The Water Activities of MgCl2, Mg(NO3)2, MgSO4, and Their Mixtures

Ha, Zhanyao; Chan, Chak Keung

doi:10.1080/027868299304219

Cited by 90 publications

(109 citation statements)

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“…The equilibrium time of a few seconds is adequate for equilibrium particle growth/evaporation in typical inorganic salt particles such as NaCl and (NH 4 ) 2 SO 4 , but it may not be adequate for other particles such as those coated with organic layers. Chan and coworkers have found significant mass transfer effects in EDB hygroscopicity measurements for some inorganic salt particles such as MgSO 4 (Ha and Chan, 1999;Zhang and Chan, 2000) and organic particles such as sodium pyruvate, arginine, and asparagine Chan et al, 2005). Although particles studied in the EDB are 2 orders of magnitude larger and would take a longer equilibration time than those studied in the TDMA, these results suggest the possibility that longer equilibrium time scales may be required for TDMA measurements of these single or multicomponent particles, as discussed for glutaric acid particles earlier.…”

Section: Discussionmentioning

confidence: 99%

Mass transfer effects in hygroscopic measurements of aerosol particles

Chan

2005

Atmos. Chem. Phys.

100

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Abstract.The tandem differential mobility analyzer (TDMA) has been widely utilized to measure the hygroscopicity of laboratory-generated and atmospheric submicrometer particles. An important concern in investigating the hygroscopicity of the particles is if the particles have attained equilibrium state in the measurements. We present a literature survey to investigate the mass transfer effects in hygroscopicity measurements. In most TDMA studies, a residence time in the order of seconds is used for humidification (or dehumidification). NaCl and (NH 4 ) 2 SO 4 particles are usually used to verify the equilibrium measurements during this residence time, which is presumed to be sufficient for other particles. There have been observations that not all types of submicrometer particles, including atmospheric particles, attain their equilibrium sizes within this time scale. We recommend that experimentation with different residence times be conducted and that the residence time should be explicitly stated in future TDMA measurements. Mass transfer effects may also exist in the measurements of other properties related to the water uptake of atmospheric particles such as relative humidity dependent light scattering coefficients and cloud condensation nuclei activity.

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Section: Discussionmentioning

confidence: 99%

Mass transfer effects in hygroscopic measurements of aerosol particles

Chan

2005

Atmos. Chem. Phys.

100

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“…Mg-rich coatings are amorphous. Although characteristics of Mg-rich components (e.g., Mg(NO 3 ) 2 , MgSO 4 , and MgCl 2 ) were studied in laboratory experiments (Ha and Chan, 1999;Li et al, 2008), the association of Mg-rich coatings with mineral particles is very limited in field studies. We believe that Mg-rich coatings are possibly mixtures of Mg(NO 3 ) 2 and Mg-bearing sulfates as well as minor chlorides (i.e., MgCl 2 and CaCl 2 ).…”

Section: Ca-rich Coatingmentioning

confidence: 99%

Observation of nitrate coatings on atmospheric mineral dust particles

2009

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Abstract. Nitrate compounds have received much attention because of their ability to alter the hygroscopic properties and cloud condensation nuclei (CCN) activity of mineral dust particles in the atmosphere. However, very little is known about specific characteristics of ambient nitratecoated mineral particles on an individual particle scale. In this study, sample collection was conducted during brown haze and dust episodes between 24 May and 21 June 2007 in Beijing, northern China. Sizes, morphologies, and compositions of 332 mineral dust particles together with their coatings were analyzed using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray (EDX) microanalyses. Structures of some mineral particles were verified using selected-area electron diffraction (SAED). TEM observation indicates that approximately 90% of the collected mineral particles are covered by visible coatings in haze samples whereas only 5% are coated in the dust sample. 92% of the analyzed mineral particles are covered with Ca-, Mg-, and Na-rich coatings, and 8% are associated with K-and S-rich coatings. The majority of coatings contain Ca, Mg, O, and N with minor amounts of S and Cl, suggesting that they are possibly nitrates mixed with small amounts of sulfates and chlorides. These nitrate coatings are strongly correlated with the presence of alkaline mineral components (e.g., calcite and dolomite). CaSO 4 particles with diameters from 10 to 500 nm were also detected in the coatings including Ca(NO 3 ) 2 and Mg(NO 3 ) 2 . Our results indicate that mineral particles in brown haze episodes were involved in atmospheric heteroCorrespondence to: L. Y. Shao (shaol@cumtb.edu.cn) geneous reactions with two or more acidic gases (e.g., SO 2 , NO 2 , HCl, and HNO 3 ). Mineral particles that acquire hygroscopic nitrate coatings tend to be more spherical and larger, enhancing their light scattering and CCN activity, both of which have cooling effects on the climate.

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“…2). For these cases the DRH of NH 4 NO 3(s) in ISOR-ROPIA II is assumed to not "cross over" the DRH of the other salts present in the solution, especially Ha and Chan (1999) since thermodynamic data for supercooled NH 4 NO 3(s) solutions are not known. The same is assumed for NH 4 Cl (s) and NaNO 3(s) which exhibit similar behavior with NH 4 NO 3(s) (Fig.…”

Section: Simplifications and Assumptions In Isorropia IImentioning

confidence: 99%

“…13) are shown in Table 4. displays the polynomial fit parameters for computing the molalities of binary solutions as a function of water activity (obtained from Kim and Seinfeld, 1995;Ha and Chan, 1999;Wexler, 2005, 2006) 4 Cl, NaCl, NaNO 3 , NaHSO 4 and Na 2 SO 4 , the water activity database was updated since the original release of ISORROPIA, using the output from the AIM model (http://www.hpc1.uea.ac.uk/ ∼ e770/aim.html).…”

Section: Solution Proceduresmentioning

confidence: 99%

ISORROPIA II: a computationally efficient thermodynamic equilibrium model for K+–Ca2+–Mg2+–NH4+–Na+–SO42−–NO3−–Cl<

2007

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Abstract. This study presents ISORROPIA II, a thermodynamic equilibrium model for the K+–Ca2+–Mg2+–NH4+–Na+–SO42−–NO3−–Cl−–H2O aerosol system. A comprehensive evaluation of its performance is conducted against water uptake measurements for laboratory aerosol and predictions of the SCAPE2 thermodynamic module over a wide range of atmospherically relevant conditions. The two models agree well, to within 13% for aerosol water content and total PM mass, 16% for aerosol nitrate and 6% for aerosol chloride and ammonium. Largest discrepancies were found under conditions of low RH, primarily from differences in the treatment of water uptake and solid state composition. In terms of computational speed, ISORROPIA II was more than an order of magnitude faster than SCAPE2, with robust and rapid convergence under all conditions. The addition of crustal species does not slow down the thermodynamic calculations (compared to the older ISORROPIA code) because of optimizations in the activity coefficient calculation algorithm. Based on its computational rigor and performance, ISORROPIA II appears to be a highly attractive alternative for use in large scale air quality and atmospheric transport models.

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The Water Activities of MgCl₂, Mg(NO₃)₂, MgSO₄, and Their Mixtures

Cited by 90 publications

References 0 publications

Mass transfer effects in hygroscopic measurements of aerosol particles

Mass transfer effects in hygroscopic measurements of aerosol particles

Observation of nitrate coatings on atmospheric mineral dust particles

ISORROPIA II: a computationally efficient thermodynamic equilibrium model for K<sup>+</sup>–Ca<sup>2+</sup>–Mg<sup>2+</sup>–NH<sub>4</sub><sup>+</sup>–Na<sup>+</sup>–SO<sub>4</sub><sup>2−</sup>–NO<sub>3</sub><sup>−</sup>–Cl<

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