bars show the standard error of each point with sample sizes between two and six. Table presenting hygroscopicity, mass-based growth factor at 80% RH (g m ), hygroscopicity parameter κ equiv at 80% RH, inorganic atomic composition, STXM images at 4% and 90% RH acquired at 525 eV, and mixing state classification for 15 atmospheric particles.…”

Real refractive index: Dependence on relative humidity and solute composition with relevancy to atmospheric aerosol particles

“…Firstly, the ZSR and PMR models have been combined for the first time to represent n as a function of RH for aerosol droplets, especially for organiccontaining aerosols (Previous research completed by Munkelwitz [1991, 1994] and Tang et al [1997] presented measured n values as a function of molality (equivalent to mfs) and molality as a function of a w without explicitly showing the linkage between n and a w for select solution droplets containing inorganic salts.) despite the application and success of these two models in aerosol research [e.g., Weast et al, 1986;Tang, 1997]. Secondly, this research provides for the first time the evaluation of closure between experimental measurements and model calculations with respect to the direct dependence of n on RH for the aqueous solutions containing inorganic, organic and mixtures of inorganic and organic solutes.…”

“…As will be discussed later, the red line marked ''n predicted by equation (2)'' was plotted by fitting the values of n and mfs to a straight line (equation (2)). Tang [1997], Tang and Munkelwitz [1994], and Tang et al…”

“…Secondly, this research provides for the first time the evaluation of closure between experimental measurements and model calculations with respect to the direct dependence of n on RH for the aqueous solutions containing inorganic, organic and mixtures of inorganic and organic solutes. (Tang [1997] presented a closure study for mixed aqueous salt solution droplets comparing the refractive indices calculated by the The relative humidity where the particle starts to absorb a significant amount of water.…”