ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-13-717-2013 Mass-based hygroscopicity parameter interaction model and measurement of atmospheric aerosol water uptake Mikhailov E. 1 2 Vlasenko S. 2 Rose D. 1 Pöschl U. 1 Multiphase Chemistry and Biogeochemisty Departments, Max Planck Institute for Chemistry, Mainz, Germany Atmospheric Physics Department, Institute of Physics, St. Petersburg State University, St. Petersburg, Russia 21 01 2013 13 2 717 740 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/13/717/2013/acp-13-717-2013.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/13/717/2013/acp-13-717-2013.pdf

In this study we derive and apply a mass-based hygroscopicity parameter interaction model for efficient description of concentration-dependent water uptake by atmospheric aerosol particles with complex chemical composition. The model approach builds on the single hygroscopicity parameter model of Petters and Kreidenweis (2007). We introduce an observable mass-based hygroscopicity parameter &kappa;<sub>m</sub> which can be deconvoluted into a dilute hygroscopicity parameter (&kappa;<sub>m</sub><sup>0</sup>) and additional self- and cross-interaction parameters describing non-ideal solution behavior and concentration dependencies of single- and multi-component systems. <br><br> For reference aerosol samples of sodium chloride and ammonium sulfate, the &kappa;<sub>m</sub>-interaction model (KIM) captures the experimentally observed concentration and humidity dependence of the hygroscopicity parameter and is in good agreement with an accurate reference model based on the Pitzer ion-interaction approach (Aerosol Inorganic Model, AIM). Experimental results for pure organic particles (malonic acid, levoglucosan) and for mixed organic-inorganic particles (malonic acid – ammonium sulfate) are also well reproduced by KIM, taking into account apparent or equilibrium solubilities for stepwise or gradual deliquescence and efflorescence transitions. <br><br> The mixed organic-inorganic particles as well as atmospheric aerosol samples exhibit three distinctly different regimes of hygroscopicity: (I) a quasi-eutonic deliquescence & efflorescence regime at low-humidity where substances are just partly dissolved and exist also in a non-dissolved phase, (II) a gradual deliquescence & efflorescence regime at intermediate humidity where different solutes undergo gradual dissolution or solidification in the aqueous phase; and (III) a dilute regime at high humidity where the solutes are fully dissolved approaching their dilute hygroscopicity. <br><br> For atmospheric aerosol samples collected from boreal rural air and from pristine tropical rainforest air (secondary organic aerosol) we present first mass-based measurements of water uptake over a wide range of relative humidity (1–99.4%) obtained with a new filter-based differential hygroscopicity analyzer (FDHA) technique. For these samples the concentration dependence of &kappa;<sub>m</sub> can be described by a simple KIM model equation based on observable mass growth factors and a total of only six fit parameters summarizing the combined effects of the dilute hygroscopicity parameters, self- and cross-interaction parameters, and solubilities of all involved chemical components. One of the fit parameters represents &kappa;<sub>m</sub><sup>0</sup> and can be used to predict critical dry diameters for the activation of cloud condensation nuclei (CCN) as a function of water vapor supersaturation according to Köhler theory. For sodium chloride and ammonium sulfate reference particles as well as for pristine rainforest aerosols consisting mostly of secondary organic matter, we obtained good agreement between the KIM predictions and measurement data of CCN activation. <br><br> The application of KIM and mass-based measurement techniques shall help to bridge gaps in the current understanding of water uptake by atmospheric aerosols: (1) the gap between hygroscopicity parameters determined by hygroscopic growth measurements under sub-saturated conditions and by CCN activation measurements at water vapor supersaturation, and (2) the gap between the results of simplified single parameter models widely used in atmospheric or climate science and the results of complex multi-parameter ion- and molecule-interaction models frequently used in physical chemistry and solution thermodynamics (e.g., AIM, E-AIM, ADDEM, UNIFAC, AIOMFAC).

 References Bilde, M. and Svenningsson, B.: CCN activation of slightly soluble organics: the importance of small amounts of inorganic salt and particle phase, Tellus B, 56, 128–134, 2004. Biskos, G., Paulsen, D., Russell, L. M., Buseck, P. R., and Martin, S. T.: Prompt deliquescence and efflorescence of aerosol nanoparticles, Atmos. Chem. Phys., 6, 4633–4642, http://dx.doi.org/10.5194/acp-6-4633-2006doi:10.5194/acp-6-4633-2006, 2006. Braban, C. F. and Abbatt, J. P. D.: A study of the phase transition behavior of internally mixed ammonium sulfate – malonic acid aerosols, Atmos. Chem. Phys., 4, 1451–1459, http://dx.doi.org/10.5194/acp-4-1451-2004doi:10.5194/acp-4-1451-2004, 2004. Brooks, S. D., Wise, M. E., Cushing, M., and Tolbert, M. A.: Deliquescence of organic/ammonium sulfate aerosol, Geophys. Res. Lett., 29, 1917, http://dx.doi.org/10.1029/2002GL014733doi:10.1029/2002GL014733, 2002. Carrico, C. M., Petters, M. D., Kreidenweis, S. M., Sullivan, A. P., McMeeking, G. R., Levin, E. J. T., Engling, G., Malm, W. C., and Collett Jr., J. L.: Water uptake and chemical composition of fresh aerosols generated in open burning of biomass, Atmos. Chem. Phys., 10, 5165–5178, http://dx.doi.org/10.5194/acp-10-5165-2010doi:10.5194/acp-10-5165-2010, 2010. Cerully, K. M., Raatikainen, T., Lance, S., Tkacik, D., Tiitta, P., Petäjä, T., Ehn, M., Kulmala, M., Worsnop, D. R., Laaksonen, A., Smith, J. N., and Nenes, A.: Aerosol hygroscopicity and CCN activation kinetics in a boreal forest environment during the 2007 EUCAARI campaign, Atmos. Chem. Phys., 11, 12369–12386, http://dx.doi.org/10.5194/acp-11-12369-2011doi:10.5194/acp-11-12369-2011, 2011. Chan, M. N., Choi, M. Y., Ng, N. L., and Chan, C. K.: Hygroscopicity of water-soluble organic compounds in atmospheric aerosols: Amino acids and biomass burning derived organic species, Environ. Sci. Technol., 39, 1555–1562, http://dx.doi.org/10.1021/es049584ldoi:10.1021/es049584l, 2005. Chen, Q., Farmer, D. K., Schneider, J., Zorn, S. R., Heald, C. L., Karl, T. G., Guenther, A., Allan, J. D., Robinson, N., Coe, H., Kimmel, J. R., Pauliquevis, T., Borrmann, S., Pöschl, U., Andreae, M. O., Artaxo, P., Jimenez, J. L., and Martin, S. T.: Mass spectral characterization of submicron biogenic organic particles in the Amazon Basin, Geophys. Res. Lett., 36, L20806, http://dx.doi.org/10.1029/2009GL039880doi:10.1029/2009GL039880, 2009. Choi, M. Y. and Chan, C. K.: The effects of organic species on the hygroscopic behaviors of inorganic aerosols, Environ. Sci. Technol., 36, 2422–2428, http://dx.doi.org/10.1021/es0113293doi:10.1021/es0113293, 2002. Ciobanu, V. G., Marcolli, C., Krieger, U. K., Zuend, A., and Peter, T.: Efflorescence of ammonium sulfate and coated ammonium sulfate particles: evidence for surface nucleation, J. Phys. Chem. A, 114, 9486–9495, 2010. Clarke, E. C. W. and Glew, D. N.: Evaluation of the thermodynamic functions for aqueous sodium chloride from equilibrium and calorimetric measurements below 154 °C, J. Phys. Chem. Ref. Data, 14, 489–609, 1985. Clegg, S. L. and Seinfeld, J. H.: Improvement of the Zdanovskii-Stokes-Robinson model for mixtures containing solutes of different charge types, J. Phys. Chem. A, 108, 1008–1017, 2004. Clegg, S. L. and Seinfeld, J. H.: Thermodynamic models of aqueous solutions containing inorganic electrolytes and dicarboxylic Acids at 298.15 K. 1. The acids as nondissociating components, J. Phys. Chem. A., 110, 5692–5717, 2006. Clegg, S. L., Brimblecombe, P., and Wexler, A. S.: A thermodynamic model of the system H$^+$-NH$_4^+$-Na$^+$-SO$_4^2-$-NO$_3^-$-Cl$^-$-H<sub>2</sub>O at 298.15 K, J. Phys. Chem. A., 102, 2155–2171, 1998. Clegg, S. L., Seinfeld, J. H., and Brimblecombe, P.: Thermodynamic modelling of aqueous aerosols containing electrolytes and dissolved organic compounds, Aerosol Sci., 32, 713–738, http://dx.doi.org/10.1016/S0021-8502(00)00105-1doi:10.1016/S0021-8502(00)00105-1, 2001. Clegg, S. L., Seinfeld, J. H., and Edney E. O.: Thermodynamic modelling of aqueous aerosols containing electrolytes and dissolved organic compounds. II. An extended Zdanovskii–Stokes–Robinson approach, Aerosol Sci., 34, 667–690, 2003. Corrigan, C. E. and Novakov, T.: Cloud condensation nucleus activity of organic compounds: a laboratory study, Atmos. Environ., 33, 2661–2668, http://dx.doi.org/10.1016/S1352-2310(98)00310-0doi:10.1016/S1352-2310(98)00310-0, 1999. Duplissy, J., DeCarlo, P. F., Dommen, J., Alfarra, M. R., Metzger, A., Barmpadimos, I., Prevot, A. S. H., Weingartner, E., Tritscher, T., Gysel, M., Aiken, A. C., Jimenez, J. L., Canagaratna, M. R., Worsnop, D. R., Collins, D. R., Tomlinson, J., and Baltensperger, U.: Relating hygroscopicity and composition of organic aerosol particulate matter, Atmos. Chem. Phys., 11, 1155–1165, http://dx.doi.org/10.5194/acp-11-1155-2011doi:10.5194/acp-11-1155-2011, 2011. Fitzgerald, J. W.: Dependence of supersaturation spectrum of CCN on aerosol size distribution and composition, J. Atmos. Sci., 30, 628–634, 1973. Flatau, P. J., Walko, R. L., and Cotton, W. R.: Polynomial fits to saturation vapor pressure, J. Appl. Meteorology, 31, 1507–1513, 1992. Fors, E. O., Swietlicki, E., Svenningsson, B., Kristensson, A., Frank, G. P., and Sporre, M.: Hygroscopic properties of the ambient aerosol in southern Sweden – a two year study, Atmos. Chem. Phys., 11, 8343–8361, http://dx.doi.org/10.5194/acp-11-8343-2011doi:10.5194/acp-11-8343-2011, 2011. Fredenslund, A., Jones, R. L., and Prausnitz, J. M.: Group-contribution estimation of activity coefficients in nonideal liquid mixtures, AIChE J., 21, 1086–1099, 1975. Gao, Y., Chen, B. C., and Yu, L. T.: Efflorescence relative humidity of airborne sodium chloride particles: A theoretical investigation, Atmos. Environ., 41, 2019–2023, 2007. Giebl, H., Berner, A., Reischl, G., Puxbaum, H., Kasper-Giebl, A., and Hitzenberger, R.: CCN activation of oxalic and malonic acid test aerosols with the University of Vienna cloud condensation nuclei counter, J. Aerosol Sci., 33, 1623–1634, http://dx.doi.org/10.1016/S0021-8502(02)00115-5doi:10.1016/S0021-8502(02)00115-5, 2002. Good, N., Topping, D. O., Allan, J. D., Flynn, M., Fuentes, E., Irwin, M., Williams, P. I., Coe, H., and McFiggans, G.: Consistency between parameterisations of aerosol hygroscopicity and CCN activity during the RHaMBLe discovery cruise, Atmos. Chem. Phys., 10, 3189–3203, http://dx.doi.org/10.5194/acp-10-3189-2010doi:10.5194/acp-10-3189-2010, 2010a. Good, N., Topping, D. O., Duplissy, J., Gysel, M., Meyer, N. K., Metzger, A., Turner, S. F., Baltensperger, U., Ristovski, Z., Weingartner, E., Coe, H., and McFiggans, G.: Widening the gap between measurement and modelling of secondary organic aerosol properties?, Atmos. Chem. Phys., 10, 2577–2593, http://dx.doi.org/10.5194/acp-10-2577-2010doi:10.5194/acp-10-2577-2010, 2010b. Gunthe, S. S., King, S. M., Rose, D., Chen, Q., Roldin, P., Farmer, D. K., Jimenez, J. L., Artaxo, P., Andreae, M. O., Martin, S. T., and Pöschl, U.: Cloud condensation nuclei in pristine tropical rainforest air of Amazonia: size-resolved measurements and modeling of atmospheric aerosol composition and CCN activity, Atmos. Chem. Phys., 9, 7551–7575, http://dx.doi.org/10.5194/acp-9-7551-2009doi:10.5194/acp-9-7551-2009, 2009. Gunthe, S. S., Rose, D., Su, H., Garland, R. M., Achtert, P., Nowak, A., Wiedensohler, A., Kuwata, M., Takegawa, N., Kondo, Y., Hu, M., Shao, M., Zhu, T., Andreae, M. O., and Pöschl, U.: Cloud condensation nuclei (CCN) from fresh and aged air pollution in the megacity region of Beijing, Atmos. Chem. Phys., 11, 11023–11039, http://dx.doi.org/10.5194/acp-11-11023-2011doi:10.5194/acp-11-11023-2011, 2011. Gysel, M., Weingartner, E., and Baltensperger, U.: Hygroscopicity of aerosol particles at low temperatures. 2. Theoretical and experimental hygroscopic properties of laboratory generated aerosols, Environ. Sci. Technol., 36, 63–68, http://dx.doi.org/10.1021/es010055gdoi:10.1021/es010055g, 2002. Gysel, M., Weingartner, E., Nyeki, S., Paulsen, D., Baltensperger, U., Galambos, I., and Kiss, G.: Hygroscopic properties of water-soluble matter and humic-like organics in atmospheric fine aerosol, Atmos. Chem. Phys., 4, 35–50, http://dx.doi.org/10.5194/acp-4-35-2004doi:10.5194/acp-4-35-2004, 2004. Hancock, B. C. and Parks, M.: What is the true solubility advantage for amorphous pharmaceuticals?, Pharm. Res., 17, 397–404, 2000. Hansen, H. K., Rasmussen, P., Fredenslund, A., Schiller, M., and Gmebling, J.: Vapor-liquid equilibria by UNIFAC group contribution. 5. Revision and extension, Ind. Eng. Chem. Res., 30, 2352–2355, 1991. Hatch, C. D., Gierlus, K. M. Schuttlefield, J. D., and Grassian V. H.: Water adsorption and cloud condensation nuclei activity of calcite and calcite coated with model humic and fulvic acids, Atmos. Environ., 42, 5672–5684, 2008. Huff Hartz, K. E., Rosenørn, T., Ferchak, S. R., Raymond, T. M., Bilde, M., Donahue, N. M., and Pandis, S. N.: Cloud condensation nuclei activation of monoterpene and sesquiterpene secondary organic aerosol, J. Geophys. Res., 110, D14208, http://dx.doi.org/10.1029/2004JD005754doi:10.1029/2004JD005754, 2005. Irwin, M., Good, N., Crosier, J., Choularton, T. W., and McFiggans, G.: Reconciliation of measurements of hygroscopic growth and critical supersaturation of aerosol particles in central Germany, Atmos. Chem. Phys., 10, 11737–11752, http://dx.doi.org/10.5194/acp-10-11737-2010doi:10.5194/acp-10-11737-2010, 2010. Junge, C. and McLaren, E.: Relationship of cloud nuclei spectra to aerosol size distribution and composition, J. Atmos. Sci., 28, 382–390, 1971. Khalizov, A. F, Zhang, R., Zhang, D., Xue, H., Pagels, J., and McMurry, P. H.: Formation of highly hygroscopic soot aerosols upon internal mixing with sulfuric acid vapor, J. Geophys. Res., 114, D05208, http://dx.doi.org/10.1029/2008JD010595doi:10.1029/2008JD010595, 2009. Kirgintsev, A. and Luk'yanov, A. V.: Isopiestic investigations of ternary solutions. VIII. General treatment of the results for 34 ternary aqueous salt solutions, Russian Journal of Physical Chemistry, 40, 953–956, 1966 Krämer, L., Pöschl, U., and Niessner, R.: Microstructural rearrangement of sodium chloride condensation aerosol particles on interaction with water vapor, J. Aerosol. Sci., 31, 673–685, http://dx.doi.org/10.1016/S0021-8502(99)00551-0doi:10.1016/S0021-8502(99)00551-0, 2000. Kreidenweis, S. M., Koehler, K., DeMott, P. J., Prenni, A. J., Carrico, C., and Ervens, B.: Water activity and activation diameters from hygroscopicity data – Part I: Theory and application to inorganic salts, Atmos. Chem. Phys., 5, 1357–1370, http://dx.doi.org/10.5194/acp-5-1357-2005doi:10.5194/acp-5-1357-2005, 2005. Kreidenweis, S. M., Petters, M. D., and DeMott, P. J.: Single-parameter estimates of aerosol water content, Environ. Res. Lett., 3, 035002, http://dx.doi.org/10.1088/1748-9326/3/3/035002doi:10.1088/1748-9326/3/3/035002, 2008. Kuhlbusch, T. A. J., Hertlein, A.-M., and Schütz, L. W.: Sources, determination, monitoring, and transport of carbonaceous aerosols in Mainz, Germany, Atmos. Environ., 32, 1097–1110, 1998. Kulmala, M., Laaksonen, A., Charlson, R. J., and Korhonen, P.: Clouds without supersaturation, Nature, 388, 336–337, 1997. Laaksonen, A., Korhonen, P., Kulmala, M., and Charlson, R. J. :Modification of the Köhler equation to include soluble trace gases and slightly soluble substances, J. Atmos. Sci., 55, 853–862, 1998. Lee, C. T. and Hsu, W. C.: The measurement of liquid water mass associated with collected hygroscopic particles, Aerosol Sci., 31, 189–197, 2000. Ling, T. Y. and Chan, C. K.: Partial crystallization and deliquescence of particles containing ammonium sulfate and dicarboxylic acids, J. Geophys. Res., 113, D14205, http://dx.doi.org/10.1029/2008JD009779doi:10.1029/2008JD009779, 2008. Marcolli, C. and Krieger, U. K..: Phase changes during hygroscopic cycles of mixed organic/inorganic model systems of tropospheric aerosols, J. Phys. Chem. A., 110, 1881–1893, http://dx.doi.org/10.1021/jp0556759doi:10.1021/jp0556759, 2006. Marcolli, C., Luo, B., and Peter, T.: Mixing of the organic aerosol fractions: Liquids as the thermodynamically stable phases, J. Phys. Chem. A., 108, 2216–2224, http://dx.doi.org/10.1021/jp036080ldoi:10.1021/jp036080l, 2004. Martin, S. T.: Phase transitions of aqueous atmospheric particles, Chem. Rev., 100, 3403–3453, http://dx.doi.org/10.1021/cr990034tdoi:10.1021/cr990034t, 2000. Martin, S. T., Andreae, M. O., Althausen, D., Artaxo, P., Baars, H., Borrmann, S., Chen, Q., Farmer, D. K., Guenther, A., Gunthe, S. S., Jimenez, J. L., Karl, T., Longo, K., Manzi, A., Müller, T., Pauliquevis, T., Petters, M. D., Prenni, A. J., Pöschl, U., Rizzo, L. V., Schneider, J., Smith, J. N., Swietlicki, E., Tota, J., Wang, J., Wiedensohler, A., and Zorn, S. R.: An overview of the Amazonian Aerosol Characterization Experiment 2008 (AMAZE-08), Atmos. Chem. Phys., 10, 11415–11438, http://dx.doi.org/10.5194/acp-10-11415-2010doi:10.5194/acp-10-11415-2010, 2010. Mayol-Bracero, O. L., Guyon, P., Graham, B., Roberts, G., and Andreae, M. O.: Water-soluble organic compounds in biomass burning aerosols over Amazonia. 2. Apportionment of the chemical composition and importance of the polyacidic fraction, J. Geophys. Res., 107, 8091, http://dx.doi.org/10.1029/2001JD000522doi:10.1029/2001JD000522, 2002. McFiggans, G., Artaxo, P., Baltensperger, U., Coe, H., Facchini, M. C., Feingold, G., Fuzzi, S., Gysel, M., Laaksonen, A., Lohmann, U., Mentel, T. F., Murphy, D. M., O'Dowd, C. D., Snider, J. R., and Weingartner, E.: The effect of physical and chemical aerosol properties on warm cloud droplet activation, Atmos. Chem. Phys., 6, 2593–2649, http://dx.doi.org/10.5194/acp-6-2593-2006doi:10.5194/acp-6-2593-2006, 2006. McGlashan, M. L.: Deviations from Raoult's law, J. Chem. Educ., 40, 516–518, 1963. Metzger, S., Steil, B., Xu, L., Penner, J. E., and Lelieveld, J.: New representation of water activity based on a single solute specific constant to parameterize the hygroscopic growth of aerosols in atmospheric models, Atmos. Chem. Phys., 12, 5429–5446, http://dx.doi.org/10.5194/acp-12-5429-2012doi:10.5194/acp-12-5429-2012, 2012. Mikhailov, E., Vlasenko, S., Niessner, R., and Pöschl, U.: Interaction of aerosol particles composed of protein and saltswith water vapor: hygroscopic growth and microstructural rearrangement, Atmos. Chem. Phys., 4, 323–350, http://dx.doi.org/10.5194/acp-4-323-2004doi:10.5194/acp-4-323-2004, 2004. Mikhailov, E., Vlasenko, S., Martin, S. T., Koop, T., and Pöschl, U.: Amorphous and crystalline aerosol particles interacting with water vapor: conceptual framework and experimental evidence for restructuring, phase transitions and kinetic limitations, Atmos. Chem. Phys., 9, 9491–9522, http://dx.doi.org/10.5194/acp-9-9491-2009doi:10.5194/acp-9-9491-2009, 2009. Mikhailov, E. F., Merkulov, V. V., Vlasenko, S. S., and Pöschl, U.: Filter-based differential hygroscopicity analyzer, Izvestya Atmospheric and Oceanic Physics, 47, 747–759, 2011. Mitchell, R. I. and Pilcher, J. M.: Improved cascade impactor for measuring aerosol particle sizes, Industrial and Engineering Chemistry, 51, 1039–1042, 1959. Mochida, M., Kuwata, M., Miyakawa, T., Takegawa, N., Kawamura, K., and Kondo, Y.: Relationship between hygroscopicity and cloud condensation nuclei activity for urban aerosols in Tokyo, J. Geophys. Res., 111, D23204, http://dx.doi.org/10.1029/2005JD006980doi:10.1029/2005JD006980, 2006. Mosharraf, M. and Nyström, C.: The effect of dry mixing on the apparent solubility of hydrophobic, sparingly soluble drugs, Europ. J. Pharm. Sci., 9, 145–156, 1999. Murdande, S. B., Pikal, M. J., Shanker, R. M., and Bogner, R. H.: Solubility advantage of amorphous pharmaceuticals, II. Application of quantitative thermodynamic relationships for prediction of solubility enhancement in structurally diverse insoluble pharmaceuticals, Pharm. Res., 27, 2704–2714, 2010. Murdande, S. B., Pikal, M. J., Shanker, R. M., and Bogner, R. H.: Aqueous solubility of crystalline and amorphous drugs: challenges in measurement, Pharm. Develop. Technol., 16, 187–200, 2011. Peng, C., Chan M. N., and Chan, C. K.: The hygroscopic properties of dicarboxylic and multifunctional acids: Measurements and UNIFAC predictions, Environ. Sci. Technol., 35, 4495–4501, 2001. Petters, M. D. and Kreidenweis, S. M.: A single parameter representation of hygroscopic growth and cloud condensation nucleus activity, Atmos. Chem. Phys., 7, 1961–1971, http://dx.doi.org/10.5194/acp-7-1961-2007doi:10.5194/acp-7-1961-2007, 2007. Petters, M. D. and Kreidenweis, S. M.: A single parameter representation of hygroscopic growth and cloud condensation nucleus activity – Part 2: Including solubility, Atmos. Chem. Phys., 8, 6273–6279, http://dx.doi.org/10.5194/acp-8-6273-2008doi:10.5194/acp-8-6273-2008, 2008. Petters, M. D., Carrico, C. M., Kreidenweis, S. M., Prenni, A. J., DeMott, P. J., Collett, J. L., and Moosmüller, H.: Cloud condensation nucleation activity of biomass burning aerosol, J. Geophys. Res., 114, D22205, http://dx.doi.org/10.1029/2009JD012353doi:10.1029/2009JD012353, 2009. Pöschl, U., Martin, S. T., Sinha, B., Chen, Q., Gunthe, S. S., Huffman, J. A., Borrmann, S., Farmer, D. K., Garland, R. M., Helas, G., Jimenez, J.L., King, S. M., Manzi, A., Mikhailov, E., Pauliquevis, T., Petters, M. D., Prenni, A. J., Roldin, P., Rose, D., Schneider, J., Su, H., Zorn, S. R., Artaxo, P., and Andreae, M. O.: Rainforest Aerosols as Biogenic Nuclei of Clouds and Precipitation in the Amazon, Science, 329, 1513–1516, http://dx.doi.org/10.1126/science.1191056doi:10.1126/science.1191056, 2010. Pringle, K. J., Tost, H., Pozzer, A., Pöschl, U., and Lelieveld, J.: Global distribution of the effective aerosol hygroscopicity parameter for CCN activation, Atmos. Chem. Phys., 10, 5241–5255, http://dx.doi.org/10.5194/acp-10-5241-2010doi:10.5194/acp-10-5241-2010, 2010. Pruppacher, H. R. and Klett, J. D.: Microphysics of clouds and precipitation, Kluwer Academic Publishers, Dordrecht, 2000. Raymond T. M. and Pandis S. N.: Cloud activation of single-component organic aerosol particles, J. Geophys. Res., 107, 4787, http://dx.doi.org/10.1029/2002JD002159doi:10.1029/2002JD002159, 2002. Raymond, T. M. and Pandis, S. N.: Formation of cloud droplets by multicomponent organic particles, J. Geophys. Res., 108, 4469, http://dx.doi.org/10.1029/2003JD003503doi:10.1029/2003JD003503, 2003. Rissler, J., Swietlicki, E., Zhou, J., Roberts, G., Andreae, M. O., Gatti, L. V., and Artaxo, P.: Physical properties of the sub-micrometer aerosol over the Amazon rain forest during the wet-to-dry season transition – comparison of modeled and measured CCN concentrations, Atmos. Chem. Phys., 4, 2119–2143, http://dx.doi.org/10.5194/acp-4-2119-2004doi:10.5194/acp-4-2119-2004, 2004. Roberts, G. C., Day, D. A., Russell, L. M., Dunlea, E. J., Jimenez, J. L., Tomlinson, J. M., Collins, D. R., Shinozuka, Y., and Clarke, A. D.: Characterization of particle cloud droplet activity and composition in the free troposphere and the boundary layer during INTEX-B, Atmos. Chem. Phys., 10, 6627–6644, http://dx.doi.org/10.5194/acp-10-6627-2010doi:10.5194/acp-10-6627-2010, 2010. Rose, D., Gunthe, S. S., Mikhailov, E., Frank, G. P., Dusek, U., Andreae, M. O., and Pöschl, U.: Calibration and measurement uncertainties of a continuous-flow cloud condensation nuclei counter (DMT-CCNC): CCN activation of ammonium sulfate and sodium chloride aerosol particles in theory and experiment, Atmos. Chem. Phys., 8, 1153–1179, http://dx.doi.org/10.5194/acp-8-1153-2008doi:10.5194/acp-8-1153-2008, 2008. Rose, D., Nowak, A., Achtert, P., Wiedensohler, A., Hu, M., Shao, M., Zhang, Y., Andreae, M. O., and Pöschl, U.: Cloud condensation nuclei in polluted air and biomass burning smoke near the mega-city Guangzhou, China – Part 1: Size-resolved measurements and implications for the modeling of aerosol particle hygroscopicity and CCN activity, Atmos. Chem. Phys., 10, 3365–3383, http://dx.doi.org/10.5194/acp-10-3365-2010doi:10.5194/acp-10-3365-2010, 2010. Rose, D., Gunthe, S. S., Su, H., Garland, R. M., Yang, H., Berghof, M., Cheng, Y. F., Wehner, B., Achtert, P., Nowak, A., Wiedensohler, A., Takegawa, N., Kondo, Y., Hu, M., Zhang, Y., Andreae, M. O., and Pöschl, U.: Cloud condensation nuclei in polluted air and biomass burning smoke near the mega-city Guangzhou, China – Part 2: Size-resolved aerosol chemical composition, diurnal cycles, and externally mixed weakly CCN-active soot particles, Atmos. Chem. Phys., 11, 2817–2836, http://dx.doi.org/10.5194/acp-11-2817-2011doi:10.5194/acp-11-2817-2011, 2011. Seinfeld, J. H. and Pandis, S. N.: Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, John Wiley and Sons, Inc., New York, 2006. Setschenov, J.: Über die Konstitution der Salzlösungen aufgrund ihres Verhaltens zu Kohlensäure, Z. Phys. Chem., 4, 117–125, 1889. Shulman, M. L., Jacobson, M. C., Carlson, R. J., Synovec, R. E., and Young, T. E.: Dissolution behavior and surface tension effects of organic compounds in nucleating cloud droplets, Geophys. Res. Lett., 23, 277–280, http://dx.doi.org/10.1029/95GL03810doi:10.1029/95GL03810, 1996. Sjogren, S., Gysel, M., Weingartner, E., Baltensperger, U., Cubison, M. J., Coe, H., Zardini, A. A., Marcolli, C., Krieger, U. R., and Peter, T.: Hygroscopic growth and water uptake kinetics of two-phase aerosol particles consisting of ammonium sulphate, adipic and humic acid mixtures, J. Aerosol Sci., 38, 157–171, 2007. Speer, R. E., Edney, E. O., and Kleindenst, T. E.: Impact of organic compounds on the concentrations of liquid water in ambient PM2:5, Aerosol Sci., 34, 63–77, 2003. Stephen, H. and Stephen, T. (Eds.): Solubilities of inorganic and organic compounds, Pergamon Press, Oxford, 1963. Stokes, R. H. and Robinson, R. A.: Interactions in aqueous nonelectrolyte solutions: I. Solute-solvent equilibria, J. Phys. Chem., 70, 2126–2130, 1966. Sullivan, R. C., Moore, M. J. K., Petters, M. D., Kreidenweis, S. M., Roberts, G. C., and Prather, K. A.: Effect of chemical mixing state on the hygroscopicity and cloud nucleation properties of calcium mineral dust particles, Atmos. Chem. Phys., 9, 3303–3316, http://dx.doi.org/10.5194/acp-9-3303-2009doi:10.5194/acp-9-3303-2009, 2009. Svenningsson, B., Rissler, J., Swietlicki, E., Mircea, M., Bilde, M., Facchini, M. C., Decesari, S., Fuzzi, S., Zhou, J., Mønster, J., and Rosenørn, T.: Hygroscopic growth and critical supersaturations for mixed aerosol particles of inorganic and organic compounds of atmospheric relevance, Atmos. Chem. Phys., 6, 1937–1952, http://dx.doi.org/10.5194/acp-6-1937-2006doi:10.5194/acp-6-1937-2006, 2006. Tang, I. N. and Munkelwitz, H. R.: Composition and temperature dependence of the deliquescence properties of hygroscopic aerosol, Atmos. Environ., 27A, 467–473, http://dx.doi.org/10.1016/0960-1686(93)90204-Cdoi:10.1016/0960-1686(93)90204-C, 1993. Tang, I. N. and Munkelwitz, H. R.: Water activities, densities, and refractive indices of aqueous sulfates and sodium nitrate droplets of atmospheric importance, J. Geophys. Res., 20, 18801–18808, 1994. Tong, C., Clegg, L. C., and Seinfeld, J. H.: Comparison of activity coefficient models for atmospheric aerosols containing mixtures of electrolytes, organics, and water, Atmos. Environ., 42, 5459–5482, 2008. Topping, D. O., McFiggans, G. B., and Coe, H.: A curved multi-component aerosol hygroscopicity model framework: Part 1 – Inorganic compounds, Atmos. Chem. Phys., 5, 1205–1222, http://dx.doi.org/10.5194/acp-5-1205-2005doi:10.5194/acp-5-1205-2005, 2005a. Topping, D. O., McFiggans, G. B., and Coe, H.: A curved multi-component aerosol hygroscopicity model framework: Part 2 – Including organic compounds, Atmos. Chem. Phys., 5, 1223–1242, http://dx.doi.org/10.5194/acp-5-1223-2005doi:10.5194/acp-5-1223-2005, 2005b. Virtanen, A., Rönkkö, T., Kannosto, J., Ristimäki, J., Mäkelä, J. M., Keskinen, J., Pakkanen, T., Hillamo, R., Pirjola, L., and Hämeri, K.: Winter and summer time size distributions and densities of traffic-related aerosol particles at a busy highway in Helsinki, Atmos. Chem. Phys., 6, 2411–2421, http://dx.doi.org/10.5194/acp-6-2411-2006doi:10.5194/acp-6-2411-2006, 2006. Wang, Z., King, S. M., Freney, E., Rosenoern, T., Smith, M. L., Chen, Q., Kuwata, M., Lewis, E. R., Pöschl, U., Wang, W., Buseck, P. R., and Martin, S. T.: The Dynamic Shape Factor of Sodium Chloride Nanoparticles as Regulated by Drying Rate, Aerosol Sci. Technol., 44, 939–953, http://dx.doi.org/10.1080/02786826.2010.503204doi:10.1080/02786826.2010.503204, 2010. Wex, H., Stratmann, F., Hennig, T., Hartmann, S., Niedermeier, D., Nilsson, E., Ocskay, R., Rose, D., Salma, I., and Ziese, M.: Connecting hygroscopic growth at high humidities to cloud activation for different particle types, Environ. Res. Lett., 3, 1–10, http://dx.doi.org/10.1088/1748-9326/3/3/035004doi:10.1088/1748-9326/3/3/035004, 2008. Wexler, A. S. and Clegg, S. L.: Atmospheric aerosol models for systems including the ions H$^+$, NH$_4+$, Na$^+$, SO$_4^2-$, NO$_3^-$, Cl$^-$, Br$^-$, and H<sub>2</sub>O, J. Geophys. Res., 107, ACH 14-1–ACH 14-14, http://dx.doi.org/10.1029/2001JD000451doi:10.1029/2001JD000451, 2002. Wexler, A. S. and Seinfeld, J. H.: Second-generation inorganic aerosol model, Atmos. Environ., 25A, 2731–2748, http://dx.doi.org/10.1016/0960-1686(91)90203-Jdoi:10.1016/0960-1686(91)90203-J, 1991. Yeung, M. C. and Chan, C. K.: Water content and phase transitions in particles of inorganic and organic species and their mixtures using micro-Raman spectroscopy, Aerosol Sci. Technol., 44, 269–280, 2010. Yeung, M. C., Lee, A. K. Y., and Chan, C. K.: Phase transition and hygroscopic properties of internally mixed ammonium sulfate and adipic acid (AS-AA) particles by optical microscopic imaging and Raman spectroscopy, Aerosol Sci. Technol., 43, 387–399, 2009. Zardini, A. A., Sjogren, S., Marcolli, C., Krieger, U. K., Gysel, M., Weingartner, E., Baltensperger, U., and Peter, T.: A combined particle trap/HTDMA hygroscopicity study of mixed inorganic/organic aerosol particles, Atmos. Chem. Phys., 8, 5589–5601, http://dx.doi.org/10.5194/acp-8-5589-2008doi:10.5194/acp-8-5589-2008, 2008. Zuend, A., Marcolli, C., Luo, B. P., and Peter, T.: A thermodynamic model of mixed organic-inorganic aerosols to predict activity coefficients, Atmos. Chem. Phys., 8, 4559–4593, http://dx.doi.org/10.5194/acp-8-4559-2008doi:10.5194/acp-8-4559-2008, 2008. Zuend, A., Marcolli, C., Booth, A. M., Lienhard, D. M., Soonsin, V., Krieger, U. K., Topping, D. O., McFiggans, G., Peter, T., and Seinfeld, J. H.: 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, Atmos. Chem. Phys., 11, 9155–9206, http://dx.doi.org/10.5194/acp-11-9155-2011doi:10.5194/acp-11-9155-2011, 2011.