Experimental evidence for excess entropy discontinuities in glass-forming solutions

Lienhard, Daniel M.; Zobrist, B.; Zuend, Andreas; Krieger, Ulrich K.; Peter, Thomas

doi:10.1063/1.3685902

Cited by 25 publications

(51 citation statements)

References 90 publications

(78 reference statements)

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“…These organics were chosen because they have similar functionality to soluble organic material commonly found in tropospheric aerosol particles (Graham et al, 2003) and have been used in previous investigations of glassy aerosol (Bones et al, 2012;Murray et al, 2010;Zobrist et al, 2008Zobrist et al, , 2011Lienhard et al, 2012;Koop et al, 2011). Tropospheric aerosol often consists of organic material internally mixed with significant fractions of inorganic compounds (e.g., Cziczo et al, 2004;and Murphy et al, 2006).…”

Section: Methodsmentioning

confidence: 99%

State transformations and ice nucleation in amorphous (semi-)solid organic aerosol

et al. 2013

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Abstract. Amorphous (semi-)solid organic aerosol particles have the potential to serve as surfaces for heterogeneous ice nucleation in cirrus clouds. Raman spectroscopy and optical microscopy have been used in conjunction with a cold stage to examine water uptake and ice nucleation on individual amorphous (semi-)solid particles at atmospherically relevant temperatures (200–273 K). Three organic compounds considered proxies for atmospheric secondary organic aerosol (SOA) were used in this investigation: sucrose, citric acid and glucose. Internally mixed particles consisting of each organic and ammonium sulfate were also investigated. Results from water uptake experiments followed the shape of a humidity-induced glass transition (Tg(RH)) curve and were used to construct state diagrams for each organic and corresponding mixture. Experimentally derived Tg(RH) curves are in good agreement with theoretical predictions of Tg(RH) following the approach of Koop et al. (2011). A unique humidity-induced glass transition point on each state diagram, Tg'(RH), was used to quantify and compare results from this study to previous works. Values of Tg'(RH) determined for sucrose, glucose and citric acid glasses were 236, 230 and 220 K, respectively. Values of Tg'(RH) for internally mixed organic/sulfate particles were always significantly lower; 210, 207 and 215 K for sucrose/sulfate, glucose/sulfate and citric acid/sulfate, respectively. All investigated SOA proxies were observed to act as heterogeneous ice nuclei at tropospheric temperatures. Heterogeneous ice nucleation on pure organic particles occurred at Sice = 1.1–1.4 for temperatures below 235 K. Particles consisting of 1:1 organic-sulfate mixtures took up water over a greater range of conditions but were in some cases also observed to heterogeneously nucleate ice at temperatures below 202 K (Sice= 1.25–1.38). Polynomial curves were fitted to experimental water uptake data and then incorporated into the Community Aerosol Radiation Model for Atmospheres (CARMA) along with the predicted range of humidity-induced glass transition temperatures for atmospheric SOA from Koop et al. (2011). Model results suggest that organic and organic/sulfate aerosol could be glassy more than 60% of the time in the midlatitude upper troposphere and more than 40% of the time in the tropical tropopause region (TTL). At conditions favorable for ice formation (Sice > 1), particles in the TTL are expected to be glassy more than 50% of the time for temperatures below 200 K. Results from this study suggests that amorphous (semi-)solid organic particles are often present in the upper troposphere and that heterogeneous ice formation on this type of particle may play an important role in cirrus cloud formation.

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Section: Methodsmentioning

confidence: 99%

State transformations and ice nucleation in amorphous (semi-)solid organic aerosol

et al. 2013

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“…It should also be noted that the water content in terms of mass fractions appears as relatively low, due to the large difference in molar mass of H 2 O compared to the organics; the water content in terms of mole fractions is much higher: ∼ 50 % in the organic phase at 60 % RH and ∼ 38 % at 40 % RH. This is enough water to significantly influence the overall viscosity in the organic phase and prevent a glass transition, at least at higher relative humidities Lienhard et al, 2012).…”

Section: Loading Effects and Water Contentmentioning

confidence: 99%

“…A transition of a liquid PM to a semi-solid or amorphous solid state is also more likely to occur at lower RH (below the 30 % RH range boundary), due to the plasticizer effect of water on the glass transition of partially hygroscopic organic mixtures (e.g. Koop et al, 2011;Lienhard et al, 2012). To address effects of PM mass on gas-particle partitioning, three atmospherically relevant SOA mass loading levels are considered: high loading (∼23 µg m −3 ), moderate loading (∼5 µg m −3 ), and low loading (∼0.9 µg m −3 ) of SOA.…”

Section: Phase Separation and Rh-dependence In Salt-containing Systemmentioning

confidence: 99%

“…Such a semi-solid or amorphous solid state effectively impedes gas-particle mass transfer and bulk diffusion in aerosolswith important consequences for heterogeneous chemistry, aerosol growth and evaporation behavior, and characteristic equilibration times (Tong et al, 2011;Shiraiwa et al, 2011). However, the dilution and plasticizer effects due to mixing of complex organic solutions with low-viscosity compounds like water, may substantially decrease the glass transition temperature of an initially dry mixture at higher relative humidity in case of (slightly) hygroscopic aerosols Lienhard et al, 2012).…”

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Modeling the gas-particle partitioning of secondary organic aerosol: the importance of liquid-liquid phase separation

2012

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Abstract. The partitioning of semivolatile organic compounds between the gas phase and aerosol particles is an important source of secondary organic aerosol (SOA). Gasparticle partitioning of organic and inorganic species is influenced by the physical state and water content of aerosols, and therefore ambient relative humidity (RH), as well as temperature and organic loading levels. We introduce a novel combination of the thermodynamic models AIOMFAC (for liquid mixture non-ideality) and EVAPORATION (for pure compound vapor pressures) with oxidation product information from the Master Chemical Mechanism (MCM) for the computation of gas-particle partitioning of organic compounds and water. The presence and impact of a liquid-liquid phase separation in the condensed phase is calculated as a function of variations in relative humidity, organic loading levels, and associated changes in aerosol composition. We show that a complex system of water, ammonium sulfate, and SOA from the ozonolysis of α-pinene exhibits liquid-liquid phase separation over a wide range of relative humidities (simulated from 30 % to 99 % RH). Since fully coupled phase separation and gas-particle partitioning calculations are computationally expensive, several simplified model approaches are tested with regard to computational costs and accuracy of predictions compared to the benchmark calculation. It is shown that forcing a liquid one-phase aerosol with or without consideration of non-ideal mixing bears the potential for vastly incorrect partitioning predictions. Assuming an ideal mixture leads to substantial overestimation of the particulate organic mass, by more than 100 % at RH values of 80 % and by more than 200 % at RH values of 95 %. Moreover, the simplified one-phase cases stress two key points for accurate gas-particle partitioning calculations: (1) non-ideality in the condensed phase needs to be considered and (2) liquidliquid phase separation is a consequence of considerable deviations from ideal mixing in solutions containing inorganic ions and organics that cannot be ignored. Computationally much more efficient calculations relying on the assumption of a complete organic/electrolyte phase separation below a certain RH successfully reproduce gas-particle partitioning in systems in which the average oxygen-to-carbon (O:C) ratio is lower than ∼0.6, as in the case of α-pinene SOA, and bear the potential for implementation in atmospheric chemical transport models and chemistry-climate models. A full equilibrium calculation is the method of choice for accurate offline (box model) computations, where high computational costs are acceptable. Such a calculation enables the most detailed predictions of phase compositions and provides necessary information on whether assuming a complete organic/electrolyte phase separation is a good approximation for a given aerosol system. Based on the group-contribution concept of AIOMFAC and O:C ratios as a proxy for polarity and hygroscopicity of organic mixtures, the results from the α-pinene system are ...

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“…e Based on a Gordon-Taylor fit (Gordon and Taylor, 1952) between T g of levoglucosan and T g of NH 4 HSO 4 taken from Zobrist et al (2008). f From Lienhard et al (2012b). g From Dette et al (2014).…”

Section: A2 Parameterization Of D W (T a W )mentioning

confidence: 99%

Viscous organic aerosol particles in the upper troposphere: diffusivity-controlled water uptake and ice nucleation?

Lienhard

Huisman

Krieger³

et al. 2015

Atmos. Chem. Phys.

119

193

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Abstract. New measurements of water diffusion in secondary organic aerosol (SOA) material produced by oxidation of α-pinene and in a number of organic/inorganic model mixtures (3-methylbutane-1,2,3-tricarboxylic acid (3-MBTCA), levoglucosan, levoglucosan/NH 4 HSO 4 , raffinose) are presented. These indicate that water diffusion coefficients are determined by several properties of the aerosol substance and cannot be inferred from the glass transition temperature or bouncing properties. Our results suggest that water diffusion in SOA particles is faster than often assumed and imposes no significant kinetic limitation on water uptake and release at temperatures above 220 K. The fast diffusion of water suggests that heterogeneous ice nucleation on a glassy core is very unlikely in these systems. At temperatures below 220 K, model simulations of SOA particles suggest that heterogeneous ice nucleation may occur in the immersion mode on glassy cores which remain embedded in a liquid shell when experiencing fast updraft velocities. The particles absorb significant quantities of water during these updrafts which plasticize their outer layers such that these layers equilibrate readily with the gas phase humidity before the homogeneous ice nucleation threshold is reached. Glass formation is thus unlikely to restrict homogeneous ice nucleation. Only under most extreme conditions near the very high tropical tropopause may the homogeneous ice nucleation rate coefficient be reduced as a consequence of slow condensed-phase water diffusion. Since the differences between the behavior limited or non limited by diffusion are small even at the very high tropical tropopause, condensed-phase water diffusivity is unlikely to have significant consequences on the direct climatic effects of SOA particles under tropospheric conditions.

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Experimental evidence for excess entropy discontinuities in glass-forming solutions

Cited by 25 publications

References 90 publications

State transformations and ice nucleation in amorphous (semi-)solid organic aerosol

State transformations and ice nucleation in amorphous (semi-)solid organic aerosol

Modeling the gas-particle partitioning of secondary organic aerosol: the importance of liquid-liquid phase separation

Viscous organic aerosol particles in the upper troposphere: diffusivity-controlled water uptake and ice nucleation?

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