ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-7267-2010 The importance of aerosol mixing state and size-resolved composition on CCN concentration and the variation of the importance with atmospheric aging of aerosols Wang J. 1 Cubison M. J. 2 Aiken A. C. 2 Jimenez J. L. 2 Collins D. R. 3 Atmospheric Sciences Division, Brookhaven National Laboratory, Upton, NY, USA Department of Chemistry and Biochemistry, and CIRES, University of Colorado, Boulder, CO, USA Department of Atmospheric Sciences, Texas A&M University, College Station, TX, USA 06 08 2010 10 15 7267 7283 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/10/7267/2010/acp-10-7267-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/7267/2010/acp-10-7267-2010.pdf

Aerosol microphysics, chemical composition, and CCN concentrations were measured at the T0 urban supersite in Mexico City during Megacity Initiative: Local and Global Research Observations (MILAGRO) in March 2006. The aerosol size distribution and composition often showed strong diurnal variation associated with traffic emissions and aging of aerosols through coagulation and local photochemical production of secondary aerosol species. CCN concentrations (<i>N</i><sub>CCN</sub>) are derived using Köhler theory from the measured aerosol size distribution and various simplified aerosol mixing state and chemical composition, and are compared to concurrent measurements at five supersaturations ranging from 0.11% to 0.35%. The influence of assumed mixing state on calculated <i>N</i><sub>CCN</sub> is examined using both aerosols observed during MILAGRO and representative aerosol types. The results indicate that while ambient aerosols often consist of particles with a wide range of compositions at a given size, <i>N</i><sub>CCN</sub> may be derived within ~20% assuming an internal mixture (i.e., particles at a given size are mixtures of all participating species, and have the identical composition) if great majority of particles has an overall κ (hygroscopicity parameter) value greater than 0.1. For a non-hygroscopic particle with a diameter of 100 nm, a 3 nm coating of sulfate or nitrate is sufficient to increase its κ from 0 to 0.1. The measurements during MILAGRO suggest that the mixing of non-hygroscopic primary organic aerosol (POA) and black carbon (BC) particles with photochemically produced hygroscopic species and thereby the increase of their κ to 0.1 take place in a few hours during daytime. This rapid process suggests that during daytime, a few tens of kilometers away for POA and BC sources, <i>N</i><sub>CCN</sub> may be derived with sufficient accuracy by assuming an internal mixture, and using bulk chemical composition. The rapid mixing also indicates that, at least for very active photochemical environments such as Mexico City, the timescale during daytime for the conversion of hydrophobic POA and BC to hydrophilic particles is substantially shorter than the 1–2 days used in some global models. The conversion time scale is substantially longer during night. Most POA and BC particles emitted during evening hours likely remain non-hygroscopic until efficiently internally mixed with secondary species in the next morning. The results also suggest that the assumed mixing state strongly impacts calculated <i>N</i><sub>CCN</sub> only when POA and BC represent a large fraction of the total aerosol volume. One of the implications is that while physically unrealistic, external mixtures, which are used in many global models, may also sufficiently predict <i>N</i><sub>CCN</sub> for aged aerosol, as the contribution of non-hygroscopic POA and BC to overall aerosol volume is often substantially reduced due to the condensation of secondary species.

 References Aggarwal, S. G. and Kawamura, K.: Carbonaceous and inorganic composition in long-range transported aerosols over northern Japan: Implication for aging of water-soluble organic fraction, Atmos. Environ., 43, 2532–2540, 2009. Aiken,A. C., DeCarlo, P. F., Kroll, J. H., et al.: O/C and OM/OC Ratios of Primary, Secondary, and Ambient Organic Aerosols with High Resolution Time-of-Flight Aerosol Mass Spectrometry Environ. Sci. Technol., 42, 4478–4485, 2008. Aiken, A. C., Salcedo, D., Cubison, M. J., Huffman, J. A., DeCarlo, P. F., Ulbrich, I. M., Docherty, K. S., Sueper, D., Kimmel, J. R., Worsnop, D. R., Trimborn, A., Northway, M., Stone, E. A., Schauer, J. J., Volkamer, R. M., Fortner, E., de Foy, B., Wang, J., Laskin, A., Shutthanandan, V., Zheng, J., Zhang, R., Gaffney, J., Marley, N. A., Paredes-Miranda, G., Arnott, W. P., Molina, L. T., Sosa, G., and Jimenez, J. L.: Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) - Part 1: Fine particle composition and organic source apportionment, Atmos. Chem. Phys., 9, 6633–6653, doi:10.5194/acp-9-6633-2009, 2009. Aiken, A. C., de Foy, B., Wiedinmyer, C., et al.: Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 2: Analysis of the biomass burning contribution and the modern carbon fraction, Atmos. Chem. Phys., 10, 5315–5341, 2010. Albrecht, B. A.: Aerosols, cloud microphysics, and fractional cloudiness, Science, 245, 1227–1230, 1989. Andreae, M. O. and Rosenfeld, D.: Aerosol-cloud-precipitation interactions. Part 1. The nature and sources of cloud-active aerosols, Earth Sci. Rev., 89, 13–41, 2008. Asa-Awuku, A., Engelhart, G. J., Lee, B. H., Pandis, S. N., and Nenes, A.: Relating CCN activity, volatility, and droplet growth kinetics of beta-caryophyllene secondary organic aerosol, Atmos. Chem. Phys., 9, 795–812, doi:10.5194/acp-9-795-2009, 2009. Bergin, M. H., Schwartz, S. E., Halthore, R. N., et al.: Comparison of aerosol optical depth inferred from surface measurements with that determined by Sun photometry for cloud-free conditions at a continental US site, J. Geophys. Res., 105, 6807–6816, 2000. 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. Broekhuizen, K., Chang, R. Y. W., Leaitch, W. R., Li, S. M., and Abbatt, J. P. D.: Closure between measured and modeled cloud condensation nuclei (CCN) using size-resolved aerosol compositions in downtown Toronto, Atmos. Chem. Phys., 6, 2513–2524, doi:10.5194/acp-6-2513-2006, 2006. Canagaratna, M. R., Jayne, J. T., Jimenez, J. L., et al.: Chemical and Microphysical Characterization of Ambient Aerosols with the Aerodyne Aerosol Mass Spectrometer, Mass Spec. Rev., 26, 185–222, 2007. Cantrell, W., Shaw, G., Cass, G. R., et al.: Closure between aerosol particles and cloud condensation nuclei at Kaashidhoo Climate Observatory, J. Geophys. Res., 106, 28711–28718, 2001. Cappa, C. D. and Jimenez, J. L.: Quantitative estimates of the volatility of ambient organic aerosol, Atmos. Chem. Phys., 10, 5409–5424, doi:10.5194/acp-10-5409-2010, 2010. Carrico, C. M., Petters, M. D., Kreidenweis, S. M., et al.: Aerosol hygroscopicity and cloud droplet activation of extracts of filters from biomass burning experiments, J. Geophys. Res., 113, D08206, doi: 10.1029/2007JD009274, 2008. Chang, R. Y. W., Liu, P. S. K., Leaitch, W. R., and Abbatt, J. P. D.: Comparison between measured and predicted CCN concentrations at Egbert, Ontario: Focus on the organic aerosol fraction at a semi-rural site, Atmos. Environ., 41, 8172–8182, 2007. Chung, S. H. and Seinfeld, J. H.: Global distribution and climate forcing of carbonaceous aerosols, J. Geophys. Res., 107, 4407, doi:10.1029/2001JD001397, 2002. Clegg, S. L., Brimblecombe, P., and Wexler, A. S.: Thermodynamic model of the system H$^+$-NH$_4^+$-Na$^+$-SO$_4^2-$-NB$_3-$-Cl$^-$-H<sub>2</sub>O at 298.15 K, J. Phys. Chem. A, 102, 2155–2171, 1998. Collins, D. R., Flagan, R. C., and Seinfeld, J. H.: Improved inversion of scanning DMA data, Aerosol Sci. Technol., 36, 1–9, 2002. Conant, W. C., VanReken, T. M., Rissman, T. A., et al.: Aerosol-Cloud Drop Concentration Closure in Warm Cumulus. J. Geophys. Res., 109, D13204, doi:10.1029/2003JD004324, 2004. Cross, E. S., Slowik, J. G., Davidovits, P., et al.: Laboratory and ambient particle density determinations using light scattering in conjunction with aerosol mass spectrometry, Aerosol Sci. Tech., 41, 343–359, 2007. Cross, E. S., Onasch, T. B., Canagaratna, M., Jayne, J. T., Kimmel, J., Yu, X.-Y., Alexander, M. L., Worsnop, D. R., and Davidovits, P.: Single particle characterization using a light scattering module coupled to a time-of-flight aerosol mass spectrometer, Atmos. Chem. Phys., 9, 7769–7793, doi:10.5194/acp-9-7769-2009, 2009. Cubison, M. J., Ervens, B., Feingold, G., Docherty, K. S., Ulbrich, I. M., Shields, L., Prather, K., Hering, S., and Jimenez, J. L.: The influence of chemical composition and mixing state of Los Angeles urban aerosol on CCN number and cloud properties, Atmos. Chem. Phys., 8, 5649–5667, doi:10.5194/acp-8-5649-2008, 2008. DeCarlo, P., Slowik, J. G., Worsnop, D. R., et al.: Particle Morphology and Density Characterization by Combined Mobility and Aerodynamic Diameter Measurements. Part 1: Theory. Aerosol Sci. Technol., 38, 1185–1205, 2004. DeCarlo, P. F., Kimmel, J. R., Trimborn, A., et al.: Field-Deployable, High-Resolution, Time-of-Flight Aerosol Mass Spectrometer, Anal. Chem., 78, 8281–8289, 2006. de Gouw, J. and Jimenez, J. L.: Organic Aerosols in the Earth's Atmosphere. Environ. Sci. Technol., 43, 7614–7618, 2009. Dusek, U., Frank, G. P., Hildebrandt, L., et al.: Size matters more than chemistry for cloud-nucleating ability of aerosol particles, Science, 312, 1375–1378, 2006. Dzepina, K., Volkamer, R. M., Madronich, S., Tulet, P., Ulbrich, I. M., Zhang, Q., Cappa, C. D., Ziemann, P. J., and Jimenez, J. L.: Evaluation of Recently-Proposed Secondary Organic Aerosol Models for a Case Study in Mexico City, Atmos. Chem. Phys., 9, 5681–5709, doi:10.5194/acp-9-5681-2009, 2009. Easter, R. C., Ghan, S. J., Zhang, Y., et al.: MIRAGE: Model description and evaluation of aerosols and trace gases, J. Geophys. Res., 109, D20210, doi:10.1029/2004JD004571, 2004. Ervens, B., Cubison, M., Andrews, E., et al.: Prediction of cloud condensation nucleus number concentration using measurements of aerosol size distributions and composition and light scattering enhancement due to humidity, J. Geophys. Res., 112, D10S32, doi:10.1029/2006JD007426, 2007. Ervens, B., Cubison, M. J., Andrews, E., Feingold, G., Ogren, J. A., Jimenez, J. L., Quinn, P. K., Bates, T. S., Wang, J., Zhang, Q., Coe, H., Flynn, M., and Allan, J. D.: CCN predictions using simplified assumptions of organic aerosol composition and mixing state: a synthesis from six different locations, Atmos. Chem. Phys., 10, 4795–4807, doi:10.5194/acp-10-4795-2010, 2010. Facchini, M. C., Mircea, M., Fuzzi, S., and Charlson, R. J.: Cloud albedo enhancement by surface-active organic solutes in growing droplets, Nature, 401, 257–259, 1999. Gasparini, R., Li, R. J., and Collins, D. R.: Integration of size distributions and size-resolved hygroscopicity measured during the Houston Supersite for compositional categorization of the aerosol, Atmos. Environ., 38, 3285–3303, 2004. Gasparini, R., Li, R. J., Collins, D. R., et al.: Application of aerosol hygroscopicity measured at the Atmospheric Radiation Measurement Program's Southern Great Plains site to examine composition and evolution, J. Geophys. Res., 111, D05S12, doi:10.1029/2004JD005448, 2006. Gong, S. L., Barrie, L. A., Blanchet, J. P., et al.: Canadian Aerosol Module: A size-segregated simulation of atmospheric aerosol processes for climate and air quality models – 1. Module development, J. Geophys. Res., 108, 4007, doi:10.1029/2001JD002002, 2003. 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 Poschl, 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, doi:10.5194/acp-9-7551-2009, 2009. Huff-Hartz, K. E. H., Tischuk, J. E., Chan, M. N., et al.: Cloud condensation nuclei activation of limited solubility organic aerosol, Atmos. Environ., 40, 605–617, 2006. Huffman, J. A., Docherty, K. S., Aiken, A. C., et al: Chemically-resolved aerosol volatility measurements from two megacity field studies, Atmos. Chem. Phys., 9, 7161–7182, doi:10.5194/acp-9-7161-2009, 2009. Intergovernmental panel on Climate Change (IPCC): Climate change 2007: The physical science basis, Cambridge University Press, New York, USA, 2007. Jimenez, J. L., Canagaratna, M. R., Donahue, et al.: Evolution of Organic Aerosols in the Atmosphere, Science, 326, 1525–1529, 2009. Johnson, K. S., Zuberi, B., Molina, L. T., Molina, M. J., Iedema, M. J., Cowin, J. P., Gaspar, D. J., Wang, C., and Laskin, A.: Processing of soot in an urban environment: case study from the Mexico City Metropolitan Area, Atmos. Chem. Phys., 5, 3033–3043, doi:10.5194/acp-5-3033-2005, 2005. Kanakidou, M., Seinfeld, J. H., Pandis, S. N., Barnes, I., Dentener, F. J., Facchini, M. C., Van Dingenen, R., Ervens, B., Nenes, A., Nielsen, C. J., Swietlicki, E., Putaud, J. P., Balkanski, Y., Fuzzi, S., Horth, J., Moortgat, G. K., Winterhalter, R., Myhre, C. E. L., Tsigaridis, K., Vignati, E., Stephanou, E. G., and Wilson, J.: Organic aerosol and global climatemodelling: a review, Atmos. Chem. Phys., 5, 1053–1123, doi:10.5194/acp-5-1053-2005, 2005. King, S. M., Rosenoern, T., Shilling, J. E., et al.: Cloud condensation nucleus activity of secondary organic aerosol particles mixed with sulfate, Geophys. Res. Lett., 34, L24806, doi: 10.1029/2007GL030390, 2007. King, S. M., Rosenoern, T., Shilling, J. E., Chen, Q., and Martin, S. T.: Increased cloud activation potential of secondary organic aerosol for atmospheric mass loadings, Atmos. Chem. Phys., 9, 2959–2971, doi:10.5194/acp-9-2959-2009, 2009. Köhler, H.: The nucleus in and the growth of hygroscopic droplets, Trans. Farad. Soc., 32, 1152–1161, 1936. Liu, P. S. K., Leaitch, W. R., Banic, C. M., et al.: Aerosol observations at Chebogue Point during the 1993 North Atlantic Regional Experiment: Relationships among cloud condensation nuclei, size distribution, and chemistry, J. Geophys. Res., 101, 28971–28990, 1996. Malloy, Q. G. J., Nakao, S., Qi, L., et al.: Real-Time Aerosol Density Determination Utilizing a Modified Scanning Mobility Particle SizerAerosol Particle Mass Analyzer System, Aerosol Sci. Tech., 43, 673–678, 2009. Marley, N. A., Gaffney, J. S., Castro, T., Salcido, A., and Frederick, J.: Measurements of aerosol absorption and scattering in the Mexico City Metropolitan Area during the MILAGRO field campaign: a comparison of results from the T0 and T1 sites, Atmos. Chem. Phys., 9, 189-206, 2009. Medina, J., Nenes, A., Sotiropoulou, R. E. P., et al.: Cloud condensation nuclei closure during the International Consortium for Atmospheric Research on Transport and Transformation 2004 campaign: Effects of size-resolved composition, J. Geophys. Res., 112, D10S31, doi:10.1029/2006JD007588, 2007. Ming, Y., Ramaswamy, V., Donner, L. J., et al.: Modeling the interactions between aerosols and liquid water clouds with a self-consistent cloud scheme in a general circulation model, J. Atmos. Sci., 64, 1189–1209, 2007. Mircea, M., Facchini, M. C., Decesari, S., Cavalli, F., Emblico, L., Fuzzi, S., Vestin, A., Rissler, J., Swietlicki, E., Frank, G., Andreae, M. O., Maenhaut, W., Rudich, Y., and Artaxo, P.: Importance of the organic aerosol fraction for modeling aerosol hygroscopic growth and activation: a case study in the Amazon Basin, Atmos. Chem. Phys., 5, 3111–3126, doi:10.5194/acp-5-3111-2005, 2005. Mochida, M., Kuwata, M., Miyakawa, T., et al.: Relationship between hygroscopicity and cloud condensation nuclei activity for urban aerosols in Tokyo, J. Geophys. Res., 111, D23204,, doi:10.1029/2005JD006980, 2006. Moffet, R. C., de Foy, B., Molina, L. T., Molina, M. J., and Prather, K. A.: Measurement of ambient aerosols in northern Mexico City by single particle mass spectrometry, Atmos. Chem. Phys., 8, 4499–4516, doi:10.5194/acp-8-4499-2008, 2008. Moffet, R. C. and Prather, K. A.: In-situ measurements of the mixing state and optical properties of soot with implications for radiative forcing estimates, Proc. Natl. Acad. Sci. USA, 106, 11872–11877, 2009. Molina, L. T., Madronich, S., Gaffney, J. S., Apel, E., de Foy, B., Fast, J., Ferrare, R., Herndon, S., Jimenez, J. L., Lamb, B., Osornio-Vargas, A. R., Russell, P., Schauer, J. J., Stevens, P. S., and Zavala, M.: An overview of the MILAGRO 2006 campaign: Mexico City emissions and their transport and transformation, Atmos. Chem. Phys. Discuss., 10, 7819–7983, doi:10.5194/acpd-10-7819-2010, 2010. Moteki, N., Kondo, Y., Miyazaki, Y., et al.: Evolution of mixing state of black carbon particles: Aircraft measurements over the western Pacific in March 2004, Geophys. Res. Lett., 34, L11803, doi: 10.1029/2006GL028943, 2007. Murphy, D. M., Cziczo, D. J., Froyd, K. D., et al., Single-particle mass spectrometry of tropospheric aerosol particles, J. Geophys. Res., 111, D23S32, doi:10.1029/2006JD007340, 2006. Paatero, P.: Least squares formulation of robust non-negative factor analysis, Chemom. Intell. Lab. Syst., 37, 23–35, 1997. Paredes-Miranda, G., Arnott, W. P., Jimenez, J. L., Aiken, A. C., Gaffney, J. S., and Marley, N. A.: Primary and secondary contributions to aerosol light scattering and absorption in Mexico City during the MILAGRO 2006 campaign, Atmos. Chem. Phys., 9, 3721–3730, doi:10.5194/acp-9-3721-2009, 2009. Park, K., Kittelson, D. B., Zachariah, M. R., and McMurry, P. H.: Measurement of inherent material density of nanoparticle agglomerates, J. Nanopart. Res., 6, 267–272, 2004. 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, doi:10.5194/acp-7-1961-2007, 2007. Petters, M. D., Carrico, C. M., Kreidenweis, S. M., et al.: Cloud condensation nucleation activity of biomass burning aerosol. J. Geophys. Res., 114, D22205, doi: 10.1029/2009JD012353, 2009. Prenni, A. J., Petters, M. D., Kreidenweis, S. M., et al.: Cloud droplet activation of secondary organic aerosol, J. Geophys. Res., 112, D10223, doi:10.1029/2006JD007963, 2007. Quinn, P. K., Bates, T. S., Coffman, D. J., and Covert, D. S.: Influence of particle size and chemistry on the cloud nucleating properties of aerosols, Atmos. Chem. Phys., 8, 1029–1042, doi:10.5194/acp-8-1029-2008, 2008. Raymond, T. M. and Pandis, S. N.: Cloud activation of single-component organic aerosol particles, J Geophys. Res., 107, 4787, doi:10.1029/2002JD002159, 2002. Raymond, T. M. and Pandis, S. N.: Formation of cloud droplets by multicomponent organic particles, J Geophys. Res., 108, 4469, doi:10.1029/2003JD003503, 2003. Riemer, N., Vogel, H., and Vogel, B.: Soot aging time scales in polluted regions during day and night, Atmos. Chem. Phys., 4, 1885–1893, doi:10.5194/acp-4-1885-2004, 2004. Riemer, N., West, M., Zaveri, R. A., and Easter, R. C.: Simulating the evolution of soot mixing state with a particle-resolved aerosol model, J. Geophys. Res., 114, D09202, doi:10.1029/2008JD011073, 2009. 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, doi:10.5194/acp-4-2119-2004, 2004. Roberts, G. C., Artaxo, P., Zhou, J. C., et al.: Sensitivity of CCN spectra on chemical and physical properties of aerosol: A case study from the Amazon Basin, J Geophys. Res., 107, 8070, doi:10.1029/2001JD000583, 2002. Roberts, G. C. and Nenes, A.: A continuous-flow streamwise thermal-gradient CCN chamber for atmospheric measurements, Aerosol Sci. Technol., 39, 206–221, 2005. 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, doi:10.5194/acp-10-3365-2010, 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, doi:10.5194/acp-8-1153-2008, 2008. Salcedo, D., Onasch, T. B., Dzepina, K., et al.: Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with Aerosol Mass Spectrometry: results from the CENICA Supersite, Atmos. Chem. Phys., 6, 925–946, doi:10.5194/acp-6-925-2006, 2006. Salcedo, D., Onasch, T. B., Aiken, A. C., et al: Determination of particulate lead during MILAGRO/MCMA-2006 using Aerosol Mass Spectrometry, Atmos. Chem. Phys., 10, 5371–5389, 2010. doi:10.5194/acp-10-5371-2010, 2010. Sciare, J., Oikonomou, K., Cachier, H., Mihalopoulos, N., Andreae, M. O., Maenhaut, W., and Sarda-Esteve, R.: Aerosol mass closure and reconstruction of the light scattering coefficient over the Eastern Mediterranean Sea during the MINOS campaign, Atmos. Chem. Phys., 5, 2253–2265, doi:10.5194/acp-5-2253-2005, 2005. Seinfeld, J. H. and Pandis, S. N.: Atmospheric Chemistry and Physics, 2nd ed., John Wiley & Sons, Inc., Hoboken, p 371, 2006. Shinozuka, Y., Clarke, A. D., DeCarlo, P. F., Jimenez, J. L., Dunlea, E. J., Roberts, G. C., Tomlinson, J. M., Collins, D. R., Howell, S. G., Kapustin, V. N., McNaughton, C. S., and Zhou, J.: Aerosol optical properties relevant to regional remote sensing of CCN activity and links to their organic mass fraction: airborne observations over Central Mexico and the US West Coast during MILAGRO/INTEX-B, Atmos. Chem. Phys., 9, 6727–6742, doi:10.5194/acp-9-6727-2009, 2009. Shiraiwa, M., Kondo, Y., Moteki, N., et al.: Evolution of mixing state of black carbon in polluted air from Tokyo, Geophys. Res. Lett., 34, L16803, doi:10.1029/2007GL029819, 2007. Shulman, M. L., Jacobson, M. C., Carlson, R. J., et al.: Dissolution behavior and surface tension effects of organic compounds in nucleating cloud droplets, Geophys. Res. Lett., 23, 277–280, 1996. Sotiropoulou, R. E. P., Medina, J., and Nenes, A.: CCN predictions: Is theory sufficient for assessments of the indirect effect? Geophys. Res. Lett., 33, L05816, doi:10.1029/2005GL025148, 2006. Stroud, C. A., Nenes, A., Jimenez, J. L., et al.: Cloud activating properties of aerosol observed during CELTIC, J. Atmos. Sci., 64, 441–459, 2007. Svenningsson, B., Rissler, J., Swietlicki, E., Mircea, M., Bilde, M., Facchini, M. C., Decesari, S., Fuzzi, S., Zhou, J., Monster, J., and Rosenorn, T.: Hygroscopic growth and critical supersaturations for mixed aerosol particles of inorganic and organic compounds of atmospheric relevance, Atmos. Chem. Phys., 6, 1937–1952, doi:10.5194/acp-6-1937-2006, 2006. Textor, C., Schulz, M., Guibert, S., Kinne, S., Balkanski, Y., Bauer, S., Berntsen, T., Berglen, T., Boucher, O., Chin, M., Dentener, F., Diehl, T., Easter, R., Feichter, H., Fillmore, D., Ghan, S., Ginoux, P., Gong, S., Kristjansson, J. E., Krol, M., Lauer, A., Lamarque, J. F., Liu, X., Montanaro, V., Myhre, G., Penner, J., Pitari, G., Reddy, S., Seland, O., Stier, P., Takemura, T., and Tie, X.: Analysis and quantification of the diversities of aerosol life cycles within AeroCom, Atmos. Chem. Phys., 6, 1777-1813, doi:10.5194/acp-6-1777-2006, 2006. Turpin, B. J. and Lim, H. J.: Species contributions to PM2.5 mass concentrations: Revisiting common assumptions for estimating organic mass, Aerosol Sci. Technol., 35, 602–610, 2001. Twomey, S.: Influence of Pollution on Shortwave Albedo of Clouds, J. Atmos. Sci., 34, 1149–1152, 1977. Ulbrich, I. M., Canagaratna, M. R., Zhang, Q., Worsnop, D. R., and Jimenez, J. L.: Interpretation of organic components from Positive Matrix Factorization of aerosol mass spectrometric data, Atmos. Chem. Phys., 9, 2891–2918, doi:10.5194/acp-9-2891-2009, 2009. VanReken, T. M., Rissman, T. A., Roberts, G. C., et al.: Toward aerosol/cloud condensation nuclei (CCN) closure during CRYSTAL-FACE, J Geophys. Res., 108, 4633, doi:10.1029/2003JD003582, 2003. Velasco, E., Pressley, S., Grivicke, R., Allwine, E., Coons, T., Foster, W., Jobson, B. T., Westberg, H., Ramos, R., Hernández, F., Molina, L. T., and Lamb, B.: Eddy covariance flux measurements of pollutant gases in urban Mexico City, Atmos. Chem. Phys., 9, 7325–7342, doi:10.5194/acp-9-7325-2009, 2009. Vestin, A., Rissler, J., Swietlicki, E., et al.: Cloud-nucleating properties of the Amazonian biomass burning aerosol: Cloud condensation nuclei measurements and modeling, J. Geophys. Res., 112, D14201, doi:10.1029/2006JD8104, 2007. Volkamer, R., Jimenez, J. L., San Martini, F., et al.: Secondary Organic Aerosol Formation from Anthropogenic Air Pollution: Rapid and Higher than Expected. Geophys. Res. Lett., 33, L17811, doi:10.1029/2006GL026899, 2006. Wang, J., Flagan, R. C., and Seinfeld, J. H.: A differential mobility analyzer (DMA) system for submicron aerosol measurements at ambient relative humidity, Aerosol Sci. Technol., 37, 46–52, 2003. Wang, J., Lee, Y. N., Daum, P. H., Jayne, J., and Alexander, M. L.: Effects of aerosol organics on cloud condensation nucleus (CCN) concentration and first indirect aerosol effect, Atmos. Chem. Phys., 8, 6325–6339, doi:10.5194/acp-8-6325-2009, 2008. Williams, B. J., Goldstein, A. H., Millet, et al.: Chemical speciation of organic aerosol during the International Consortium for Atmospheric Research on Transport and Transformation 2004: Results from in situ measurements, J. Geophys. Res., 112, D10S26, doi:10.1029/2006JD007601, 2007. Wilson, J., Cuvelier, C., and Raes, F.: A modeling study of global mixed aerosol fields, J. Geophys. Res., 106, 34081–34108, 2001. Zhang, Q., Worsnop, D. R., Canagaratna, M. R., and Jimenez, J. L.: Hydrocarbon-like and oxygenated organic aerosols in Pittsburgh: insights into sources and processes of organic aerosols, Atmos. Chem. Phys., 5, 3289–3311, doi:10.5194/acp-5-3289-2005, 2005a. Zhang, Q., Canagaratna, M. R., Jayne, J. T., et al.: Time and Size-Resolved Chemical Composition of Submicron Particles in Pittsburgh – Implications for Aerosol Sources and Processes. J. Geophys. Res., 110, D07S09, doi:10.1029/2004JD004649, 2005b. Zhang, Q., Jimenez, J. L., Canagaratna, M. R., et al: Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically-influenced Northern Hemisphere midlatitudes, Geophys. Res. Lett., 34, L13801, doi:10.1029/2007GL029979, 2007.