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Daniel Knopf




- Swiss Federal Institute of Technology, Switzerland

Research Topics:

Atmospheric Chemistry, Microphysics and Chemistry of Atmospheric Aerosols, Heterogeneous Atmospheric Chemistry and Kinetics

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  • Bio/Research


    My research focuses on the physical and chemical properties of aerosol particles and their interaction with the atmosphere. Aerosol particles play a key role in air pollution, cloud formation, and global warming. Phase transitions of aerosol particles e.g. the formation of ice and its corresponding impact on the global radiation budget is one of the least understood processes in the atmosphere. Aerosol particles also provide a medium for gas-to-particle reactions, so-called heterogeneous reactions, which can significantly alter atmospheric chemistry. The Antarctic ozone hole is the most prominent example for efficient heterogeneous chemistry. Heterogeneous reactions can change the physical and chemical properties of particles, thus influencing air quality, source apportionment, cloud formation, and climate.

    The growth, crystallization, nucleation, and freezing of aerosol particles are studied in the laboratory under atmospherically relevant conditions. The understanding of these particle phase transitions is crucial to accurately predict the effects of aerosol particles in the atmosphere. The particles studied here range from aqueous inorganic solution droplets and field-collected particles to marine bio-aerosol particles. In the laboratory phase transitions of aerosol particles are investigated using an aerosol nucleation cell coupled to an optical microscope. We use single particle micro-spectroscopic analyses such as computer controlled scanning electron microscopy with energy dispersive analysis of X-rays (CCSEM/EDX) and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS) to infer chemical composition and morphological features of the particles. Continuous development of these experimental techniques is performed to improve our understanding of the microphysical and chemical processes that govern atmospheric aerosol particles.

    Heterogeneous oxidation of particles by atmospheric trace gases such as O3, NO2, N2O5, NO3, and OH are investigated in the laboratory using a flow reactor coupled to a chemical ionization mass spectrometer (CIMS). This approach allows to infer heterogeneous kinetics and products. Additionally, a high-resolution proton-transfer time-of-flight mass spectrometer (HR-PTR-ToF-MS) is applied to determine volatile organic reaction products. Our focus is to study the chemical transformation of biomass burning aerosol particles and its effect on particle water uptake and ice nucleation. Chemical transformation during atmospheric transport of bio-molecular markers representative of biomass burning aerosol can significantly affect aerosol source apportionment. Another research focus lies on the implementation of detailed heterogeneous chemistry in atmospheric models. This allows to assess the importance of various heterogeneous reaction pathways for condensed and gas-phase chemical composition.

  • Publications


    Knopf, D. A., Barry, K. R., Brubaker, T. A., Jahl, L. G., Jankowski, K. A. L., Li, J., Lu, Y., Monroe, L. W., Moore, K. A., Rivera-Adorno, F. A., Sauceda, K. A., Shi, Y., Tomlin, J. M.,  Vepuri, H. S. K., Wang, P., Lata, N. N., Levin, E. J. T., Creamean, J. M., Hill, T. C. J., China, S., Alpert, P. A., Moffet, R. C., Hiranuma, N., Sullivan, R. C., Fridlind, A. M., West, M., Riemer, N., Laskin, A., DeMott, P. J., Liu, X., Aerosol–Ice Formation Closure: A Southern Great Plains Field Campaign, B. Am. Meteorol. Soc., 2021, D-20-0151.1 .

    Ansmann, A., Ohneiser, K., Mamouri, R.-E.,  Knopf, D. A., Veselovskii, I., Baars, H., Engelmann, R., Foth, A., Jimenez, C., Seifert, P., Barja, B., Tropospheric and stratospheric wildfire smoke profiling with lidar: mass, surface area, CCN, and INP retrieval, Atmos. Chem. Phys., 21, 9779–9807, 2021.

    Li, J.,  Knopf, D. A., Representation of Multiphase OH Oxidation of Amorphous Organic Aerosol for Tropospheric Conditions, Environ. Sci. Technol., 55, 11, 7266–7275, 2021.

    Sachin, P., Phillips, V. T. J., Amato, P., Bingemer, H. G., Burrows, S. M., DeMott, P. J.,  Goncalves, F. I. T.,  Knopf, D. A., Morris, C. E., Alwmark, C., Artaxo, P., Pöhlker, C., Schrod, J., Weber, B., Empirical formulation for multiple groups of primary biological ice nucleating particles from field observations over Amazonia, J. Atmos. Sci., 78, 7, 2195–2220, 2021.

    Zaytsev, A., Breitenlechner, M., Novelli, A., Fuchs, H.,  Knopf, D. A., Kroll, J. H., Keutsch, F. N., Application of chemical derivatization techniques combined with chemical ionization mass spectrometry to detect stabilized Criegee intermediates and peroxy radicals in the gas phase, Atmos. Meas. Tech., 14, 2501—2513, 2021.

    Silber, I., Fridlind, A. M., Verlinde, J., Ackerman, A. S., Cesana, G. V.,  Knopf, D. A., The prevalence of precipitation from polar supercooled clouds, Atmos. Chem. Phys., 21, 3949–3971, 2021.

    Li, J., Forrester, S. M.,   Knopf, D. A., Heterogeneous oxidation of amorphous organic aerosol surrogates by O3, NO3, and OH at typical tropospheric temperatures,   Atmos. Chem. Phys., 20, 6055–6080, 2020.

    Knopf, D. A., Alpert, P., Zipori, A., Reicher, N., Rudich, Y., Stochastic nucleation processes and substrate abundance explain time-dependent freezing in supercooled droplets,   npj Climate and Atmospheric Science, 3, 2, 2020.

    Zipori, A., Reicher, N., Erel, Y., Rosenfeld, R., Sandler, A.,   Knopf, D. A., Rudich, Y., The role of secondary ice processes in mid‐latitude continental clouds,   J. Geophys. Res.,  123, 22, 12762–12777, 2018.

    Knopf, D. A., Alpert, P. A., and Wang, B., The Role of Organic Aerosol in Atmospheric Ice Nucleation: A Review,   ACS Earth and Space Chemistry, 2 (3), 168–202, 2018.

    Isaacman-VanWertz, G., Massoli, P., O’Brien, R., Lim, C., Franklin, J. P., Moss, J. A., Hunter, J. F., Nowak, J. B., Canagaratna, M. R., Misztal, P. K., Arata, C., Roscioli, J. R., Herndon, S. T., Onasch, T. B., Lambe, A. T., Jayne, J. T., Su, L.,   Knopf, D. A., Goldstein, A. H., Worsnop, D. R., Kroll, J. H., Chemical evolution of atmospheric organic carbon over multiple generations of oxidation,   Nat. Chem., 10, 462–468, 2018.

    Charnawskas, J. C., Alpert, P. A., Lambe,, A. T., Berkemeier, T., O’Brien, R. E., Massoli, P., Onasch, T. B., Shiraiwa, M., Moffet, R. C., Gilles, M. K., Davidovits, P., Worsnop, D. R.,   Knopf, D. A., Condensed-phase biogenic-anthropogenic interactions with implications for cold cloud formation,   Farad. Discuss., 200, 165-194, 2017.

    Fan, S.,   Knopf, D. A., Heymsfield, A. H., Donner, L. J., Modeling of Aircraft Measurements of Ice Crystal Concentration in the Arctic and a Parameterization for Mixed-Phase Cloud,   J. Atmos. Sci., 74, 3799–3814, 2017.

    Isaacman-VanWertz, G., Massoli, P., O’Brien, R. E., Nowak, J. B., Canagaratna, M. R., Jayne, J. T., Worsnop, D. R., Su, L.,   Knopf, D. A., Misztal, P. K., Arata, C., Goldstein, A. H., Kroll, J. H., Using advanced mass spectrometry techniques to fully characterize atmospheric organic carbon: current capabilities and remaining gaps,   Farad. Discuss., 200, 579-598, 2017.

    China, S., Alpert, P. A., Zhang, B., Schum, S., Dzepina, K., Wright, K., Owen, R. C., Fialho, P., Mazzoleni, L. R., Mazzoleni, C.,   Knopf, D. A., Ice cloud formation potential by free tropospheric particles from long-range transport over the Northern Atlantic Ocean,   J. Geophys. Res., 122, doi:10.1002/2016JD025817, 2017.

    Aller, J. Y., Radway, J. C., Kilthau, W. P., Bothe, D. W., Wilson, T. W., Vaillancourt, R. D., Quinn, P. K., Coffman, D. J., Murray, B. J.,   Knopf, D. A., Size resolved characterization of the polysaccharidic and proteinaceous components of Sea Spray Aerosol,   Atmos. Environ., 154, 331-347, 10.1016/j.atmosenv.2017.01.053, 2017.

    Slade, J. H., M. Shiraiwa, A. Arangio, H. Su, U. Pöschl, J. Wang,   Knopf, D. A., Cloud droplet activation through oxidation of organic aerosol influenced by temperature and particle phase state,   Geophys. Res. Lett., 44, 1583–1591, doi:10.1002/2016GL072424, 2017.

    Laskin, A., Gilles, M. K.,   Knopf, D. A., Wang, B., China, S., Progress in the Analysis of Complex Atmospheric Particles,   Annu. Rev. Anal. Chem., 9, 117-143, 2016.

    Moffet, R. C., O’Brien, R. E., Alpert, P. A., Kelly, S. T., Pham, D. Q., Gilles, M. K.,   Knopf, D. A., Laskin, A., Morphology and mixing of black carbon particles collected in central California during the CARES field study,   Atmos. Chem. Phys., 16, 14515-14525, 2016.

    Wang, B.,   Knopf, D. A., China, S., Arey, B. W., Harder, T. H., Gilles, M. K., Laskin, A., Direct Observation of Ice Nucleation Events on Individual Atmospheric Particles,   Phys. Chem. Chem. Phys., 18, 29721–29731, 2016.

    Pandey, R., Usui, K., Livingstone, R. A., Fischer, S. A., Pfaendtner, J., Backus, E. H. G., Nagata, Y., Fröhlich-Nowoisky, J., Schmüser, L., Mauri, S., Scheel, J. F.,   Knopf, D. A., Pöschl, U., Bonn, M., Weidner, T., Ice-nucleating bacteria control the order and dynamics of interfacial water,   Sci. Adv., 2:e1501630, 2016.

    Alpert, P. A.,   Knopf, D. A., Analysis of isothermal and cooling-rate- dependent immersion freezing by a unifying stochastic ice nucleation model,   Atmos. Chem. Phys., 16, 2083-2107, 2016.

    Ladino, L. A., Yakobi-Hancock, J. D., Kilthau, W. P., Mason, R. H., Si, M., Li, J., Miller, L. A., Schiller, C. L., Huffman, J. A., Aller, J. Y.,   Knopf, D. A., Bertram, A. K., Abbatt, J. P. D., Addressing the ice nucleating abilities of marine aerosol: A combination of deposition mode laboratory and field measurements,   Atmos. Env., 132, 1-10, 2016.

    O'Brien, R. E., Wang, B., Laskin, A., Riemer, N., West, M., Zhang, Q., Sun, Y., Yu, X.-Y., Alpert, P.,   Knopf, D. A., Gilles, M. K., Moffet, R. C., Chemical imaging of ambient aerosol particles: Observational constraints on mixing state parameterization,   J. Geophys. Res., 120, 18, 9591–9605, 2015.

    Alpert, P. A., Kilthau, W. P., Bothe, D. W., Radway, J. C., Aller, J. Y.,   Knopf, D. A., The influence of marine microbial activities on aerosol production: A laboratory mesocosm study,   J. Geophys. Res., 120, 17, 8841–8860, 2015.

    Slade, J. H., Thalman, R., Wang, J.,   Knopf, D. A., Chemical aging of single and multicomponent biomass burning aerosol surrogate particles by OH: implications for cloud condensation nucleus activity,   Atmos. Chem. Phys., 15, 10183–10201, 2015.

    Wilson, T.W., Ladino, L. A., Alpert, P. A., Breckels, M. N., Brooks, I. M., Browse, J., Burrows, S. M., Carslaw, K. S., Huffman, J. A., Judd, C., Kilthau, W. P., Mason, R. H., McFiggans, G., Miller, L. A., Najera, J. Polishchuk, E., Rae, S., Schiller, C. L., Si, M., Vergara Temprado, J., Whale, T. F., Wong, J. P. S., Wurl, O., Yakobi-Hancock, J. D., Abbatt, J. P. D., Aller, J. Y., Bertram, A. K.,   Knopf, D. A., Murray, B. J., A marine biogenic source of atmospheric ice nucleating particles,   Nature, 525, 234–238, 2015.

    Knopf, D. A., Pöschl, U. Shiraiwa, M., Radial Diffusion and Penetration of Gas Molecules and Aerosol Particles through Laminar Flow Reactors, Denuders, and Sampling Tubes,   Anal. Chem., 87 (7), 3746–3754, 2015.

    Arangio, A. M., Slade, J. H., Berkemeier, T., Pöschl, U.,   Knopf, D. A., Shiraiwa, M., Multiphase Chemical Kinetics of OH Radical Uptake by Molecular Organic Markers of Biomass Burning Aerosols: Humidity and Temperature Dependence, Surface Reaction, and Bulk Diffusion,   J. Phys. Chem. A, 119 (19), 4533–4544, 2015.

    Knopf, D. A., Alpert, P. A., Wang, B., O’Brien, R. E., Kelly, S. T., Laskin, A., Gilles, M. K., Moffet, R. C., Micro-Spectroscopic Imaging and Characterization of Individually Identified Ice Nucleating Particles from a Case Field Study, J. Geophys. Res., 119, 17, 10365–10381, 2014.

    Slade, J. H. and   Knopf, D. A., Multiphase OH oxidation kinetics of organic aerosol: The role of particle phase state and relative humidity,   Geophys. Res. Lett.,   41, 14, 5297–5306, 2014.

    Forrester, S. M.,   Knopf, D. A., Photosensitised heterogeneous oxidation kinetics of biomass burning aerosol surrogates by ozone using an irradiated rectangular channel flow reactor,   Atmos. Chem. Phys.,  13, 6507–6522, 2013.

    Rigg, Y. J., Alpert, P. A.,   Knopf, D. A., Immersion freezing of water and aqueous ammonium sulphate droplets initiated by Humic Like Substances as a function of water activity,   Atmos. Chem. Phys., 13, 6603–6622, 2013.

    Knopf, D. A., Alpert, P. A., A Water Activity Based Model of Heterogeneous Ice Nucleation Kinetics for Freezing of Water and Aqueous Solution Droplets, Farad. Disc., 165, 513-534, 2013.

    Slade, J. H.,   Knopf, D. A., Heterogeneous OH oxidation of biomass burning organic aerosol surrogate compounds: Assessment of volatilisation products and the role of OH concentration on the reactive uptake kinetics,   Phys. Chem. Chem. Phys., 15 (16), 5898–5915, 2013.

    Wang, B., Laskin, A., Roedel, T., Gilles, M. K., Moffet, R. C., Tivanski, A. V.,   Knopf, D. A., Heterogeneous ice nucleation and water uptake by field-collected atmospheric particles below 273 K,   J. Geophys. Res., 117, D00V19, 2012.

    Wang, B., Lambe, A. T., Massoli, P., Onasch, T. B., Davidovits, P., Worsnop, D. R.,   Knopf, D. A., The deposition ice nucleation and immersion freezing potential of amorphous secondary organic aerosol: Pathways for ice and mixed-phase cloud formation,   J. Geophys. Res., 117, D16, D16209, 2012.

    Shiraiwa, M., Pöschl, U.,   Knopf, D. A., Multiphase Chemical Kinetics of NO3 Radicals Reacting with Organic Aerosol Components from Biomass Burning.   Environ. Sci. Technol., 46, 6630–6636, 2012.

    Alpert, P. A., Aller, J. Y.,   Knopf, D. A., Initiation of the Ice Phase by Marine Biogenic Surfaces in Supersaturated Gas and Supercooled Aqueous Phases. Special issue “Physics and Chemistry of Water and Ice” of   Phys. Chem. Chem. Phys., 13, 19882-19894, 2011.

    Knopf, D. A., Forrester, S. M., Slade, J. H., Heterogeneous oxidation kinetics of organic biomass burning aerosol surrogates by O3, NO2, N2O5, and NO3. Phys. Chem. Chem. Phys., 13, 21050-21062, 2011.

    Alpert, P. A., Aller, J. Y.,   Knopf, D. A., Ice nucleation from aqueous NaCl droplets with and without marine diatoms,   Atmos. Chem. Phys., 11, 5539–5555, 2011.

    Knopf, D. A., Forrester, S. M., Freezing of Water and Aqueous NaCl Droplets Coated by Organic Monolayers as a Function of Surfactant Properties and Water Activity,   J. Phys. Chem.   A, 115, 5579–5591, 2011.

    Kaiser, J. C., Riemer, N.,   Knopf, D. A., Detailed heterogeneous oxidation of soot surfaces in a particle-resolved aerosol model,   Atmos. Chem. Phys., 11, 4505–4520, 2011.

    Knopf, D. A., Alpert, P. A., Wang, B., Aller, J. Y., Stimulation of Ice Nucleation by Marine Diatoms,   Nat. Geosci., 4, 88–90, 2011.

    Wang, B.,   Knopf, D. A., Heterogeneous ice nucleation on particles composed of humic-like substances impacted by O3,   J. Geophys. Res., 116, D03205, 2011.

    Knopf, D. A., Rigg, Y. J., Homogeneous Ice Nucleation From Aqueous Inorganic Organic Particles Representative of Biomass Burning: Water Activity, Freezing Temperatures, Nucleation Rates,   J. Phys. Chem. A, 115, 762–773, 2011.

    Knopf, D. A., Wang, B., Laskin, A., Moffet, R. C., Gilles, M. K., Heterogeneous nucleation of ice on anthropogenic organic particles collected in Mexico City,   Geophys. Res. Lett., 37, L11803, 2010.

    Springmann, M.,   Knopf, D. A., Riemer, N., Detailed heterogeneous chemistry in an urban plume box model: Reversible co-adsorption of O3, NO2, and H2O on Soot Coated with Benzo[a]pyrene.   Atmos. Chem. Phys., 9, 7461–7479, 2009.

    Knopf, D. A., Lopez, M. D. Homogeneous Ice Freezing Temperatures and Ice Nucleation Rates of Aqueous Ammonium Sulfate and Aqueous Levoglucosan Particles for Relevant Atmospheric Conditions. Special issue “Physical Chemistry of Aerosols” of   Phys. Chem. Chem. Phys., 11, 8056–8068, 2009.

    Cosman, L. M.,   Knopf, D. A., Bertram, A. K., N2O5 reactive uptake on aqueous sulfuric acid solutions coated with branched and straight-chain insoluble organic surfactants,   J. Phys. Chem. A, 112, 2386–2396, 2008.

    Knopf, D. A., Cosman, L. M., Mousavi, P., Mokamati, S., Bertram A. K., A Novel Flow Reactor for Studying Reactions on Liquid Surfaces Coated by Organic Monolayers: Methods, Validation, and Initial Results,   J. Phys. Chem. A, 111, 11021–11032, 2007.

    Knopf, D. A., Reply to “Comment “Do NAD and NAT form in liquid stratospheric aerosols by pseudo-heterogeneous nucleation?””,   J. Phys. Chem. A, 111, 1376–1377, 2007.

    Knopf, D. A., Mak, J., Gross, S., Bertram, A. K.: Does Atmospheric Processing of Saturated Hydrocarbon Surfaces by NO3 Lead to Volatilization?,   Geophys. Res. Lett., 33 (17), L17816, 2006.

    Knopf, D. A., Koop, T., Heterogeneous Nucleation of Ice on Surrogates of Mineral Dust,   J. Geophys. Res., 111 (D12), D12201, 2006.

    Knopf, D. A., Do NAD and NAT form in liquid stratospheric aerosols by pseudoheterogeneous nucleation?,   J. Phys. Chem. A, 110, 5745–5750, 2006.

    Dymarska, M., Murray, B. J., Sun, L., Eastwood, M.,   Knopf, D. A., Bertram, A. K., Ice nucleation on soot at temperatures relevant for the lower troposphere,   J. Geophys. Res., 111 (D4), D04204, 2006.

    Knopf, D. A., Anthony, L. M., Bertram, A. K., Reactive Uptake of O3 by Multicomponent and Multiphase Mixtures Containing Oleic Acid,   J. Phys. Chem. A, 109, 5579–5589, 2005.

    Murray, B. J.,   Knopf, D. A., Bertram, A. K., The formation of cubic ice under conditions relevant to Earth’s atmosphere,   Nature, 434, 202–205, 2005.

    Knopf, D. A., Luo B. P., Krieger, U. K., Koop, T., Reply to “Comment on ‘Thermodynamic Dissociation Constant of the Bisulfate Ion from Raman and Ion Interaction Modeling Studies of Aqueous Sulfuric Acid at Low Temperature”’,   J. Phys. Chem. A, 109, 2707–2709, 2005.

    Parsons, M. T.,   Knopf, D. A., Bertram, A. K., Deliquescence and Crystallization of Ammonium Sulfate Particles Internally Mixed with Water-Soluble Organic Compounds,   J. Phys. Chem. A, 108, 11600–11608, 2004.

    Knopf, D. A., Luo B. P., Krieger, U. K., Koop, T., Thermodynamic Dissociation Constant of the Bisulfate Ion from Raman and Ion Interaction Modeling Studies of Aqueous Sulfuric Acid at Low Temperatures,   J. Phys. Chem. A, 107, 4322–4332, 2003.

    Knopf, D. A., Koop, T., Luo B. P., Weers, U. G., Peter, T., Homogeneous nucleation of NAD and NAT in liquid stratospheric aerosols: insufficient to explain denitrification,   Atmos. Chem. Phys., 2, 207–214, 2002.

    Zink, P.,   Knopf, D. A., Schreiner, J., Mauersberger, K., Möhler, O., Saathof, H., Seifert, M., Tiede, R., Schurath, U., Cryo-chamber simulation of stratospheric H2SO4/H2O particles: Composition analysis and model comparison,   Geophys. Res. Lett., 11 (29), 1551, 2002.

    Schreiner, J., Voigt, C., Zink, P., Kohlmann, A., Knopf, D., Weisser, C., Budz, P., Mauersberger, K., A Mass Spectrometer System for Analysis of Polar Stratospheric Aerosols,   Rev. Sci. Inst., 73, 446–452, 2002.

    Knopf, D. A., Zink, P., Schreiner J., Mauersberger, K., Calibration of an Aerosol Composition Mass Spectrometer with Sulfuric Acid Water Aerosol,   Aerosol Sci. Technol., 35, 924–928, 2001.

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