ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-11-5539-2011 Ice nucleation from aqueous NaCl droplets with and without marine diatoms Alpert P. A. 1 Aller J. Y. 2 Knopf D. A. 1 Institute for Terrestrial and Planetary Atmospheres/School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000, USA School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000, USA 16 06 2011 11 12 5539 5555 Copyright: © 2011 P. A. Alpert et al. 2011 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/11/5539/2011/acp-11-5539-2011.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/11/5539/2011/acp-11-5539-2011.pdf

Ice formation in the atmosphere by homogeneous and heterogeneous nucleation is one of the least understood processes in cloud microphysics and climate. Here we describe our investigation of the marine environment as a potential source of atmospheric IN by experimentally observing homogeneous ice nucleation from aqueous NaCl droplets and comparing against heterogeneous ice nucleation from aqueous NaCl droplets containing intact and fragmented diatoms. Homogeneous and heterogeneous ice nucleation are studied as a function of temperature and water activity, <i>a</i><sub>w</sub>. Additional analyses are presented on the dependence of diatom surface area and aqueous volume on heterogeneous freezing temperatures, ice nucleation rates, &omega;<sub>het</sub>, ice nucleation rate coefficients, <i>J</i><sub>het</sub>, and differential and cumulative ice nuclei spectra, <i>k(T)</i> and <i>K(T)</i>, respectively. Homogeneous freezing temperatures and corresponding nucleation rate coefficients are in agreement with the water activity based homogeneous ice nucleation theory within experimental and predictive uncertainties. Our results confirm, as predicted by classical nucleation theory, that a stochastic interpretation can be used to describe the homogeneous ice nucleation process. Heterogeneous ice nucleation initiated by intact and fragmented diatoms can be adequately represented by a modified water activity based ice nucleation theory. A horizontal shift in water activity, &Delta;<i>a</i><sub>w, het</sub> = 0.2303, of the ice melting curve can describe median heterogeneous freezing temperatures. Individual freezing temperatures showed no dependence on available diatom surface area and aqueous volume. Determined at median diatom freezing temperatures for <i>a</i><sub>w</sub> from 0.8 to 0.99, &omega;<sub>het</sub><u>~</u>0.11<sup>+0.06</sup><sub>&minus;0.05</sub> s<sup>−1</sup>, <i>J</i><sub>het</sub><u>~</u>1.0<sup>+1.16</sup><sub>&minus;0.61</sub>&times;10<sup>4</sup> cm<sup>−2</sup> s<sup>−1</sup>, and <i>K</i><u>~</u>6.2<sup>+3.5</sup><sub>&minus;4.1</sub> &times;10<sup>4</sup> cm<sup>−2</sup>. The experimentally derived ice nucleation rates and nuclei spectra allow us to estimate ice particle production which we subsequently use for a comparison with observed ice crystal concentrations typically found in cirrus and polar marine mixed-phase clouds. Differences in application of time-dependent and time-independent analyses to predict ice particle production are discussed.

 References Albrecht,&nbsp;B.&nbsp;A.: Aerosols, cloud microphysics, and fractional cloudiness, Science, 245, 1227–1230, 1989. Aller,&nbsp;J.&nbsp;Y., Kuznetsova,&nbsp;M.&nbsp;R., Jahns,&nbsp;C.&nbsp;J., and Kemp,&nbsp;P.: The sea surface microlayer as a source of viral and bacterial enrichment in marine aerosols, J.&nbsp;Aerosol. Sci., 36, 801–812, 2005. Alvain,&nbsp;S., Moulin,&nbsp;C., Dandonneau,&nbsp;Y., and Loisel,&nbsp;H.: Seasonal distribution and succession of dominant phytoplankton groups in the global ocean: a satellite view, Global Biogeochem. Cy., 22, GB3001, https://doi.org/10.1029/2007GB003154, 2008. Anderson,&nbsp;T.&nbsp;L., Charlson,&nbsp;R.&nbsp;J., Schwartz,&nbsp;S.&nbsp;E., Knutti,&nbsp;R., Boucher,&nbsp;O., Rodhe,&nbsp;H., and Heintzenberg,&nbsp;J.: Climate forcing by aerosols – a hazy picture, Science, 300, 1103–1104, 2003. Andreae,&nbsp;M.&nbsp;O. and Crutzen,&nbsp;P.&nbsp;J.: Atmospheric aerosols: biogeochemical sources and role in atmospheric chemistry, Science, 276, 1052–1058, 1997. Baker,&nbsp;M.&nbsp;B.: Cloud microphysics and climate, Science, 276, 1072–1078, 1997. Baker,&nbsp;M.&nbsp;B. and Peter,&nbsp;T.: Small-scale cloud processes and climate, Nature, 451, 299–300, 2008. Bergeron,&nbsp;T.: On the physics of clouds and precipitation, Proc. 5th Assembly U.G.G.I., Lisbon, 14–23 September, 2, p.&nbsp;156, 1935. Bertram,&nbsp;A.&nbsp;K., Koop,&nbsp;T., Molina,&nbsp;L.&nbsp;T., and J.,&nbsp;M.&nbsp;M.: Ice formation in \chem{(NH_4)_2SO_4}-H<sub>2O</sub> particles, J.&nbsp;Phys. Chem.&nbsp;A, 104, 584–588, 2000. Bigg,&nbsp;E.&nbsp;K.: The supercooling of water, P.&nbsp;Phys. Soc.&nbsp;B, 66, 688–694, 1953. Bigg,&nbsp;E.&nbsp;K.: Ice nucleus concentrations in remote areas, J.&nbsp;Atmos. Sci., 30, 1153–1157, 1973. Bigg,&nbsp;E.&nbsp;K.: Ice forming nuclei in the high Arctic, Tellus&nbsp;B, 48, 223–233, 1996. Bigg,&nbsp;E.&nbsp;K. and Leck,&nbsp;C.: Cloud-active particles over the central Arctic Ocean, J.&nbsp;Geophys. Res., 106(D23), 32155–32166, https://doi.org/10.1029/1999JD901152, 2001. Bigg,&nbsp;E.&nbsp;K. and Leck,&nbsp;C.: The composition of fragments of bubbles bursting at the ocean surface, J.&nbsp;Geophys. Res., 113, D11209, https://doi.org/10.1029/2007jd009078, 2008. Blanchard,&nbsp;D.&nbsp;C.: Bubble scavenging and water-to-air-transfer of organic material in the sea, Adv. Chem. Ser., 145, 360–387, 1975. Blanchard,&nbsp;D.&nbsp;C. and Syzdek,&nbsp;L.: Mechanism for water-to-air transfer and concentration of bacteria, Science, 170, 626–628, 1970. Borys,&nbsp;R.&nbsp;D.: The effects of long range transport of air pollutants on Arctic cloud active aerosol, Ph.D. thesis, Dept. Atmos. Sci. Colorado State Univ., Ft.&nbsp;Collins, USA, 1983. Brock, C.&nbsp;A., Cozic, J., Bahreini, R., Froyd, K.&nbsp;D., Middlebrook, A.&nbsp;M., McComiskey, A., Brioude, J., Cooper, O.&nbsp;R., Stohl, A., Aikin, K.&nbsp;C., de&nbsp;Gouw, J.&nbsp;A., Fahey, D.&nbsp;W., Ferrare, R.&nbsp;A., Gao, R.-S., Gore, W., Holloway, J.&nbsp;S., H{ü}ebler, G., Jefferson, A., Lack, D.&nbsp;A., Lance, S., Moore, R.&nbsp;H., Murphy, D.&nbsp;M., Nenes, A., Novelli, P.&nbsp;C., Nowak, J.&nbsp;B., Ogren, J.&nbsp;A., Peischl, J., Pierce, R.&nbsp;B., Pilewskie, P., Quinn, P.&nbsp;K., Ryerson, T.&nbsp;B., Schmidt, K.&nbsp;S., Schwarz, J.&nbsp;P., Sodemann, H., Spackman, J.&nbsp;R., Stark, H., Thomson, D.&nbsp;S., Thornberry, T., Veres, P., Watts, L.&nbsp;A., Warneke, C., and Wollny, A.&nbsp;G.: Characteristics, sources, and transport of aerosols measured in spring 2008 during the aerosol, radiation, and cloud processes affecting Arctic Climate (ARCPAC) Project, Atmos. Chem. Phys., 11, 2423–2453, https://doi.org/10.5194/acp-11-2423-2011, 2011. Brown,&nbsp;R.&nbsp;M., Larson,&nbsp;D.&nbsp;A., and Bold,&nbsp;H.&nbsp;C.: Airborne algae: their abundance and heterogeneity, Science, 143, 583–585, 1964. Burrows,&nbsp;S.&nbsp;M., Butler,&nbsp;T., Jöckel,&nbsp;P., Tost,&nbsp;H., Kerkweg,&nbsp;A., Pöschl,&nbsp;U., and Lawrence,&nbsp;M.&nbsp;G.: Bacteria in the global atmosphere – Part&nbsp;2: Modeling of emissions and transport between different ecosystems, Atmos. Chem. Phys., 9, 9281–9297, https://doi.org/10.5194/acp-9-9281-2009, 2009a. Burrows,&nbsp;S.&nbsp;M., Elbert,&nbsp;W., Lawrence,&nbsp;M.&nbsp;G., and Pöschl,&nbsp;U.: Bacteria in the global atmosphere – Part&nbsp;1: Review and synthesis of literature data for different ecosystems, Atmos. Chem. Phys., 9, 9263–9280, https://doi.org/10.5194/acp-9-9263-2009, 2009b. Cantrell,&nbsp;W. and Heymsfield,&nbsp;A.: Production of ice in tropospheric clouds: a review, B.&nbsp;Am. Meteorol. Soc., 86, 795–807, 2005. Chalmers,&nbsp;M.&nbsp;O., Harper,&nbsp;M.&nbsp;A., and Marshall,&nbsp;W.&nbsp;A.: An Illustrated Catalogue of Airborne Microbiota from the Maritime Antarctic, British Antarctic Survey, National Environmental Research Council, High Cross, Madingley Road, Cambridge, CB3 0ET, UK, 1–175, 1996. Charlson,&nbsp;R.&nbsp;J., Schwartz,&nbsp;S.&nbsp;E., Hales,&nbsp;J.&nbsp;M., Cess,&nbsp;R.&nbsp;D., Coakley,&nbsp;J.&nbsp;A., Hansen,&nbsp;J.&nbsp;E., and Hofmann,&nbsp;D.&nbsp;J.: Climate forcing by anthropogenic aerosols, Science, 255, 423–430, 1992. Clarke,&nbsp;E.&nbsp;C.&nbsp;W. and Glew,&nbsp;D.&nbsp;N.: Evaluation of the thermodynamic functions for aqueous sodium-chloride from equilibrium and calorimetric measurements below 154 {\degree}C, J.&nbsp;Phys. Chem. Ref. Data, 14, 489–610, 1985. Clegg,&nbsp;S.&nbsp;L., Brimblecombe,&nbsp;P., and Wexler,&nbsp;A.&nbsp;S.: A thermodynamic model of the system \chem{H^+}–\chem{NH_4^+}–\chem{Na^+}–\chem{SO_4^{2-}}–\chem{NO_3^-}–\chem{Cl^-}–H<sub>2O</sub> at 298.15 K, J.&nbsp;Phys. Chem.&nbsp;A, 102, 2155–2171, available online at: <a href="http://www.aim.env.uea.ac.uk/aim/aim.php">http://www.aim.env.uea.ac.uk/aim/aim.php</a> (last access: May&nbsp;2010), 1998. Cziczo,&nbsp;D.&nbsp;J., Murphy,&nbsp;D.&nbsp;M., Hudson,&nbsp;P.&nbsp;K., and Thomson,&nbsp;D.&nbsp;S.: Single particle measurements of the chemical composition of cirrus ice residue during CRYSTAL-FACE, J.&nbsp;Geophys. Res., 109, D04201, https://doi.org/10.1029/2003JD004032, 2004. Dall'Osto,&nbsp;M., Ceburnis,&nbsp;D., Martucci,&nbsp;G., Bialek,&nbsp;J., Dupuy,&nbsp;R., Jennings,&nbsp;S.&nbsp;G., Berresheim,&nbsp;H., Wenger,&nbsp;J., Healy,&nbsp;R., Facchini,&nbsp;M.&nbsp;C., Rinaldi,&nbsp;M., Giulianelli,&nbsp;L., Finessi,&nbsp;E., Worsnop,&nbsp;D., Ehn,&nbsp;M., Mikkilä,&nbsp;J., Kulmala,&nbsp;M., and O'Dowd,&nbsp;C.&nbsp;D.: Aerosol properties associated with air masses arriving into the North East Atlantic during the 2008 Mace Head EUCAARI intensive observing period: an overview, Atmos. Chem. Phys., 10, 8413–8435, https://doi.org/10.5194/acp-10-8413-2010, 2010. Darwin,&nbsp;C.: An account of the fine dust which often falls on vessels in the Atlantic Ocean, Q.&nbsp;J. Geo. Soc., 2, 26–30, 1846. De&nbsp;Haan,&nbsp;D.&nbsp;O., Brauers,&nbsp;T., Oum,&nbsp;K., Stutz,&nbsp;J., Nordmeyer,&nbsp;T., and Finlayson-Pitts,&nbsp;B.&nbsp;J.: Heterogeneous chemistry in the troposphere: experimental approaches and applications to the chemistry of sea salt particles, Int. Rev. Phys. Chem., 18, 343–385, 1999. DeMott,&nbsp;P.&nbsp;J., Rogers,&nbsp;D.&nbsp;C., Kreidenweis,&nbsp;S.&nbsp;M., Chen,&nbsp;Y., Twohy,&nbsp;C.&nbsp;H., Baumgardner,&nbsp;D., Heymsfield,&nbsp;A.&nbsp;J., and Chan,&nbsp;K.&nbsp;R.: The role of heterogeneous freezing in upper tropospheric clouds: inferences from SUCCESS, Geophys. Res. Lett., 25, 1387–1390, 1998. DeMott,&nbsp;P.&nbsp;J., Sassen,&nbsp;K., Poellot,&nbsp;M.&nbsp;R., Baumgardner,&nbsp;D., Rogers,&nbsp;D.&nbsp;C., Brooks,&nbsp;S.&nbsp;D., Prenni,&nbsp;A.&nbsp;J., and Kreidenweis,&nbsp;S.&nbsp;M.: African dust aerosols as atmospheric ice nuclei, Geophys. Res. Lett., 30(14), 1732, https://doi.org/10.1029/2003GL017410, 2003. Dorsey,&nbsp;N.&nbsp;E.: The freezing of supercooled water, T.&nbsp;Am. Philos. Soc., 38, 247–328, 1948. Dowling,&nbsp;D.&nbsp;R. and Radke,&nbsp;L.&nbsp;F.: A summary of the physical properties of cirrus clouds, J.&nbsp;Appl. Meteorol., 29, 970–978, 1990. Fall,&nbsp;R. and Schnell,&nbsp;R.&nbsp;C.: Association of an ice-nucleating <i>Pseudomonad</i> with cultures of the marine <i>Dinoflagellate, heterocapsa-niei</i>, J.&nbsp;Mar. Res., 43, 257–265, 1985. Findeisen,&nbsp;W.: Die kolloidmeteorologischen Vorgänge bei der Niederschlagsbildung (Colloidal meteorological processes in the formation of precipitation), Meteorol.&nbsp;Z., 55, 121–133, 1938. Finlayson-Pitts,&nbsp;B.&nbsp;J.: The tropospheric chemistry of sea salt: a molecular-level view of the chemistry of NaCl and NaBr, Chem. Rev., 103, 4801–4822, 2003. Fisher,&nbsp;N.&nbsp;S. and Wente,&nbsp;M.: The release of trace-elements by dying marine-phytoplankton, Deep-Sea Res. Pt.&nbsp;I, 40, 671–694, 1993. Flyger,&nbsp;H. and Heidam,&nbsp;N.&nbsp;Z.: Ground level measurements of summer tropospheric aerosol in Northern Greenland, J.&nbsp;Aerosol Sci., 9, 157–168, 1978. Forster, P., Ramaswamy, V., Artaxo, P., Berntsen, T., Betts, R., Fahey, D. W., Haywood, J., Lean, J., Lowe, D. C., Myhre, G., Nganga, J., Prinn, R., Raga, G., Schulz, M., and Van Dorland, R.: Changes in Atmospheric Constituents and in Radiative Forcing, in: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, chap. 2, edited by: Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K. B., Tignor, M., and Miller, H. L. Cambridge University Press, Cambridge, UK and New York, NY, USA, 131–234, 2007. Fridlind,&nbsp;A.&nbsp;M., Ackerman,&nbsp;A.&nbsp;S., McFarquhar,&nbsp;G., Zhang,&nbsp;G., Poellot,&nbsp;M.&nbsp;R., DeMott,&nbsp;P.&nbsp;J., Prenni,&nbsp;A.&nbsp;J., and Heymsfield,&nbsp;A.&nbsp;J.: Ice properties of single-layer stratocumulus during the Mixed-Phase Arctic Cloud Experiment: 2. Model results, J.&nbsp;Geophys. Res., 112, D24202, https://doi.org/10.1029/2007jd008646, 2007. Gaudichet,&nbsp;A., Lefévre,&nbsp;R., Gaudry,&nbsp;A., Ardouin,&nbsp;B., Lambert,&nbsp;G., and Miller,&nbsp;J.&nbsp;M.: Mineralogical composition of aerosols at Amsterdam Island, Tellus, 41B, 344–352, 1989. Ghan,&nbsp;S.&nbsp;J., Guzman,&nbsp;G., and Abdul-Razzak,&nbsp;H.: Competition between sea salt and sulfate particles as cloud condensation nuclei, J.&nbsp;Atmos. Sci., 55, 3340–3347, 1998. Guillard,&nbsp;R.&nbsp;R. and Ryther,&nbsp;J.&nbsp;H.: Studies of marine planktonic diatoms: I. <i>Cyclotella nana</i> Hustedt, and <i>Detonula confervacea</i> (Cleve) Gran, Can.&nbsp;J. Microbiol., 8, 229–239, 1962. Haag,&nbsp;W., Kärcher,&nbsp;B., Ström,&nbsp;J., Minikin,&nbsp;A., Lohmann,&nbsp;U., Ovarlez,&nbsp;J., and Stohl,&nbsp;A.: Freezing thresholds and cirrus cloud formation mechanisms inferred from in situ measurements of relative humidity, Atmos. Chem. Phys., 3, 1791–1806, https://doi.org/10.5194/acp-3-1791-2003, 2003. Hakansson,&nbsp;H. and Nihlen,&nbsp;T.: Diatoms of eolian deposits in the Mediterranean, Arch. Protistenk., 138, 313–322, 1990. Hallett,&nbsp;J. and Mossop,&nbsp;S.&nbsp;C.: Production of secondary ice particles during riming process, Nature, 249, 26–28, 1974. Hara, K., Iwasaka, Y., Wada, M., Ihara, T., Shiba, H., Osada, K., and Yamanouchi, T.: Aerosol constituents and their spatial distribution in the free troposphere of coastal Antarctic regions, J. Geophys. Res., 111, D15216, https://doi.org/10.1029/2005JD006591, 2006. Harper,&nbsp;M.&nbsp;A.: Diatoms as markers of atmospheric transport, in: The Diatoms: Applications for the Environmental and Earth Sciences, chap. 22, edited by: Stoermer, E. F. and Smol, J. P., Cambridge University Press, Cambridge, 429–435, 1999. Hegg,&nbsp;D.&nbsp;A. and Baker,&nbsp;M.&nbsp;B.: Nucleation in the atmosphere, Rep. Prog. Phys., 72, 056801, https://doi.org/10.1088/0034-4885/72/5/056801, 2009. Heymsfield,&nbsp;A.&nbsp;J. and McFarquhar,&nbsp;G.&nbsp;M.: Mid-Latitude and Tropical Cirrus: Microphysical Properties, Oxford University Press, 198 Madison Avenue, New York, New York 10016, USA, 2002. Heymsfield,&nbsp;A.&nbsp;J., Miloshevich,&nbsp;L.&nbsp;M., Twohy,&nbsp;C., Sachse,&nbsp;G., and Oltmans,&nbsp;S.: Upper tropospheric relative humidity observations and implications for cirrus ice nucleation, Geophys. Res. Lett., 25, 1343–1350, 1998. Hobbie,&nbsp;J.&nbsp;E., Daley,&nbsp;R.&nbsp;J., and Jasper,&nbsp;S.: Use of nuclepore filters for counting bacteria by fluorescence microscopy, Appl. Enivron. Microb., 33, 1225–1228, 1977. Ikegami, M., Okada, K., Zaizen, Y., and Makino, Y.: Sea-salt particles in the upper tropical troposphere, Tellus Ser. B-Chem. Phys. Meteorol., 46, 142–151, 1994. Ikegami, M., Okada, K., Zaizen, Y., Tsutsumi, Y., Makino, Y., Jensen, J.&nbsp;B., and Gras, J.&nbsp;L.: The composition of aerosol particles in the middle troposphere over the western Pacific Ocean: aircraft observations from Australia to Japan, January 1994, Atmos. Environ., 38, 5945–5956, 2004. Junge,&nbsp;K. and Swanson,&nbsp;B.&nbsp;D.: High-resolution ice nucleation spectra of sea-ice bacteria: implications for cloud formation and life in frozen environments, Biogeosciences, 5, 865–873, https://doi.org/10.5194/bg-5-865-2008, 2008. K{ä}rcher,&nbsp;B. and Lohmann,&nbsp;U.: A parameterization of cirrus cloud formation: heterogeneous freezing, J.&nbsp;Geophys. Res., 108, 4402, https://doi.org/10.1029/2002JD003220, 2003. Kaufman,&nbsp;Y.&nbsp;J., Tanrá,&nbsp;D., and Boucher,&nbsp;O.: A satellite view of aerosols in the climate system, Nature, 419, 215–223, 2002. Kawai,&nbsp;S.: Preliminary observations of the diatoms in atmosphere, Int. Aerobio. Newsl., 15, 6–10, 1981. Kellogg,&nbsp;D.&nbsp;E. and Kellogg,&nbsp;T.&nbsp;B.: Diatoms in South Pole ice: implications for eolian contamination of sirius group deposits, Geology, 24, 115–118, 1996. Knopf,&nbsp;D.&nbsp;A.: Do NAD and NAT form in liquid stratospheric aerosols by pseudoheterogeneous nucleation?, J.&nbsp;Phys. Chem.&nbsp;A, 110, 5745–5750, 2006. Knopf,&nbsp;D.&nbsp;A. and Lopez,&nbsp;M.&nbsp;D.: Homogeneous ice freezing temperatures and ice nucleation rates of aqueous ammonium sulfate and aqueous levoglucosan particles for relevant atmospheric conditions, Phys. Chem. Chem. Phys., 11, 8056–8068, 2009. Knopf,&nbsp;D.&nbsp;A. and Rigg,&nbsp;Y.&nbsp;J.: Homogeneous ice nucleation from aqueous inorganic/organic particles representative of biomass burning: water activity, freezing temperatures, nucleation rates, J.&nbsp;Phys. Chem.&nbsp;A, 115, 762–773, https://doi.org/10.1021/jp109171g, 2011. Knopf,&nbsp;D.&nbsp;A., Koop,&nbsp;T., Luo,&nbsp;B.&nbsp;P., Weers,&nbsp;U.&nbsp;G., and Peter,&nbsp;T.: Homogeneous nucleation of NAD and NAT in liquid stratospheric aerosols: insufficient to explain denitrification, Atmos. Chem. Phys., 2, 207–214, https://doi.org/10.5194/acp-2-207-2002, 2002. Knopf,&nbsp;D.&nbsp;A., Luo,&nbsp;B.&nbsp;P., Krieger,&nbsp;U.&nbsp;K., and Koop,&nbsp;T.: Thermodynamic dissociation constant of the bisulfate ion from raman and ion interaction modeling studies of aqueous sulfuric acid at low temperatures, J.&nbsp;Phys. Chem.&nbsp;A, 107, 4322–4332, 2003. Knopf,&nbsp;D.&nbsp;A., Wang,&nbsp;B., Laskin,&nbsp;A., Moffet,&nbsp;R.&nbsp;C., and Gilles,&nbsp;M.&nbsp;K.: Heterogeneous nucleation of ice on anthropogenic organic particles collected in Mexico City, J.&nbsp;Geophys. Res., 37, L11803, https://doi.org/10.1029/2010GL043362, 2010. Knopf,&nbsp;D.&nbsp;A., Alpert,&nbsp;P.&nbsp;A., Wang,&nbsp;B., and Aller,&nbsp;J.&nbsp;Y.: Stimulation of ice nucleation by marine diatoms, Nat. Geosci., 4, 88–90, https://doi.org/10.1038/ngeo1037, 2011. Koop,&nbsp;T.: Homogeneous ice nucleation in water and aqueous solutions, Z.&nbsp;Phys. Chem., 218, 1231–1258, 2004. Koop,&nbsp;T. and Zobrist,&nbsp;B.: Parameterizations for ice nucleation in biological and atmospheric systems, Phys. Chem. Chem. Phys., 11, 10839–10850, 2009. Koop,&nbsp;T., Luo,&nbsp;B.&nbsp;P., Biermann,&nbsp;U.&nbsp;M., Crutzen,&nbsp;P.&nbsp;J., and Peter,&nbsp;T.: Freezing of HNO<sub>3</sub>/H<sub>2</sub>SO<sub>4</sub>/H<sub>2O</sub> solutions at stratospheric temperatures: nucleation statistics and experiments, J.&nbsp;Phys. Chem.&nbsp;A, 101, 1117–1133, 1997. Koop,&nbsp;T., Ng,&nbsp;H.&nbsp;P., Molina,&nbsp;L.&nbsp;T., and Molina,&nbsp;M.&nbsp;J.: A new optical technique to study aerosol phase transitions: the nucleation of ice from H<sub>2</sub>SO<sub>4</sub> aerosols, J.&nbsp;Phys. Chem.&nbsp;A, 102, 8924–8931, 1998. Koop,&nbsp;T., Kapilashrami,&nbsp;A., Molina,&nbsp;L.&nbsp;T., and Molina,&nbsp;M.&nbsp;J.: Phase transitions of sea-salt/water mixtures at low temperatures: implications for ozone chemistry in the polar marine boundary layer, J.&nbsp;Geophys. Res., 105, 26393–26402, 2000{a}. Koop,&nbsp;T., Luo,&nbsp;B.&nbsp;P., Tsias,&nbsp;A., and Peter,&nbsp;T.: Water activity as the determinant for homogeneous ice nucleation in aqueous solutions, Nature, 406, 611–614, 2000{b}. Kuznetsova,&nbsp;M., Lee,&nbsp;C., and Aller,&nbsp;J.: Characterization of the proteinaceous matter in marine aerosols, Mar. Chem., 96, 359–377, 2005. Lewis,&nbsp;E.&nbsp;R. and Schwartz,&nbsp;S.&nbsp;E.: Comment on "size distribution of sea-salt emissions as a function of relative humidity", Atmos. Environ., 40, 588–590, 2006. Linke,&nbsp;W.&nbsp;F.: Solubilities of Inorganic and Metal Organic Compounds, Am. Chem. Soc., Washington DC, USA, 958–959, 1965. Lohmann,&nbsp;U. and Feichter,&nbsp;J.: Global indirect aerosol effects: a review, Atmos. Chem. Phys., 5, 715–737, https://doi.org/10.5194/acp-5-715-2005, 2005. Marcolli,&nbsp;C., Gedamke,&nbsp;S., Peter,&nbsp;T., and Zobrist,&nbsp;B.: Efficiency of immersion mode ice nucleation on surrogates of mineral dust, Atmos. Chem. Phys., 7, 5081–5091, https://doi.org/10.5194/acp-7-5081-2007, 2007. McComiskey,&nbsp;A., Schwartz,&nbsp;S.&nbsp;E., Schmid,&nbsp;B., Guan,&nbsp;H., Lewis,&nbsp;E.&nbsp;R., Ricchiazzi,&nbsp;P., and Ogren,&nbsp;J.&nbsp;A.: Direct aerosol forcing: calculation from observables and sensitivities to inputs, J.&nbsp;Geophys. Res., 113, D09202, https://doi.org/10.1029/2007JD009170, 2008. McFarquhar,&nbsp;G.&nbsp;M., Zhang,&nbsp;G., Poellot,&nbsp;M.&nbsp;R., Kok,&nbsp;G.&nbsp;L., McCoy,&nbsp;R., Tooman,&nbsp;T., Fridlind,&nbsp;A., and Heymsfield,&nbsp;A.&nbsp;J.: Ice properties of single-layer stratocumulus during the Mixed-Phase Arctic Cloud Experiment: 1.&nbsp;Observations, J.&nbsp;Geophys. Res., 112, D24201, https://doi.org/10.1029/2007jd008633, 2007. McKay,&nbsp;R.&nbsp;M., Barrett,&nbsp;P.&nbsp;J., Harper,&nbsp;M.&nbsp;A., and Hannah,&nbsp;M.&nbsp;J.: Atmospheric transport and concentration of diatoms in surficial and glacial sediments of the Allan Hills, Transantarctic Mountains, Palaeogeo. Palaeocli. Palaeoecol., 260, 168–183, 2008. Mossop,&nbsp;S.&nbsp;C. and Hallett,&nbsp;J.: Ice crystal concentration in cumulus clouds: influence of the drop spectrum, Science, 186, 632–633, 1974. Murphy,&nbsp;D.&nbsp;M. and Koop,&nbsp;T.: Review of the vapour pressures of ice and supercooled water for atmospheric applications, Q.&nbsp;J. Roy. Meteorol. Soc., 131, 1539–1565, 2005. O'Dowd,&nbsp;C.&nbsp;D., Smith,&nbsp;M.&nbsp;H., Consterdine,&nbsp;I.&nbsp;E., and Lowe,&nbsp;J.&nbsp;A.: Marine aerosol, sea-salt, and the marine sulphur cycle: a short review, Atmos. Environ., 31, 73–80, 1997. O'Dowd,&nbsp;C.&nbsp;D., Lowe,&nbsp;J.&nbsp;A., and Smith,&nbsp;M.&nbsp;H.: Coupling sea-salt and sulphate interactions and its impact on cloud droplet concentration predictions, Geophys. Res. Lett., 26, 1311–1314, 1999. O'Dowd,&nbsp;C.&nbsp;D., Facchini,&nbsp;M.&nbsp;C., Cavalli,&nbsp;F., Ceburnis,&nbsp;D., Mircea,&nbsp;M., Decesari,&nbsp;S., Fuzzi,&nbsp;S., Yoon,&nbsp;Y.&nbsp;J., and Putaud,&nbsp;J.&nbsp;P.: Biogenically driven organic contribution to marine aerosol, Nature, 431, 676–680, 2004. Ovadnevaite,&nbsp;J., O'dowd,&nbsp;C., Dall'Osto,&nbsp;M., Ceburnis,&nbsp;D., Worsnop,&nbsp;D.&nbsp;R., and Berresheim,&nbsp;H.: Detecting high contributions of primary organic matter to marine aerosol: a case study, J.&nbsp;Geophys. Res., 38, L02807, https://doi.org/10.1029/2010GL046083, 2011. Phillips,&nbsp;V.&nbsp;T.&nbsp;J., Andronache,&nbsp;C., Christner,&nbsp;B., Morris,&nbsp;C.&nbsp;E., Sands,&nbsp;D.&nbsp;C., Bansemer,&nbsp;A., Lauer,&nbsp;A., McNaughton,&nbsp;C., and Seman,&nbsp;C.: Potential impacts from biological aerosols on ensembles of continental clouds simulated numerically, Biogeosciences, 6, 987–1014, https://doi.org/10.5194/bg-6-987-2009, 2009. Prenni,&nbsp;A.&nbsp;J., Demott,&nbsp;P.&nbsp;J., Rogers,&nbsp;D.&nbsp;C., Kreidenweis,&nbsp;S.&nbsp;M., McFarquhar,&nbsp;G.&nbsp;M., Zhang,&nbsp;G., and Poellot,&nbsp;M.&nbsp;R.: Ice nuclei characteristics from M-PACE and their relation to ice formation in clouds, Tellus&nbsp;B, 61, 436–448, 2009. Pruppacher,&nbsp;H.&nbsp;R. and Klett,&nbsp;J.&nbsp;D.: Microphysics of Clouds and Precipitation, Kluwer Academic Publishers, Dordrecht, The Netherlands, 554 pp., 1997. Radke,&nbsp;L.&nbsp;F., Hobbs,&nbsp;P.&nbsp;V., and Pinnons,&nbsp;J.&nbsp;E.: Observation of cloud condensation nuclei, sodium-containing particles, ice nuclei and the light-scattering coefficient near Barrow, Alaska, J.&nbsp;Appl. Meteorol., 15, 982–995, 1976. Ramanathan,&nbsp;V., Crutzen,&nbsp;P.&nbsp;J., Kiehl,&nbsp;J.&nbsp;T., and Rosenfeld,&nbsp;D.: Aerosols, climate, and the hydrological cycle, Science, 294, 2119–2124, 2001. Rogers,&nbsp;D.&nbsp;C., DeMott,&nbsp;P.&nbsp;J., and Kreidenweis,&nbsp;S.&nbsp;M.: Airborne measurements of tropospheric ice-nucleating aerosol particles in the Arctic spring, J.&nbsp;Geophys. Res., 16, 15053–15063, 2001{a}. Rogers,&nbsp;D.&nbsp;C., DeMott,&nbsp;P.&nbsp;J., Kreidenweis,&nbsp;S.&nbsp;M., and Chen,&nbsp;Y.&nbsp;L.: A continuous-flow diffusion chamber for airborne measurements of ice nuclei, J.&nbsp;Atmos. Ocean. Tech., 18, 725–741, 2001{b}. Rosinski,&nbsp;J., Haagenson,&nbsp;P.&nbsp;L., Nagamoto,&nbsp;C.&nbsp;T., and Parungo,&nbsp;F.: Ice-forming nuclei of maritime origin, J.&nbsp;Aerosol. Sci., 17, 23–46, 1986. Ross,&nbsp;S.&nbsp;M.: Stochastic Processes: Second Edition, Wiley Series in Probability and Mathematical Statistics, New York, NY, USA, Ch.&nbsp;2, "The Poisson Process", 59–98, 1996. Sander,&nbsp;R., Keene,&nbsp;W.&nbsp;C., Pszenny,&nbsp;A.&nbsp;A.&nbsp;P., Arimoto,&nbsp;R., Ayers,&nbsp;G.&nbsp;P., Baboukas,&nbsp;E., Cainey,&nbsp;J.&nbsp;M., Crutzen,&nbsp;P.&nbsp;J., Duce,&nbsp;R.&nbsp;A., Hönninger,&nbsp;G., Huebert,&nbsp;B.&nbsp;J., Maenhaut,&nbsp;W., Mihalopoulos,&nbsp;N., Turekian,&nbsp;V.&nbsp;C., and Van Dingenen,&nbsp;R.: Inorganic bromine in the marine boundary layer: a critical review, Atmos. Chem. Phys., 3, 1301–1336, https://doi.org/10.5194/acp-3-1301-2003, 2003. Schnell,&nbsp;R.&nbsp;C.: Ice nuclei produced by laboratory cultured marine phytoplankton, Geophys. Res. Lett., 2, 500–502, 1975. Schnell,&nbsp;R.&nbsp;C. and Vali,&nbsp;G.: Biogenic ice nuclei, 1.&nbsp;Terrestrial and marine sources, J.&nbsp;Atmos. Sci., 33, 1554–1564, 1976. Sciare,&nbsp;J., Favez,&nbsp;O., Sarda-Esteve,&nbsp;R., Oikonomou,&nbsp;K., Cachier,&nbsp;H., and Kazan,&nbsp;V.: Long-term observations of carbonaceous aerosols in the Austral Ocean atmosphere: evidence of a biogenic marine organic source, J.&nbsp;Geophys. Res., 114, D15302, https://doi.org/10.1029/2009jd011998, 2009. Seifert,&nbsp;M., Ström,&nbsp;J., Krejci,&nbsp;R., Minikin,&nbsp;A., Petzold,&nbsp;A., Gayet,&nbsp;J.-F., Schumann,&nbsp;U., and Ovarlez,&nbsp;J.: In-situ observations of aerosol particles remaining from evaporated cirrus crystals: Comparing clean and polluted air masses, Atmos. Chem. Phys., 3, 1037–1049, https://doi.org/10.5194/acp-3-1037-2003, 2003. Shaffer,&nbsp;B.&nbsp;T. and Lighthart,&nbsp;B.: Survey of culturable airborne bacteria at four diverse locations in Oregon: urban, rural, forest, and coastal, Microb. Ecol., 34, 167–177, 1997. Sorooshian,&nbsp;A., Padro,&nbsp;L.&nbsp;T., Nenes,&nbsp;A., Feingold,&nbsp;G., McComiskey,&nbsp;A., Hersey,&nbsp;S.&nbsp;P., Gates,&nbsp;H., Jonsson,&nbsp;H.&nbsp;H., Miller,&nbsp;S.&nbsp;D., Stephens,&nbsp;G.&nbsp;L., Flagan,&nbsp;R.&nbsp;C., and Seinfeld,&nbsp;J.&nbsp;H.: On the link between ocean biota emissions, aerosol, and maritime clouds: airborne, ground, and satellite measurements off the coast of California, Global Biogeochem. Cy., 23, GB4007, https://doi.org/10.1029/2009gb003464, 2009. Stoermer,&nbsp;E.&nbsp;F. and Smol,&nbsp;J.&nbsp;P. (Eds.): The Diatoms: Applications for the Environmental and Earth Sciences, Cambridge University Press, Cambridge, 1999. Ström,&nbsp;J., Seifert,&nbsp;M., Kärcher,&nbsp;B., Ovarlez,&nbsp;J., Minikin,&nbsp;A., Gayet, J.-F., Krejci,&nbsp;R., Petzold,&nbsp;A., Auriol,&nbsp;F., Haag,&nbsp;W., Busen,&nbsp;R., Schumann,&nbsp;U., and Hansson,&nbsp;H.&nbsp;C.: Cirrus cloud occurrence as function of ambient relative humidity: a comparison of observations obtained during the INCA experiment, Atmos. Chem. Phys., 3, 1807–1816, https://doi.org/10.5194/acp-3-1807-2003, 2003. Tormo,&nbsp;R., Recio,&nbsp;D., Silva,&nbsp;I., and Munoz,&nbsp;A.&nbsp;F.: A quantitative investigation of airborne algae and lichen soredia obtained from pollen traps in South-West Spain, Eur.&nbsp;J. Phycol., 42, 248–252, 2001. Twohy,&nbsp;C.&nbsp;H. and Anderson,&nbsp;J.&nbsp;R.: Droplet nuclei in non-precipitating clouds: composition and size matter, Environ. Res. Lett., 3, 045002, https://doi.org/10.1088/1748-9326/3/4/045002, 2008. Twomey,&nbsp;S.: Pollution and planetary albedo, Atmos. Environ., 8, 1251–1256, 1974. Twomey,&nbsp;S.: Aerosols, clouds and radiation, Atmos. Environ.&nbsp;A-Gen., 25, 2435–2442, 1991. Vali,&nbsp;G.: Quantitative evaluation of experimental results on heterogeneous freezing nucleation of supercooled liquids, J.&nbsp;Atmos. Sci., 29, 402–409, 1971. Vali,&nbsp;G.: Nucleation terminology, J.&nbsp;Aerosol Sci., 16, 575–576, 1985. Vali,&nbsp;G.: Freezing rate due to heterogeneous nucleation, J.&nbsp;Atmos. Sci., 51, 1843–1856, 1994. Vali,&nbsp;G.: Repeatability and randomness in heterogeneous freezing nucleation, Atmos. Chem. Phys., 8, 5017–5031, https://doi.org/10.5194/acp-8-5017-2008, 2008. Verlinde,&nbsp;J., Harrington,&nbsp;J.&nbsp;Y., McFarquhar,&nbsp;G.&nbsp;M., Yannuzzi,&nbsp;V.&nbsp;T., Avramov,&nbsp;A., Greenberg,&nbsp;S., Johnson,&nbsp;N., Zhang,&nbsp;G., Poellot,&nbsp;M.&nbsp;R., Mather,&nbsp;J.&nbsp;H., Turner,&nbsp;D.&nbsp;D., Eloranta,&nbsp;E.&nbsp;W., Zak,&nbsp;B.&nbsp;D., Prenni,&nbsp;A.&nbsp;J., Daniel,&nbsp;J.&nbsp;S., Kok,&nbsp;G.&nbsp;L., Tobin,&nbsp;D.&nbsp;C., Holz,&nbsp;R., Sassen,&nbsp;K., Spangenberg,&nbsp;D., Minnis,&nbsp;P., Tooman,&nbsp;T.&nbsp;P., Ivey,&nbsp;M.&nbsp;D., Richardson,&nbsp;S.&nbsp;J., Bahrmann,&nbsp;C.&nbsp;P., Shupe,&nbsp;M., DeMott,&nbsp;P.&nbsp;J., Heymsfield,&nbsp;A.&nbsp;J., and Schofield,&nbsp;R.: The mixed-phase Arctic cloud experiment, B.&nbsp;Am. Meteorol. Soc., 42, 248–252, 2007. Vogt,&nbsp;R., Crutzen,&nbsp;P.&nbsp;J., and Sander,&nbsp;R.: A mechanism for halogen release from sea-salt aerosol in the remote marine boundary layer, Nature, 383, 327–330, 1996. Watson,&nbsp;S.&nbsp;W., Novitsky,&nbsp;T.&nbsp;J., Quinby,&nbsp;H.&nbsp;L., and Valois,&nbsp;F.&nbsp;W.: Determination of bacterial number and biomass in the marine environment, Appl. Enivron. Microb., 33, 940–946, 1977. Wegener,&nbsp;A.: Thermodynamik der Atmosphäre, Johann Ambrosius Barth, Leipzig, 1911. Welch,&nbsp;H.&nbsp;E., Muir,&nbsp;D.&nbsp;C.&nbsp;G., Billeck,&nbsp;B.&nbsp;N., Lockhart,&nbsp;W.&nbsp;L., Brunskill,&nbsp;G.&nbsp;J., Kling,&nbsp;H.&nbsp;J., Olson,&nbsp;M.&nbsp;P., and Lemoine,&nbsp;R.&nbsp;M.: Brown snow – a long-range transport event in the Canadian Arctic, Environ. Sci. Technol., 25, 280–286, 1991. Wurl,&nbsp;O. and Holmes,&nbsp;M.: The gelatinous nature of the sea-surface microlayer, Mar. Chem., 110, 89–97, 2008. Zhang,&nbsp;K.&nbsp;M., Knipping,&nbsp;E.&nbsp;M., Wexler,&nbsp;A.&nbsp;S., Bhave,&nbsp;P.&nbsp;V., and Tonnesen,&nbsp;G.&nbsp;S.: Size distribution of sea-salt emissions as a function of relative humidity, Atmos. Environ., 39, 3373–3379, 2005. Zobrist,&nbsp;B., Koop,&nbsp;T., Luo,&nbsp;B.&nbsp;P., Marcolli,&nbsp;C., and Peter,&nbsp;T.: Heterogeneous ice nucleation rate coefficient of water droplets coated by a nonadecanol monolayer, J.&nbsp;Phys. Chem.&nbsp;A, 111, 2149–2155, 2007. Zobrist,&nbsp;B., Marcolli,&nbsp;C., Peter,&nbsp;T., and Koop,&nbsp;T.: Heterogeneous ice nucleation in aqueous solutions: the role of water activity, J.&nbsp;Phys. Chem.&nbsp;A, 112, 3965–3975, 2008.