Atmospheric aerosol-cloud-climate interactions (e.g. heterogeneous nucleation, particle oxidation and photosensitization, molecular composition-, phase-, acidity- and structure- changes, ...) are fundamental processes in the atmosphere. Despite the importance of these processes in energy transfer, cloud dynamics, precipitation formation, and hence in climate change, little is known about the molecular mechanism and the respective contribution of different structural and chemical surface properties of the atmospheric aerosols controlling these processes in the atmosphere. For Example, ice particles in the atmosphere, both in cirrus and mixed-phase clouds, contribute to the largest uncertainty in interpretations of the Earth’s changing energy budget. Their large variability in number, size, shape, and surface properties makes it difficult to understand and parameterize their microphysical and hence radiative properties.
Fundamental understanding of the cloud dynamics and aerosol properties, which play the major role in the climate system, will require the understanding of gas-, water-, and ice-aerosol surface interactions. To advance our knowledge about atmospheric processes, this session aims to bring together two research areas, namely (1) Atmospheric Surface Science (ASS) and (2) Ice Nucleating Particles (INP):
(1) ASS is concerned with the experimental and theoretical approaches investigating atmospheric interactions as well as ice nucleation processes “on the molecular level”. The goal is to fill the gap between the large-scale atmospheric processes and gas-, water-, and ice- interactions with atmospherically relevant mineral and biological surfaces.
(2) INP are concerned with the laboratory examination, on a fundamental level, trying to understand the nucleation processes and characterizing INP in the atmosphere.
vPICO presentations: Tue, 27 Apr
Understanding the way in which ice forms is of great importance to many fields of science. Pure water droplets in the atmosphere can remain in the liquid phase to nearly -40º C. Crystallization of ice in the atmosphere therefore typically occurs in the presence of ice nucleating particles (INPs), such as mineral dust or organic particles, which trigger heterogeneous ice nucleation at clearly higher temperatures. The growth of ice is accompanied by a significant release of latent heat of fusion, which causes supercooled liquid droplets to freeze in two stages [Pruppacher and Klett, 1997].
We are studying these topics by utilizing the monatomic water model [Molinero and Moore, 2009] for unbiased molecular dynamics (MD) simulations, where different surfaces immersed in water are cooled below the melting point over tens of nanoseconds of simulation time and crystallization is followed.
With a combination of finite difference calculations and novel moving-thermostat molecular dynamics simulations we show that the release of latent heat from ice growth has a noticeable effect on both the ice growth rate and the initial structure of the forming ice. However, latent heat is found not to be as critically important in controlling immersion nucleation as it is in vapor-to-liquid nucleation [Tanaka et al.2017].
This work was supported by the ERC Grant 692891-DAMOCLES, the Academy of Finland Flagship funding (grant no. 337549), and the University of Helsinki, Faculty of Science ATMATH project. Supercomputing resources were provided by CSC–IT Center for Science, Ltd., Finland.
Pruppacher, H. R. and J. D. Klett (1997). Microphysics of Clouds and Precipitation. Vol. 18. Kluwer Academic.
Molinero, V. and E. B. Moore (2009). J. Phys. Chem. B 113, 4008.
Tanaka, K. K et al. (2017). Phys. Rev. E 96, 022804.
How to cite: Pakarinen, O., Pulido Lamas, C., Roudsari, G., Reischl, B., and Vehkamäki, H.: The role of latent heat in heterogeneous ice nucleation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16164, https://doi.org/10.5194/egusphere-egu21-16164, 2021.
The condensation of carbon dioxide (CO2) is a topic of general interest in view of global decarbonization targets, e.g. in low-temperature CO2 capture technologies promoting the phase transition of CO2 gas is the crucial step. Homogeneous nucleation of a mixture of CO2 and argon gas in a supersonic nozzle has been studied at temperatures from 78 to 92 K, and CO2 partial pressures between 70 and 800 Pa. The consistency between the current data and measurements at higher temperature suggests the critical clusters remain liquid-like even at these low temperatures.
Here we present large-scale atomistic molecular dynamics (MD) simulations of homogenous CO2 nucleation from the vapour phase at temperatures from 75 to 105 K. The MD approach is an unbiased method to study the nucleation process, including the phase and structure of even the smallest clusters. We used argon carrier gas as a heat bath for the CO2 molecules to avoid unphysical removal of latent heat.
Simulations confirm that despite strong undercooling, nucleation proceeds through liquid-like clusters. Also, by applying standard steady-state cluster growth kinetics, we are able to calculate the cluster formation free energies from the MD simulations. The results suggest a curvature correction to the classical liquid drop model used in the classical nucleation theory. The correction depends only on the bulk liquid properties, and hence the simulation-based correction can be applied to predict the nucleation rates of real CO2.
The simulation-based theory is able to capture the magnitude and the temperature-dependency of the nucleation rate rather well, whereas both standard CNT and its self-consistent version (SCNT) underestimate the rate by several orders of magnitude. Here we have corrected the theoretical values with the non-isothermal factor, which is about 0.01-0.1 for the studied system.
How to cite: Tikkanen, V., Dingilian, K., Halonen, R., Reischl, B., Wyslouzil, B., and Vehkamäki, H.: Molecular dynamics simulations of homogeneous CO2 nucleation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15132, https://doi.org/10.5194/egusphere-egu21-15132, 2021.
Dynamic water uptake by aerosol is a major driver of cloud droplet activation and growth. Interfacial mass transfer— that governs water uptake if the mean free path of molecules in the vapour phase is comparable to particle size — is represented in models by the mass accommodation coefficient. Although widely used, this approach neglects i) other internal interfaces (e.g., liquid-liquid that may be important for water uptake), and, ii) fluctuations of the liquid surface from capillary waves that modulate the surface and induce ambiguity in the estimation of mass accommodation coefficients. These issues can be addressed if the full path of the water molecule – from vapour to the bulk aqueous phase - is considered.
We demonstrate, using steered molecular simulations, that a full treatment of the water uptake process reveals important details of the mechanism. The simulations are used to reconstruct the free energy profile of water transport across a vapour/hydroxy cis-pinonic acid/water double interface at 300 K and 200 K. In steered molecular dynamics the transferred molecule is pulled with a finite velocity along an aptly chosen reaction coordinate and the work exerted is used to reconstruct the free energy profile. Due to the finite velocity pulling, this method takes the effect of friction on the transport mechanism into account, which is important for phases of considerably different friction coefficients and is neglected by quasi equilibrium free energy methods. Free energy profiles are used to estimate surface and bulk uptake coefficients and are decomposed into entropic and enthalpic contributions.
Surface accommodation coefficients are unity at both temperatures, while bulk uptake at 300 K from the internal interface is strongly hindered (kb=0.05) by the increased density and molecular order in the first layer of the aqueous phase, which results in decreased orientational entropy. The difference between bulk and surface uptake coefficients also implies that water accumulates in the organic shell, which cannot be predicted using a single uptake coefficient for the whole particle. The minimum of the free energy profile at the organic/water interface, rationalised by increased conformational entropy due to local mixing and the depleted system density, results in a concentration gradient which helps maintain low surface tension and phase separation. Low surface tensions may explain increased CCN activity. These entropic features of the free energy profiles diminish at low temperature, which invokes a completely different mechanism of water uptake. Our results point out the need to describe water uptake in aerosol growth models using a temperature dependent parametrisation.
How to cite: Lbadaoui-Darvas, M., Takahama, S., and Nenes, A.: Temperature Dependent Entropy Driven Water Uptake in Phase Separated Aerosol from Steered Molecular Dynamics and Intrinsic Surface Analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14058, https://doi.org/10.5194/egusphere-egu21-14058, 2021.
The uptake of atmospheric gaseous oxidant such as O3 or the ROx (OH, HO2, RO2) family, have a strong impact on the oxidative capacity of the atmosphere. ,  Last decade, few studies have been carried out on the uptake of such compounds on atmospheric aerosol. However, the large variety of organic compounds provides uptake coefficients with a wide range of order of magnitude. ,  Furthermore, the uptake resulting from the combination of different processes (mass accommodation, bulk diffusion, reactivity), the detailed understanding of such a process is not always accessible through experiments. Theoretical tools such as quantum mechanics (QM) combined with Molecular Mechanics (MM) is one way to investigate separately the different processes.
The ONIOM hybrid QM/MM method  allows to study the reactivity of few molecules in a large system. In our group, a methodology using this computational method have been developed in order to estimate the reactive uptake of gaseous compounds onto organic aerosol particles. In this presentation, reactive uptake of HO2 and O3 onto glutaric acid and oleic acid aerosols respectively will be discussed. Comparisons will be addressed with gas phase theoretical reaction rates and with experimental data.
We acknowledge support by the French government through the Program “Investissement d'avenir” through the Labex CaPPA (contract ANR-11-LABX-0005-01) and I-SITE ULNE project OVERSEE (contract ANR-16-IDEX-0004), CPER CLIMIBIO (European Regional Development Fund, Hauts de France council, French Ministry of Higher Education and Research) and French national supercomputing facilities (grants DARI x2016081859 and A0050801859).
 H. L. Macintyre and M. J. Evans, “Parameterisation and impact of aerosol uptake of HO2 on a global tropospheric model,” Atmos. Chem. Phys., vol. 11, no. 21, pp. 10965–10974, Nov. 2011, doi: 10.5194/acp-11-10965-2011.
 M. Zeng and K. R. Wilson, “Efficient Coupling of Reaction Pathways of Criegee Intermediates and Free Radicals in the Heterogeneous Ozonolysis of Alkenes,” The Journal of Physical Chemistry Letters, Jul. 2020, doi: 10.1021/acs.jpclett.0c01823.
 P. S. J. Lakey, I. J. George, L. K. Whalley, M. T. Baeza-Romero, and D. E. Heard, “Measurements of the HO2 Uptake Coefficients onto Single Component Organic Aerosols,” Environ. Sci. Technol., vol. 49, no. 8, pp. 4878–4885, Apr. 2015, doi: 10.1021/acs.est.5b00948.
 M. Mendez, N. Visez, S. Gosselin, V. Crenn, V. Riffault, and D. Petitprez, “Reactive and Nonreactive Ozone Uptake during Aging of Oleic Acid Particles,” J. Phys. Chem. A, vol. 118, no. 40, pp. 9471–9481, Oct. 2014, doi: 10.1021/jp503572c.
 L. W. Chung et al., “The ONIOM Method and Its Applications,” Chem. Rev., vol. 115, no. 12, pp. 5678–5796, Jun. 2015, doi: 10.1021/cr5004419.
How to cite: Roose, A., Duflot, D., Fotsing Kwetche, C., and Toubin, C.: Investigation of the behavior of tropospheric relevant compounds at the interface gas/organic acid aerosols: An ONIOM QM/MM study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11910, https://doi.org/10.5194/egusphere-egu21-11910, 2021.
Ice clouds play an important role in the Earth’s radiative budget and hence climate. Heterogeneous ice nucleation, a major pathway for ice formation in cirrus and mixed-phase clouds, is induced by active sites present on atmospheric aerosol particles termed as ice-nucleating particles. Feldspars have been shown to be highly ice nucleation active. Despite the importance of mineral dusts for ice nucleation, the role of atmospheric aging (e.g. surface alteration due to interactions with chemical species) on their ice nucleation efficiency is largely unknown. This is primarily due to the lack of microscopic level insight into nucleation from laboratory/field-based experiments, due to the inability to experimentally access the small spatial and temporal scales at which nucleation process occurs – a problem that can be potentially tackled with computer simulations. We utilize direct Molecular Dynamics simulations (GROMACS 5.1.4) to investigate the interactions of solutes with different surfaces of potassium feldspar mineral (microcline) and the corresponding interfacial water structure at a microscopic scale. We investigated the interactions of monovalent cations (H3O+, (NH4)+, Li+, K+, Cs+) with various surfaces of microcline, and subsequent effects on the near-surface water structure at 300 K. The investigated surfaces include the perfect cleavage planes, (001) and (010), as well as the high energy plane (100) of microcline. Feldspar is modeled as semi-rigid (lattice atoms fixed expect K+ and H of surface OH) and as fully flexible (all lattice atoms free to move) with the CLAYFF force field, and the TIP4P/Ice model is employed for water. Results show that on simulation timescales, lattice vibration is necessary for ion exchange between added cation and lattice K+, albeit at different exchange rates for the 3 planes. None of the 3 flexible surfaces show any preference for over K+ in terms of ion exchange within the simulation timescale. Both the semi-rigid and flexible surfaces show higher adsorption of molecular cations ((NH4)+ and H3O+) compared with the simple spherical cations. In addition, we do not observe ice nucleation on modified microcline surfaces (both semi-rigid and flexible) at a supercooled temperature of 230 K within the simulation timescale. To conclude, the presented work provides an improved understanding of the processes modifying the feldspar surfaces in water and aqueous solutions and its possible relevance for ice formation.
How to cite: Kumar, A., Bertram, A. K., and Patey, G. N.: Molecular dynamics approach to assess aqueous alteration of potassium-rich feldspar surfaces, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1410, https://doi.org/10.5194/egusphere-egu21-1410, 2021.
The detailed description of organic aerosols surfaces in the atmosphere remains an open issue, which limits our ability to understand and predict environmental change. Important research questions concern the hydrophobic/hydrophilic character of fresh and aged aerosols and the related influence on water uptake in solid, liquid as well in intermediate state. Also, surface characterization remains big challenge but we find it reachable by conjunction of Molecular Dynamics (MD) simulations and the environmental molecular beam (EMB) experimental method. A picture of the detailed molecular-level behavior of water molecules on organic surfaces is beginning to rise based on detailed experimental and theoretical studies; one example is a recent study that investigates water interactions with solid and liquid n-butanol near the melting point , another example focus on interaction of water with solid nopinone . From the other side, in order to characterize surface properties during and before melting we employ MD simulations of n-butanol, nopinone and valeric acid. Nopinone (C9H14O) is a reaction product formed during oxidation of β-pinene and has been found in both the gas and particle phases of atmospheric aerosol. n-butanol (C4H9OH) is primary alcohol, naturally occurs scarcely and here serves as good representative for alcohols. In the same way valeric acid (CH3(CH2)3COOH) serves as a good representative for a family of carboxylic acids. Valeric acid is, as n-butanol, straight-chain molecule. We show that a classical force field for organic material is able to model crystal and liquid structures. The surface properties near the melting point of the condensed phase are reported, and the hydrophobic and hydrophilic character of the surface layer is discussed. Overall surface melting dynamic is presented and quantified in the terms of structural and geometrical properties. Mixing of a methanol with the solid nopinone surface is examined and hereby presented.
 Johansson, S. M., Lovrić, J., Kong, X., Thomson, E. S., Papagiannakopoulos, P., Briquez, S., Toubin, C, Pettersson, J. B. C. (2019). Understanding water interactions with organic surfaces: environmental molecular beam and molecular dynamics studies of the water–butanol system. Physical Chemistry Chemical Physics. https://doi.org/10.1039/C8CP04151B
 Johansson, S. M., Lovrić, J., Kong, X., Thomson, E. S., Hallquist, M., & Pettersson, J. B. C. (2020). Experimental and Computational Study of Molecular Water Interactions with Condensed Nopinone Surfaces Under Atmospherically Relevant Conditions. The Journal of Physical Chemistry A, acs.jpca.9b10970. https://doi.org/10.1021/acs.jpca.9b10970
Keywords: Molecular Dynamics, organic crystal, organic aerosols, water uptake, surface procesess, molecular level
How to cite: Lovrić, J., Kong, X., Johansson, S. M., Thomson, E. S., and Pettersson, J. B. C.: On the interface of organic aerosols: molecular level understanding of surface melting, mixing and water adsorption/desorption dynamics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8258, https://doi.org/10.5194/egusphere-egu21-8258, 2021.
Céline TOUBIN2 and André Severo Pereira GOMES 3
2,3 Laboratoire de Physique des Lasers, des atomes et des Molécules, Université de Lille, Cité Scientifique, 59655 Villeneuve d’Ascq Cedex, France
E-mail : firstname.lastname@example.org ; email@example.com
Ice plays an essential role as a catalyst for reactions between atmospheric trace gases. The uptake of trace gases to ice has been proposed to have a major impact on geochemical cycles, human health, and ozone depletion in the stratosphere . X-ray photoelectron spectroscopy (XPS) , serves as a powerful technique to characterize the elemental composition of such interacting species due to its surface sensitivity. Given the existence of complex physico-chemical processes such as adsorption, desorption, and migration within ice matrix, it is important to establish a theoretical framework to determine the electronic properties of these species under different conditions such as temperature and concentration. The focus of this work is to construct an embedding methodology employing Density Functional (DFT) and Wave Function Theory (WFT) to model and interpret photoelectron spectra of adsorbed halogenated species on ice surfaces at the core level with the highest accuracy possible.
We make use of an embedding approach utilizing full quantum mechanics to divide the system into subunits that will be treated at different levels of theory .
The goal is to determine core electron binding energies and the associated chemical shifts for the adsorbed halogenated species such as molecular HCl and the dissociated form Cl- at the surface and within the uppermost bulk layer of the ice respectively . The core energy shifts are compared to the data derived from the XPS spectra .
We show that the use of a fully quantum mechanical embedding method, to treat solute-solvent systems is computationally efficient, yet accurate enough to determine the electronic properties of the solute system (halide ion) as well as the long-range effects of the solvent environment (ice).
We acknowledge support by the French government through the Program “Investissement d'avenir” through the Labex CaPPA (contract ANR-11-LABX-0005-01) and I-SITE ULNE project OVERSEE (contract ANR-16-IDEX-0004), CPER CLIMIBIO (European Regional Development Fund, Hauts de France council, French Ministry of Higher Education and Research) and French national supercomputing facilities (grants DARI x2016081859 and A0050801859).
How to cite: Opoku, R. A.: Theoretical core spectroscopy of molecules interacting with ice surfaces , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1094, https://doi.org/10.5194/egusphere-egu21-1094, 2021.
Organic aerosols have been typically considered to be liquid, with equilibration between gas and aerosol phase assumed to be reached within seconds. However, Virtanen et al. (Nature, 2010) suggested that particles in amorphous solid state may also occur in the atmosphere implying that mass transfer between the atmospheric particulate and gas phases may be much slower than initially thought. Experimentally, the direct measurement of the diffusion coefficients of different compounds inside atmospheric organic particles is challenging. Thus, an indirect approach is usually employed, involving viscosity measurements and then estimation of diffusion coefficients via the Stokes-Einstein equation, according to which the diffusion coefficient is inversely proportional to the medium viscosity. However, the corresponding diffusion estimates are highly uncertain, especially for highly viscous aerosols which is the most important case. Molecular simulation methods, such as molecular dynamics (MD), can be an alternative method to determine directly the diffusion rates and the viscosity of the constituents of atmospheric organic particles. MD also provides detailed information of the exact dynamics and motion of the molecules, thus offering a deeper understanding on the underlying mechanisms and interactions.
In the present work, we use equilibrium and non-equilibrium MD simulations to estimate the viscosity and diffusion coefficients of bulk systems of representative organic compounds with different chemical structures and physicochemical characteristics. Hydrophilic and hydrophobic compounds representative of primary and secondary oxidized organic products and of primary organic compounds emitted by various sources are considered. The viscosity and self-diffusion coefficients calculated by our simulations are in good agreement with available experimentally measured values. Our results confirm that the presence of carboxyl and hydroxyl groups in the molecule increases the viscosity. The number of carboxyl and hydroxyl groups, in particular, seems to have a good effect on diffusivity (the diffusivity decreases as the number of these functional groups increase), and to a lesser extent on the viscosity. We also discuss the role of the hydrogen bonds formed between these functional groups.
How to cite: Karadima, K. S., Mavrantzas, V. G., and Pandis, S. N.: Diffusion coefficients and viscosities of organic aerosol components through equilibrium and non-equilibrium molecular dynamics simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4141, https://doi.org/10.5194/egusphere-egu21-4141, 2021.
Primary biological aerosol particles (PBAPs) play an important role in mixed-phase clouds as they nucleate ice even at temperatures of T > -10 °C. Current parameterizations of PBAP ice nucleation are based on ice nucleation active surface site (INAS) densities that are derived from freezing experiments. However, only a small fraction of the PBAP surface is responsible for their ice nucleation activity, such as proteins of bacteria cells, fungal spores, pollen polysaccharides and other (unidentified) macromolecules. Based on literature data, we refine the INAS density parameterizations by further parameters:
1) We demonstrate that the ice nucleation activity of such individual macromolecules is much higher than that of PBAPs. It can be shown that INAS of PBAPs can be scaled by the surface fraction of these ice-nucleating molecules.
2) Previous studies suggested that ice nucleation activity tends to be higher for larger macromolecules and their aggregates. We show that these trends hold true for various groups of macromolecules that comprise PBAPs.
Based on these trends, we suggest a more refined parameterization for ice-nucleating macromolecules in different types of PBAPs and even for different species of bacteria, fungi, and pollen. This new parameterization can be considered a step towards a molecular-based approach to predict the ice nucleation activity of the macromolecules in PBAPs based on their biological and chemical properties.
We implement both the traditional INAS parameterization for complete PBAPs and our parameterization for individual molecules in an adiabatic cloud parcel model. The extent will be discussed to which the two parameterizations result in different cloud properties of mixed-phase clouds.
How to cite: Zhang, M., Khaled, A., Amato, P., Delort, A.-M., and Ervens, B.: Towards a molecular-based parameterization of the ice nucleation activity of biological macromolecules and its implications for aerosol-cloud interactions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2073, https://doi.org/10.5194/egusphere-egu21-2073, 2021.
Bacterial ice-nucleating proteins (INPs) promote heterogeneous ice nucleation better than any known material. On the molecular scale, bacterial INPs are believed to function by organizing water into ice‑like patterns to enable the formation of embryonic crystals. However, the details of their working mechanism remains largely elusive. Here, we report the results of comprehensive evaluations of environmentally relevant effects such as changes in pH, the presence of ions and temperature on the activity, three-dimensional structure and hydration shell of bacterial ice nucleators using ice affinity purification, high-throughput ice nucleation assays and surface-specific sum-frequency generation spectroscopy.
 Lukas, Max, et al. "Electrostatic Interactions Control the Functionality of Bacterial Ice Nucleators." Journal of the American Chemical Society 142.15 (2020): 6842-6846.
 Lukas, Max, et al. "Interfacial Water Ordering Is Insufficient to Explain Ice-Nucleating Protein Activity." The Journal of Physical Chemistry Letters 12 (2020): 218-223.
How to cite: Schwidetzky, R., Lukas, M., Kunert, A. T., Pöschl, U., Fröhlich-Nowoisky, J., Bonn, M., and Meister, K.: Understanding Bacterial Ice Nucleation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5614, https://doi.org/10.5194/egusphere-egu21-5614, 2021.
Ice nucleating particles (INPs) can initiate ice formation in clouds, which has a large impact on the hydrological cycle and radiative budget of the Earth. Constraints on the concentration and composition of INPs are needed to predict ice formation in clouds and hence the climate. Despite previous INP measurements in the Arctic, our understanding of the concentrations, composition, and sources of Arctic INPs is insufficient. Here we report daily concentrations of INPs at Alert, a ground site in the Canadian High Arctic, during October and November of 2018. The contributions of mineral dust and proteinaceous particles to the total INP population were evaluated by testing the responses of the samples to heat and ammonium treatments. Possible source locations of the most effective INPs were investigated using back-trajectory simulations with a Lagrangian particle dispersion model. The results show that the INP concentrations in October were higher than that in November. Combining our results with previous INP measurements at Alert, a seasonal trend was observed for the INP concentrations at -18 °C and -22 °C, with a higher concentration in the late spring, summer and early fall, and a lower concentration in the early spring, late fall, and winter. For the October samples, proteinaceous INPs were detected at T > -21 °C with a fraction of 60% to 100% and mineral dust INPs were detected at T < -21 °C. For the November samples, proteinaceous INPs were only detected at T > -16 °C with a fraction of 88% to 100% and mineral dust INPs were detected at T < -20 °C. The most effective INPs were possibly from South China and California based on 20-day backward simulations using the FLEXible PARTicle dispersion model and the correlations between INP concentrations and Al, , Na+, and Cl- measured at the site.
How to cite: Yun, J., Evoy, E., Worthy, S., Fraser, M., Veber, D., Platt, A., Anderson, K., Sharma, S., Leaitch, R., and Bertram, A.: The Importance of Mineral Dust and Proteinaceous Ice Nucleating Particles in the Canadian High Artic During the Fall of 2018 , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9455, https://doi.org/10.5194/egusphere-egu21-9455, 2021.
Cloud formation represents a large uncertainty in current climate predictions. In particular, ice in mixed-phase clouds requires the presence of ice nucleating particles (INPs) or ice nucleating macromolecules (INMs). An influential population of INPs has been proposed to be organic sea spray aerosols in otherwise pristine ocean air. However, the interactions between INMs present in sea water and their freezing behavior under atmospheric immersion freezing conditions warrants further research to constrain the role of sea spray aerosols on cloud formation. Indeed, salt is known to lower the freezing temperature of water, through a process called freezing point depression (FPD). Yet, current FPD corrections are solely based on the salt content and assume that the INMs’ ice nucleation abilities are identical with and without salt. Thus, we measured the effect of salt content on the ice nucleating ability of INMs, known to be associated with marine phytoplankton, in immersion freezing experiments in the Freezing Ice Nuclei Counter (FINC) (Miller et al., AMTD, 2020). We measured eight INMs, namely taurine, isethionate, xylose, mannitol, dextran, laminarin, and xanthan as INMs in pure water at temperatures relevant for mixed-phase clouds (e.g. 50% activated fraction at temperatures above –23 °C at 10 mM concentration). Subsequently, INMs were analyzed in artificial sea water containing 36 g salt L-1. Most INMs, except laminarin and xanthan, showed a loss of ice activity in artificial sea water compared to pure water, even after FPD correction. Based on our results, we hypothesize sea salt has an inhibitory effect on the ice activity of INMs. This effect influences our understanding of how INMs nucleate ice as well as challenges our use of FPD correction and subsequent extrapolation to ice activity under mixed-phase cloud conditions.
How to cite: Went, J. F., Wheeler, J. D., Peaudecerf, F. J., and Borduas-Dedekind, N.: The ice nucleating ability of macromolecules in immersion freezing decreases in the presence of salts: Implications for freezing point depression calculations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5914, https://doi.org/10.5194/egusphere-egu21-5914, 2021.
Pummer et al., 2012 found evidence that ice-nucleating particles from birch and conifer pollen are in the macromolecular size category, which has gained attention and verification by the scientific community of atmospheric ice nucleation. Moreover, the abundance of ice-nucleating macromolecules (INMs) is not limited to pollen, as Felgitsch et al., 2018 reported INMs to be extractable from branches, leaves and bark of birches. Furthermore, Seifried et al., 2020 demonstrated the atmospheric relevance of INMs, which are accumulated near the surface of trees, showing that INM are washed out by rain-droplets during rainfall events. However, the chemical composition of INMs still remains poorly understood.
To address atmospheric aerosol measurements to specific INMs, the biochemical identification of INMs is inevitable. To construct a concept, we analyzed birch pollen washing water (BPWW) regarding fluorescence and infrared (IR) spectroscopy. We found that the fluorescent bands of proteins are present in BPWW, however quenched by Quercetin-3O-sophoroside, a strong UV-light absorbing substance. Furthermore, BPWW shows intense IR bands in various regions of sugars. However, after a salting out, filtration and purification procedure, the IR spectra of ice nucleation active solutions show characteristic amide bands suggesting (glyco-)proteins to be one type of INMs from pollen.
Pummer, B. G., Bauer, H., Bernardi, J., Bleicher, S., & Grothe, H. (2012). Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen. Atmospheric Chemistry and Physics, 12(5), 2541.
Felgitsch, L., Baloh, P., Burkart, J., Mayr, M., Momken, M. E., Seifried, T. M., ... & Grothe, H. (2018). Birch leaves and branches as a source of ice-nucleating macromolecules.
Seifried, T. M., Bieber, P., Felgitsch, L., Vlasich, J., Reyzek, F., Schmale III, D. G., & Grothe, H. (2020). Surfaces of silver birch (Betula pendula) are sources of biological ice nuclei: in vivo and in situ investigations. Biogeosciences, 17(22), 5655-5667.
How to cite: Bieber, P., Seifried, T. M., and Grothe, H.: Identification of Ice-Nucleating Macromolecules from Pollen Washing Water, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15225, https://doi.org/10.5194/egusphere-egu21-15225, 2021.
The ice nucleation activity of pollen from silver birch (Betula pendula), pines (e.g. Pinus sylvestris) and other trees has been assigned not only to pollen grains but also to subpollen particles (SPP) and extractable macromolecules, i.e. ice-nucleating macromolecules (INMs) (Pummer et al., 2012). The number concentration of pollen in comparison to other ice-nucleating particles suggests a minor impact to atmospheric cloud glaciation (Hoose et al., 2010). When focusing on macromolecules, the importance of INMs from vegetation, however, needs to be re-evaluated in respect to atmospheric ice nucleation. It has been shown that INMs are present in nearly every tissue of birches (Felgitsch et al., 2018) and furthermore, that the macromolecules are extracted from the surface, when they come into contact with water (Seifried et al., 2020). We hypothesize that extractable INMs from tree surfaces are emitted during rainfall by splash induced emissions and field experiments were performed to evaluate the amount of INMs extracted by rain-droplets. Sampled rainwater, which was splashed off from birch surfaces, revealed INMs in high number concentration (108 cm-2) and can be attributed to the vegetation surface (Seifried et al., 2020). To further investigate emission sources an aerosol sampling tool (including an impinger and an impactor) has been developed and mounted on two rotary-wing drones (Bieber et al., 2020). Aerosol samples were collected in an alpine environment on ground level and above the canopy of birches and pines. We found that the bioaerosol concentration increased after rainfall and collected INMs show a similar onset freezing temperature as birch surface extracts (around -20°C). Microscopic images revealed a fluorescent organic film on aerosol particles, which might be linked to extractable material from bio-surfaces. We suggest splash induced aerosolization of INMs during rainfall to be an underestimated source for atmospheric cloud glaciation, since INMs can easily be carried on larger aerosol particles, e.g. on SPP or on mineral dust particles.
Pummer, B. G., Bauer, H., Bernardi, J., Bleicher, S., and Grothe, H.: Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen, Atmos. Chem. Phys., 12, 2541–2550, https://doi.org/10.5194/acp-12-2541-2012, 2012.
Hoose, C., J. E. Kristjánsson, and S. M. Burrows.: How important is biological ice nucleation in clouds on a global scale?, Environ. Res. Lett., 5, https://doi.org/10.1088/1748-9326/5/2/024009, 2010.
Felgitsch, L., Baloh, P., Burkart, J., Mayr, M., Momken, M. E., Seifried, T. M., Winkler, P., Schmale III, D. G., and Grothe, H.: Birch leaves and branches as a source of ice-nucleating macromolecules, Atmos. Chem. Phys., 18, 16063–16079, https://doi.org/10.5194/acp-18-16063-2018, 2018.
Seifried, T. M., Bieber, P., Felgitsch, L., Vlasich, J., Reyzek, F., Schmale III, D. G., and Grothe, H.: Surfaces of silver birch (Betula pendula) are sources of biological ice nuclei: in vivo and in situ investigations, Biogeosciences, 17, 5655–5667, https://doi.org/10.5194/bg-17-5655-2020, 2020.
Bieber, P.; Seifried, T.M.; Burkart, J.; Gratzl, J.; Kasper-Giebl, A.; Schmale, D.G., III; Grothe, H. A Drone-Based Bioaerosol Sampling System to Monitor Ice Nucleation Particles in the Lower Atmosphere. Remote Sens., 12, 552, 2020.
How to cite: Seifried, T. M., Bieber, P., Kunert, A. T., Schmale III, D. G., Whitmore, K., Pöschl, U., Fröhlich-Nowoisky, J., and Grothe, H.: Bio-Surfaces of Frost Resistant Plants as Source of Ice-Nucleating Macromolecules, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15236, https://doi.org/10.5194/egusphere-egu21-15236, 2021.
Wind pollinated trees such as birch trees release large amounts of pollen to the atmosphere during their blooming season in early spring. Due to the large size of pollen (birch pollen diameter: 20-25 µm) and short residence time in the atmosphere, their impact on cloud formation was believed to be negligible. However, in recent years studies have shown that ice nucleating materials, so called ice nucleating macromolecules (INM), much smaller in size can be extracted from pollen. At the same time there is evidence from medical studies that pollen can rupture under conditions of high humidity in the atmosphere and expel cytoplasmic material including starch granules, commonly referred to as subpollen particles (SPP). INM or SPP are much smaller and potentially more numerous than pollen and could significantly affect cloud formation in the atmosphere.
In this study, we focus on birch pollen and investigate the relationship between pollen grains, INM and SPP. According to the usage of the term SPP in the medical field we define SPP as the starch granules contained in pollen grains. We develop an extraction method to generate large quantities of SPP and investigate their ice nucleation activity. To our knowledge, this is the first study to investigate the ice nucleation activity of isolated SPP. We show that INM are only loosely attached to SPP and that purified SPP are not ice nucleation active: after several times of washing SPP with ultrapure water the ice nucleation activity completely disappears. In addition, we study the chemical nature of the INM with fluorescence spectroscopy and quantify the protein concentration with the Bradford assay. Fluorescence excitation-emission maps indicate a strong signal in the protein range (maximum around λex = 280 nm and λem = 330 nm) that correlates with the ice nucleation activity. In contrast, with purified SPP this signal is lost. The protein concentration ranges from 77.4 μg mL-1 for highly concentrated INM to below 2.5 μg mL-1 for purified SPP. The results thereby indicate a linkage between ice nucleation activity and protein concentration. Purified SPP are not ice nucleation active but could, however, act as carriers of INM and distribute those in the atmosphere.
How to cite: Burkart, J., Gratzl, J., Seifried, T., Bieber, P., and Grothe, H.: Subpollen particles (SPP) of birch as carriers of ice nucleating macromolecules, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14807, https://doi.org/10.5194/egusphere-egu21-14807, 2021.
The Quasi-Liquid Layer on ice observed with NEXAFS
Gabathuler, Y. Manoharan, H. Yang, A. Boucly, A. Luca, M. Ammann, T. Bartels-Rausch
Paul Scherrer Institute, Villigen, Switzerland
As temperature approaches the melting point of ice from below, the hydrogen-bonding network at the air – ice interface evolves from a well-defined hexagonal structure towards more randomly spatialized interactions. The general agreement is that a Quasi-Liquid-Layer (QLL) exists at the surface of the ice, and reports on the thickness of this disordered interfacial layer range from 2 nm to 25 nm at 271 K, depending on the probing technique (atomic force microscopy (AFM), ellipsometry, optical reflectivity, sum-frequency generation (SFG)) . These large differences partly arise from the fact that the different techniques are probing different properties of the interface, and the delicate calibration into the thickness of the QLL contributes greatly to the uncertainty.
We investigate the QLL using Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, as Bluhm and his group did in 2002 . The technique probes Auger electrons emitted upon X-ray absorption, thus, NEXAFS becomes inherently sensitive to the upper few nm of the air-ice interfacial region. This work focuses on the probing depth associated with this method and proposes a comprehensive treatment of the data, to help resolve the discrepancy of current thickness data. The importance of the QLL’s thickness comes from its contribution to environmental science as a reservoir for chemical impurities and as a host of chemical reactions with an impact on atmospheric and cryospheric composition.
We will present a first data set of NEXAFS from neat ice between – 40 °C and 0°C acquired at the ISS endstation at the Swiss Light Source of the Paul Scherrer Institute. Results including error bars will be compared to earlier studies. The preliminary analysis suggests that the interfacial disorder seems to be less pronounced than reported in many earlier studies, very much in agreement with recent SFG  and AFM data .
We thank A. Laso for technical help, SNF for funding (grant 178962)
How to cite: Gabathuler, J., Manoharan, Y., Yang, H., Boucly, A., Artiglia, L., Ammann, M., and Bartels-Rausch, T.: The Quasi-Liquid Layer on ice observed with NEXAFS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15629, https://doi.org/10.5194/egusphere-egu21-15629, 2021.
Gas-particle interfaces play essential roles in the atmosphere and directly influence many atmospheric processes, including gas uptake, halogen chemistry, ozone depletion, and heterogeneous ice nucleation. However, because interfacial processes take place on molecular scales, classical bulk thermodynamic theories are often insufficient to describe interfaces. Also, interfacial processes are challenging to characterize and are often overlooked in current atmospheric chemistry.
For this study, ambient pressure X-ray photoelectron spectroscopy (APXPS) experiments were performed. A surface-promoted sulfate-reducing ammonium oxidation reaction is discovered to spontaneously take place on common inorganic aerosol surfaces undergoing solvation. Several key intermediate species including, S0, HS-, HONO, and NH3(aq) are identified as reaction components associated with the solvation process. Depth profiles of relative species abundance show the surface propensity of key species. The species assignments and depth profile features are supported by classical and first-principle molecular dynamics calculations. A detailed mechanism is proposed to describe the processes that lead to unexpected products during salt solvation. This discovery reveals novel chemistry that is uniquely linked to a solvating surface and has great potential to illuminate current puzzles within heterogeneous chemistry. Lastly, natural salts sampled from saline lakes and playas are examined for this behavior, and provide further evidence of the important roles this surface-promoted redox mechanism may play in nature.
How to cite: Kong, X., Gladich, I., Castarede, D., Thomson, E., Boucly, A., Artiglia, L., Ammann, M., and Pettersson, J.: Surface-Promoted Redox Reactions Occurs Spontaneously on Solvating Salt Surfaces, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-727, https://doi.org/10.5194/egusphere-egu21-727, 2021.
Cirrus clouds have an important influence on the climate since the ice crystal size, concentration and distribution of the clouds determine their radiation properties and effects in the atmosphere. Aviation activities in the high troposphere impact cirrus cloud formation indirectly and significantly, due to aviation contrail evolution and aviation soot particles acting as potential ice nucleating particles (INPs). Soot particles have varying ice nucleation (IN) abilities. In cirrus cloud formation conditions, pore condensation and freezing (PCF) is an important ice formation pathway for soot particles, which requires the particle to have appropriate morphology properties and mesoporous structures. In this study, the morphology and pore size of two kinds of soot were changed by a physical agitation method without any chemical modification. The IN activities of both fresh and agitated soot particles with aggregate sizes, 60, 100, 200 and 400 nm, were tested by the Horizontal Ice Nucleation Chamber (HINC) under mixed phase and cirrus cloud conditions.
In general, the IN results show clear size dependence for particles with the same agitation degree both tested soot samples at all tested temperatures (T) from 218 K to 243 K with a step of 5 K. In addition, all soot particles do not form ice at T > 235 K (homogeneous nucleation temperature, HNT) but ice nucleation was observed well below homogeneous freezing relative humidity (RH) for T < HNT, suggesting PCF as the dominating mechanism rather than deposition nucleation. Furthermore, there are significant differences between agitated and fresh soot particles for both soot samples studied. We observed that all agitated soot particles reach a higher particle activation fraction (AF) value at the same T and RH condition, compared to the same size fresh soot particles. Moreover, 200 and 400 nm agitated soot particles require much lower ice saturation values to reach AF = 0.001 than their fresh counterparts. The enhanced IN abilities of agitated soot particles are attributed to soot aggregate structure compaction thus increasing mesopore occurrence probability induced by physical agitation. Preliminary evidence obtained from the mass measurements of the single aggregates show that agitated soot particles are more dense than fresh soot particles of the same size. Furthermore, soot aggregate morphology comparisons from HR-TEM (high resolution transmission electron microscopy) images, soot-water interaction ability results from DVS (dynamic vapor sorption) tests and micro-pore size distribution results from argon desorption tests will be used to explain the soot particle IN ability promotion induced by compaction.
How to cite: Gao, K., Zhou, C.-W., and Kanji, Z.: Enhanced soot particle ice nucleation ability induced by aggregate compaction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-384, https://doi.org/10.5194/egusphere-egu21-384, 2021.
To improve the precision of climate models, it is paramount to accurately quantify the probability of ice formation under conditions (e.g., temperatures and cooling rates) that closely resemble those in the atmosphere. In recent years, microfluidic approaches have emerged as a new tool in atmospheric research. Polydimethylsiloxane (PDMS) microfluidic chips have been used to study the ice nucleation behavior of aqueous drops containing ice nucleating particles. However, PDMS readily takes up water, which compromises the stability of droplets for prolonged times. Additionally, careful temperature calibration has been required due to significant temperature gradients that arise between the bottom area of the chip that is cooled and the location of the droplets. In contrast to past work, our generated droplets are stored in fluoropolymer tubing that is impermeable to water and is immersed in an ethanol bath. Such a design has two main advantages: (i) small aqueous droplets are stable in the structure for extended periods of time beyond those possible in PDMS chips; and (ii) immersion in a liquid bath reduces the temperature gradient between droplets and chip-bottom since cooling instead occurs over all exposed surfaces. These benefits impart an ability to study individual droplets with diameters that approach the sizes of cloud droplets over several freeze-thaw cycles. Herein, we present our instrument design (with an automated droplet-freezing image detection algorithm) and report data on the nucleation of ice in pure water droplets and in aqueous suspensions of ice-nucleating particles. This work will be used as the basis for future investigations in atmospheric ice nucleation that aim to better constrain the influence of ice-nucleating particles on cloud optical properties and precipitation formation.
How to cite: Shardt, N., Isenrich, F., Rösch, M., Stavrakis, S., Marcolli, C., Kanji, Z. A., deMello, A. J., and Lohmann, U.: Cloud from a chip: Quantifying the activity of ice-nucleating particles in microfluidic droplets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7353, https://doi.org/10.5194/egusphere-egu21-7353, 2021.
Atmospheric ice-nucleating particles (INPs) have substantial cloud-phase feedback, and ambient INP concentration may increase in the Arctic region in response to warming (Murray, Carslaw, and Field, 2020). Currently, there are limited INP observations in the Atlantic sector of the Arctic. With the goal of generating new ambient INP data in this particular region, we have measured and studied INP concentrations from Ny-Ålesund (Spitsbergen, Svalbard) during 2017-2019. More specifically, we collected aerosol particles on membrane filters at the Gruvebadet observatory (approx. 50 m above sea level), where a custom-built isokinetic laminar flow inlet is installed. Individual filters collected aerosol particles for 27 hours (at least) to several days with a constant sampling flow of less than 12.8 LPM, which was regulated by a critical orifice. Our sampling periods were intermittent, but covering all meteorological seasons overall. With these filter samples, we have conducted the offline immersion measurements to produce the INP number concentration dataset at temperatures above -25 °C. We will also present the comparison of our immersion data to previous Arctic INP data. Such data would be invaluable to constrain current atmospheric models and estimate their potential impact on aerosol-cloud-climate interactions in the Arctic region.
The authors acknowledge the personnel of the Arctic Station Dirigibile Italia of the National Research Council of Italy for their support to the particle sampling. We also acknowledge contributions of C. A. Rodriguez and H.S. Vepuri for their technical support on WT-CRAFT measurements. This material is based upon work supported by the National Science Foundation under Grant No. 1941317 (CAREER: The Role of Ice-Nucleating Particles and Their Feedback on Clouds in Warming Arctic Climate). The authors acknowledge the NySMAC, Ny-Ålesund Atmosphere Research Flagship Programme, for allowing the organization of a collaborative workshop meeting held in Bologna, Italy, in 2017. The workshop provided a venue for authors to come together that fostered this collaboration.
Murray, B. J., Carslaw, K. S., and Field, P. R.: Opinion: Cloud-phase climate feedback and the importance of ice-nucleating particles, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2020-852, in review, 2020.
How to cite: Hou, Y., Wilbourn, E., Hiranuma, N., Bruschi, F., Cappelletti, D., Gravina, P., and Mazzola, M.: Abundance of ice-nucleating particles from the Gruvebadet observatory in Svalbard during 2017-2019, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5784, https://doi.org/10.5194/egusphere-egu21-5784, 2021.
Ice-nucleating particles (INPs) are aerosol particles that catalyze the heterogeneous formation of ice crystals under ice supersaturation conditions. These INPs can change cloud characteristics on wide spatiotemporal scales, including albedo and radiative effects, as well as precipitation types and amounts, thus affecting both weather and climate. However, INP measurements with reasonable temporal resolution have been challenging in terms of both technology and logistics in our research community. Here we present preliminary results of our recent six-month effort from the Eastern North Atlantic (ENA) field campaign to advance the research and explore remote operation of the plug-and-play Portable Ice Nucleation Experiment (PINE) chamber to semi-autonomously measure marine boundary layer INP concentrations. In this campaign we deployed our PINE chamber at the U.S. Department of Energy Atmospheric Radiation Measurement (DOE ARM) ENA site on Graciosa Island, Azores (39° 5′ 29.76″ N, 28° 1′ 32.52″ W). The PINE chamber has been continuously operated since October 2020 with supervision and periodic remote maintenance by scientists in West Texas. The INP measurements were conducted at mixed-phase cloud conditions at temperatures between -14°C and -33°C. These measurements, along with other aerosol particle and meteorological measurements made by a suite of instruments collocated at the DOE ARM site, give unique insights on the response of INP concentrations to local and mesoscale dynamics and thermodynamic processes. This study provides the first remote and continuous INP measurements over two meteorological seasons made in the ENA region within the marine boundary layer, giving insights into an area with prominent marine influences on aerosol populations. Graciosa Island is a small island (only 61 km2) surrounded by oligotrophic oceans, and these measurements were made during the most biologically productive time of year for phytoplankton in the surrounding ocean waters. The long-term and continuous nature of these measurements allows a unique comparison of marine biological productivity, using satellite-derived chlorophyll a as a proxy for biomass, and INP concentrations. The median INP concentrations at -25 °C and -30 °C were around 4 INP L-1 and 27 INP L-1 respectively. Our preliminary data suggest that INP concentrations measured by the PINE chamber at the ENA site are comparable to other studies at locations with primarily marine INPs. More details will be offered in our presentation.
How to cite: Wilbourn, E., Hiranuma, N., Lacher, L., Nadolny, J., and Möhler, O.: Remotely-controlled ice-nucleating particle measurements from the Eastern North Atlantic during autumn and winter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6314, https://doi.org/10.5194/egusphere-egu21-6314, 2021.
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