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Calculation of Activity Coefficients for Organic-Inorganic

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Calculation of Activity Coefficients for Organic-Inorganic Atmos. Chem. Phys., 11, 9155–9206, 2011 www.atmos-chem-phys.net/11/9155/2011/ Atmospheric doi:10.5194/acp-11-9155-2011 Chemistry © Author(s) 2011. CC Attribution 3.0 License. and Physics 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 A. Zuend1, C. Marcolli2, A. M. Booth3, D. M. Lienhard2,4, V. Soonsin2, U. K. Krieger2, D. O. Topping3, G. McFiggans3, T. Peter2, and J. H. Seinfeld1 1Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA 2Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland 3School of Earth, Environmental and Atmospheric Science, University of Manchester, Manchester, UK 4School of Chemistry, University of Bristol, Bristol, UK Received: 26 April 2011 – Published in Atmos. Chem. Phys. Discuss.: 20 May 2011 Revised: 25 August 2011 – Accepted: 1 September 2011 – Published: 7 September 2011 Abstract. We present a new and considerably extended as vapor-liquid, solid-liquid, and liquid-liquid equilibria, and parameterization of the thermodynamic activity coefficient their use for the model parameterization are provided. Is- model AIOMFAC (Aerosol Inorganic-Organic Mixtures sues regarding deficiencies of the database, types and uncer- Functional groups Activity Coefficients) at room tempera- tainties of experimental data, and limitations of the model, ture. AIOMFAC combines a Pitzer-like electrolyte solu- are discussed. The challenging parameter optimization prob- tion model with a UNIFAC-based group-contribution ap- lem is solved with a novel combination of powerful global proach and explicitly accounts for interactions between or- minimization algorithms. A number of exemplary calcula- ganic functional groups and inorganic ions. Such interactions tions for systems containing atmospherically relevant aerosol constitute the salt-effect, may cause liquid-liquid phase sep- components are shown. Amongst others, we discuss aque- aration, and affect the gas-particle partitioning of aerosols. ous mixtures of ammonium sulfate with dicarboxylic acids The previous AIOMFAC version was parameterized for alkyl and with levoglucosan. Overall, the new parameterization of and hydroxyl functional groups of alcohols and polyols. AIOMFAC agrees well with a large number of experimental With the goal to describe a wide variety of organic com- datasets. However, due to various reasons, for certain mix- pounds found in atmospheric aerosols, we extend here the pa- tures important deviations can occur. The new parameteri- rameterization of AIOMFAC to include the functional groups zation makes AIOMFAC a versatile thermodynamic tool. It carboxyl, hydroxyl, ketone, aldehyde, ether, ester, alkenyl, enables the calculation of activity coefficients of thousands alkyl, aromatic carbon-alcohol, and aromatic hydrocarbon. of different organic compounds in organic-inorganic mix- Thermodynamic equilibrium data of organic-inorganic sys- tures of numerous components. Models based on AIOMFAC tems from the literature are critically assessed and comple- can be used to compute deliquescence relative humidities, mented with new measurements to establish a comprehensive liquid-liquid phase separations, and gas-particle partitioning database. The database is used to determine simultaneously of multicomponent mixtures of relevance for atmospheric the AIOMFAC parameters describing interactions of organic chemistry or in other scientific fields. + + + + + functional groups with the ions H , Li , Na ,K , NH4 , 2+ 2+ − − − − 2− Mg , Ca , Cl , Br , NO3 , HSO4 , and SO4 . Detailed descriptions of different types of thermodynamic data, such Correspondence to: A. Zuend ([email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union. 9156 A. Zuend et al.: Extended parameterization of the AIOMFAC model 1 Introduction Activity coefficients of the different components represent the degree of thermodynamic non-ideality in a specific mul- Thermodynamic models are key tools to gain insight into ticomponent mixture, caused by the combined effects of all the non-ideal behavior of organic-inorganic mixtures. At- molecular interactions. For atmospheric purposes the vapor mospheric aerosols present prominent examples for organic- pressures of water and semivolatile organic and inorganic inorganic mixtures of remarkable complexity, containing a compounds are required in gas-particle partitioning calcula- multitude of different organic compounds, inorganic salts tions, which depend on the saturation vapor pressures of the and acids, and water (e.g., Rogge et al., 1993; Saxena and pure compounds and their activity coefficients in the liquid Hildemann, 1996; Murphy and Thomson, 1997; Middle- aerosol mixture. For example, in case of water, the equilib- brook et al., 1998; Decesari et al., 2000; Lee et al., 2002; rium water vapor pressure over a liquid mixture, pw, is re- Griffin et al., 2002; Maria et al., 2004; Kanakidou et al., lated to the water activity on the mole fraction basis (denoted 2005; Murphy et al., 2006; Decesari et al., 2006; Zhang (x) ◦ (x) ◦ by superscript (x)), aw , by pw = pwaw , where pw is the et al., 2007; Russell et al., 2009). Gas-particle partitioning saturation vapor pressure over pure liquid water (a function of water and semivolatile organic and inorganic compounds (x) of temperature only). Activity and activity coefficient, γs , is determined by thermodynamic equilibrium between the of a compound s are related by a(x) = γ (x)x , where x is gaseous and condensed phases (Pankow, 1994, 2003; Hal- s s s s the mole fraction of s in the liquid mixture. These basic ther- lquist et al., 2009; Zuend et al., 2010) and by the kinetics modynamic relationships, corresponding chemical potentials of exchange processes such as gas phase diffusion (Mar- and standard states, are described in detail by Zuend et al. colli et al., 2004b). The non-ideality of mixtures in aerosol (2010). In case of atmospheric water at gas-particle equi- particles influences the gas-particle partitioning and affects librium, relative humidity and aerosol water activity are re- the physical state of the condensed phase, potentially lead- = (x) = (x) ing to liquid-liquid phase separation (Pankow, 2003; Erdakos lated by RH aw γw xw (strictly valid only for droplet and Pankow, 2004; Marcolli and Krieger, 2006; Chang and sizes where the Kelvin effect due to the curvature of the sur- Pankow, 2006; Ciobanu et al., 2009; Zuend et al., 2010; face can be neglected, i.e., for droplet diameters >100 nm). Kwamena et al., 2010; Smith et al., 2011; Bertram et al., At the core of thermodynamic equilibrium calculations are 2011), the formation of crystalline solid phases (Nenes et al., therefore models to calculate activity coefficients. 1998; Clegg et al., 1998a; Colberg et al., 2004; Zaveri et al., In the past, the development of activity coefficient models 2005; Fountoukis and Nenes, 2007), or the transition to an mainly evolved in two categories: (1) models for (organic- amorphous solid state (Zobrist et al., 2008, 2011; Murray, free) aqueous electrolyte solutions or for (electrolyte-free) 2008; Mikhailov et al., 2009; Virtanen et al., 2010). aqueous organic mixtures, and (2) models for mixed organic- Inorganic salts and acids (electrolytes) that for the most inorganic systems. In category (1), a number of success- part dissociate into ions (charged molecules or atoms) in ful models for calculating thermodynamic aerosol proper- liquid solutions play an important role in aqueous organic- ties of aqueous electrolyte mixtures have been developed inorganic systems. Interactions between ions and neutral or- based on Pitzer’s extension of the Debye-Huckel¨ theory ganic molecules may have a crucial impact on the dissolu- and the Pitzer-Simonson-Clegg approach (e.g., Clegg and tion behavior and phase state of a system, commonly known Pitzer, 1992; Clegg et al., 1992; Carslaw et al., 1995; Clegg as the salt-effect: Increasing the concentration of a strong et al., 1998a,b; Topping et al., 2005a; Amundson et al., electrolyte in a mixture may lead to “salting-out” of rela- 2006; Zuend et al., 2008) or the Kusik-Meissner relation- tively nonpolar organics, i.e., the dissolved ions drive the or- ship and Bromley’s formula (Nenes et al., 1998; Fountoukis ganic compounds out of the mixed phase – either to the gas and Nenes, 2007). Aerosol models for mixtures of organics phase or into a different, organic-rich liquid phase, initiat- and water are most often based on the UNIQUAC (UNIver- ing or modifying a liquid-liquid phase separation and a new sal QUAsi Chemical) model (Abrams and Prausnitz, 1975) equilibrium state. This well-known property of electrolytes or its group-contribution version UNIFAC (UNIquac Func- is used in chemical and biochemical process engineering to tional group Activity Coefficients) (Fredenslund et al., 1975; separate aqueous organic mixtures (liquid-liquid extraction, Hansen et al., 1991). Models for organic-inorganic mix- two-phase partitioning) and to shift azeotropes in distillation tures are generally composed of an aqueous electrolyte term, processes, with large-scale applications in the petrochemical an (aqueous) organic term, and an organic-ion mixing term industry, in seawater desalination plants, and water purifi- (Tong et al., 2008). In category (2), models for organic- cation systems. With respect to tropospheric
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