New and extended parameterization of the thermodynamic model AIOMFAC: calculation of activity coefficients for organic-inorganic mixtures containing carboxyl, hydroxyl, carbonyl, ether, ester, alkenyl, alkyl, and aromatic functional groups

Abstract

Abstract. We present a new and considerably extended parameterization of the thermodynamic activity coefficient model AIOMFAC (Aerosol Inorganic-Organic Mixtures Functional groups Activity Coefficients) at room temperature. AIOMFAC combines a Pitzer-like electrolyte solution model with a UNIFAC-based group-contribution approach and explicitly accounts for interactions between organic functional groups and inorganic ions. Such interactions constitute the salt-effect, may cause liquid-liquid phase separation, and affect the gas-particle partitioning of aerosols. The previous AIOMFAC version was parameterized for alkyl and hydroxyl functional groups of alcohols and polyols. With the goal to describe a wide variety of organic compounds found in atmospheric aerosols, we extend here the parameterization of AIOMFAC to include the functional groups carboxyl, hydroxyl, ketone, aldehyde, ether, ester, alkenyl, alkyl, aromatic carbon-alcohol, and aromatic hydrocarbon. Thermodynamic equilibrium data of organic-inorganic systems from the literature are critically assessed and complemented with new measurements to establish a comprehensive database. The database is used to determine simultaneously the AIOMFAC parameters describing interactions of organic functional groups with the ions H+, Li+, Na+, K+, NH4+, Mg2+, Ca2+, Cl−, Br−, NO3−, HSO4−, and SO42−. Detailed descriptions of different types of thermodynamic data, such as vapor-liquid, solid-liquid, and liquid-liquid equilibria, and their use for the model parameterization are provided. Issues regarding deficiencies of the database, types and uncertainties of experimental data, and limitations of the model, are discussed. The challenging parameter optimization problem is solved with a novel combination of powerful global minimization algorithms. A number of exemplary calculations for systems containing atmospherically relevant aerosol components are shown. Amongst others, we discuss aqueous mixtures of ammonium sulfate with dicarboxylic acids and with levoglucosan. Overall, the new parameterization of AIOMFAC agrees well with a large number of experimental datasets. However, due to various reasons, for certain mixtures important deviations can occur. The new parameterization makes AIOMFAC a versatile thermodynamic tool. It enables the calculation of activity coefficients of thousands of different organic compounds in organic-inorganic mixtures of numerous components. Models based on AIOMFAC can be used to compute deliquescence relative humidities, liquid-liquid phase separations, and gas-particle partitioning of multicomponent mixtures of relevance for atmospheric chemistry or in other scientific fields.

Gas–particle partitioning of atmospheric aerosols: interplay of physical state, non-ideal mixing and morphology

“…Non-ideal thermodynamic mixing in the condensed phase is considered via composition-dependent activity coefficients, calculated with the AIOMFAC model (Aerosol Inorganic-Organic Mixtures Functional groups Activity Coefficients). 29,30 This group-contribution model explicitly considers interactions between all components (and their functional groups) present in a mixture, including interactions between dissolved inorganic ions and organic functional groups.…”

“…The potential for a liquid-liquid phase separation is accounted for and corresponding phase compositions are calculated with the practical method of Zuend and Seinfeld. 28 Solid-liquid equilibrium between crystalline and dissolved AS is calculated based on the conditions of a constant ion activity product (IAP) of a saturated solution in equilibrium with a solid phase at given temperature: 30 SO 4 ] is calculated from the measured solubility limit of AS in water (at the same temperature). 64 In the case of the aerosol system shown in Fig.…”

“…The humidity cycle is calculated using the thermodynamic model AIOMFAC. 29,30 (c) Examples of phases and morphologies. A predominantly organic phase is colored green (dark green for amorphous solid); a predominantly aqueous electrolyte-rich phase is shown in blue.…”

“…1b, predicted using a thermodynamic equilibrium model based on AIOMFAC (Aerosol Inorganic-Organic Mixtures Functional groups Activity Coefficients) (details given in Appendix A). 29,30 The mass change with increasing RH results from the uptake of water accompanied by a change in the gas-particle partitioning of the organic components. The amount of water uptake depends on whether ammonium sulfate is present predominantly in solid form or whether the electrolyte is completely dissolved in an aqueous solution; the latter is the case above the deliquescence point (solubility limit) of ammonium sulfate in this system, here at RH B 80%.…”

Surface tension prevails over solute effect in organic-influenced cloud droplet activation

“…Thermodynamic equilibrium calculations were performed by application of a coupled LLPS and gas-particle partitioning framework 61,64 on the basis of activity coefficients computed by the Aerosol Inorganic-Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model 50,51 . The AIOMFAC model uses a group-contribution concept to describe the non-ideal mixing behaviour of multifunctional organic compounds, water and inorganic ions.…”