Experimental determination of the temperature dependence of water activities for a selection of aqueous organic solutions

Abstract

Abstract. This work presents experimental data of the temperature dependence of water activity in aqueous organic solutions relevant for tropospheric conditions (200-273 K). Water activity (a w ) at low temperatures (T ) is a crucial parameter for predicting homogeneous ice nucleation. We investigated temperature-dependent water activities, ice freezing and melting temperatures of solutions, and vapour pressures of a selection of atmospherically relevant aqueous organic systems. To measure a w over a wide composition range and with a focus on low temperatures, we use various a w measurement techniques and instruments: a dew point water activity meter, an electrodynamic balance (EDB), differential scanning calorimetry (DSC), and a setup to measure the total gas phase pressure at equilibrium over aqueous solutions. Water activity measurements were performed for aqueous multicomponent and multifunctional organic mixtures containing the functional groups typically found in atmospheric organic aerosols, such as hydroxyl, carboxyl, ketone, ether, ester, and aromatic groups. The aqueous organic systems studied at several fixed compositions over a considerable temperature range differ significantly in their temperature dependence. Aqueous organic systems of 1,4-butanediol and methoxyacetic acid show a moderate decrease in a w with decreasing temperature. The aqueous M5 system (a multicomponent system containing five different dicarboxylic acids) and aqueous 2-(2-ethoxyethoxy)ethanol solutions both show a strong increase of water activity with decreasing temperature at high solute concentrations for T < 270 K and T < 260 K, respectively. These measurements show that the temperature trend of a w can be reversed at low temperatures and that linear extrapolations of high-temperature data may lead to erroneous predictions. To avoid this, experimentally determined a w at low temperature are needed to improve thermodynamic models towards lower temperatures and for improved predictions of the ice nucleation ability of organicwater systems.

Improved AIOMFAC model parameterisation of the temperature dependence of activity coefficients for aqueous organic mixtures

“…d SLE data where the equilibrium is with respect to an organic compound in a solid (crystalline) state. e Derived water activity data from total pressure measurements, for more information we refer to Ganbavale et al (2014). f Derived water activity data from electrodynamic balance (EDB) measurements, for more information we refer to Ganbavale et al (2014).…”

“…Water activity data for measured binary aqueous organic bulk solutions are tabulated in Tables A1-A8. Additional measurements of aqueous multi-functional organic solutions are provided in Ganbavale et al (2014). Measured water activities were then used directly for the AIOMFAC-P3 parameter determination -with the exception of data within ±10 K from 298 K.…”

Compositional evolution of particle-phase reaction products and water in the heterogeneous OH oxidation of model aqueous organic aerosols

“…Depending on the particle composition and environmental conditions, such as RH and temperature, particle-phase water can be an important component of aqueous organic droplets (Peng et al, 2001;Brooks et al, 2002;Braban et al, 2003;Marcolli et al, 2004;Mochida and Kawamura, 2004;Parsons et al, 2004;Chan et al, 2005Chan et al, , 2008Mikhailov et al, 2009;Ma et al, 2013;Ganbavale et al, 2014;Chen et al, 2015;Jing et al, 2016). Upon oxidation, the amount of particlephase water can continuously vary in response to changes in particle composition.…”

Preferential solvation of etoricoxib in some aqueous binary cosolvent mixtures at 298.15 K

“…The required physicochemical properties for 1,4-dioxane (1) + water (2) and ethanol (1) + water (2) mixtures have been reported in one of our earlier publications. [12] In turn, G Exc 1þ2 values (expressed in J mol -1 ) were calculated for the remaining four cosolvent (1) + mixtures (2) based on data reported in the literature as follows: for N,N-dimethylacetamide (1) + water (2) mixtures by means of Equation (13) (obtained from measured data contained in [21] and [22]); for 1,4-butanediol (1) + water (2) mixtures by means of Equation (14) (obtained from published data from [23]); for N,N-dimethylformamide (1) + water (2) by means of Equation (15) (obtained from data reported in [24] and [25]); and for dimethyl sulfoxide (1) + water (2) by means of Equation (16) (obtained from data reported in [19]). In all four equations, x 1 represents the mole fraction of the cosolvent.…”