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1. Ice-nucleating particle concentration measurements from Ny-Ålesund during the Arctic spring–summer in 2018

   https://doi.org/10.5194/acp-21-14725-2021  

   Rinaldi, Matteo ; Hiranuma, Naruki ; Santachiara, Gianni ; Mazzola, Mauro ; Mansour, Karam ; Paglione, Marco ; Rodriguez, Cheyanne A. ; Traversi, Rita ; Becagli, Silvia ; Cappelletti, David ; et al ( January 2021 , Atmospheric Chemistry and Physics)

   Abstract. In this study, we present atmospheric ice-nucleating particle (INP)concentrations from the Gruvebadet (GVB) observatory in Ny-Ålesund(Svalbard). All aerosol particle sampling activities were conducted in April–August 2018. Ambient INP concentrations (nINP) were measured for aerosolparticles collected on filter samples by means of two offline instruments:the Dynamic Filter Processing Chamber (DFPC) and the West Texas CryogenicRefrigerator Applied to Freezing Test system (WT-CRAFT) to assesscondensation and immersion freezing, respectively. DFPC measured nINPs for aset of filters collected through two size-segregated inlets: one fortransmitting particulate matter of less than 1 µm (PM1), theother for particles with an aerodynamic diameter of less than 10 µmaerodynamic diameter (PM10).more »Overall, nINPPM10 measured by DFPC ata water saturation ratio of 1.02 ranged from 3 to 185 m−3 attemperatures (Ts) of −15 to −22 ∘C. On average, the super-micrometer INP (nINPPM10-nINPPM1) accounted forapproximately 20 %–30 % of nINPPM10 in spring, increasing in summer to45 % at −22 ∘C and 65 % at −15 ∘C. This increase in super-micrometer INP fraction towards summer suggests that super-micrometeraerosol particles play an important role as the source of INPs in theArctic. For the same T range, WT-CRAFT measured 1 to 199 m−3. Althoughthe two nINP datasets were in general agreement, a notable nINP offset wasobserved, particularly at −15 ∘C. Interestingly, the results ofboth DFPC and WT-CRAFT measurements did not show a sharp increase in nINPfrom spring to summer. While an increase was observed in a subset of ourdata (WT-CRAFT, between −18 and −21 ∘C), the spring-to-summernINP enhancement ratios never exceeded a factor of 3. More evident seasonal variability was found, however, in our activated fraction (AF) data, calculated by scaling the measured nINP to the total aerosol particleconcentration. In 2018, AF increased from spring to summer. This seasonal AFtrend corresponds to the overall decrease in aerosol concentration towardssummer and a concomitant increase in the contribution of super-micrometer particles. Indeed, the AF of coarse particles resulted markedly higher thanthat of sub-micrometer ones (2 orders of magnitude). Analysis of low-traveling back-trajectories and meteorological conditions at GVB matched to our INP data suggests that the summertime INP population isinfluenced by both terrestrial (snow-free land) and marine sources. Ourspatiotemporal analyses of satellite-retrieved chlorophyll a, as well as spatial source attribution, indicate that the maritime INPs at GVB may comefrom the seawaters surrounding the Svalbard archipelago and/or in proximityto Greenland and Iceland during the observation period. Nevertheless,further analyses, performed on larger datasets, would be necessary to reachfirmer and more general conclusions.« less
2. A new method for operating a continuous-flow diffusion chamber to investigate immersion freezing: assessment and performance study

   https://doi.org/10.5194/amt-13-6631-2020  

   Kulkarni, Gourihar ; Hiranuma, Naruki ; Möhler, Ottmar ; Höhler, Kristina ; China, Swarup ; Cziczo, Daniel J. ; DeMott, Paul J. ( January 2020 , Atmospheric Measurement Techniques)

   Abstract. Glaciation in mixed-phase clouds predominantly occurs through theimmersion-freezing mode where ice-nucleating particles (INPs) immersedwithin supercooled droplets induce the nucleation of ice. Modelrepresentations of this process currently are a large source of uncertaintyin simulating cloud radiative properties, so to constrain these estimates,continuous-flow diffusion chamber (CFDC)-style INP devices are commonly usedto assess the immersion-freezing efficiencies of INPs. This study explored anew approach to operating such an ice chamber that provides maximumactivation of particles without droplet breakthrough and correction factorambiguity to obtain high-quality INP measurements in a manner thatpreviously had not been demonstrated to be possible. The conditioningsection of the chamber wasmore »maintained at −20 ∘C and water relative humidity (RHw) conditions of 113 % to maximize the droplet activation,and the droplets were supercooled with an independentlytemperature-controlled nucleation section at a steady cooling rate(0.5 ∘C min−1) to induce the freezing of droplets andevaporation of unfrozen droplets. The performance of the modified compactice chamber (MCIC) was evaluated using four INP species: K-feldspar,illite-NX, Argentinian soil dust, and airborne soil dusts from an arableregion that had shown ice nucleation over a wide span of supercooledtemperatures. Dry-dispersed and size-selected K-feldspar particles weregenerated in the laboratory. Illite-NX and soil dust particles were sampledduring the second phase of the Fifth International Ice Nucleation Workshop(FIN-02) campaign, and airborne soil dust particles were sampled from anambient aerosol inlet. The measured ice nucleation efficiencies of modelaerosols that had a surface active site density (ns) metric were higher but mostly agreed within 1 order of magnitude compared to results reported in the literature.« less
3. Time-dependent freezing rate parcel model

   https://doi.org/10.5194/acp-15-2071-2015  

   Vali, G. ; Snider, J. R. ( January 2015 , Atmospheric Chemistry and Physics)

   The time-dependent freezing rate (TDFR) model here described represents the formation of ice particles by immersion freezing within an air parcel. The air parcel trajectory follows an adiabatic ascent and includes a period in time when the parcel remains stationary at the top of its ascent. The description of the ice nucleating particles (INPs) in the air parcel is taken from laboratory experiments with cloud and precipitation samples and is assumed to represent the INP content of the cloud droplets in the parcel. Time dependence is included to account for variations in updraft velocity and for the continued formation ofmore »ice particles under isothermal conditions. The magnitudes of these factors are assessed on the basis of laboratory measurements. Results show that both factors give rise to three-fold variations in ice concentration for a realistic range of the input parameters. Refinements of the parameters specifying time dependence and INP concentrations are needed to make the results more specific to different atmospheric aerosol types. The simple model framework described in this paper can be adapted to more elaborate cloud models. The results here presented can help guide decisions on whether to include a time-dependent ice nucleation scheme or a simpler singular description in models.« less
4. Integrating laboratory and field data to quantify the immersion freezing ice nucleation activity of mineral dust particles

   https://doi.org/10.5194/acp-15-393-2015  

   DeMott, P. J. ; Prenni, A. J. ; McMeeking, G. R. ; Sullivan, R. C. ; Petters, M. D. ; Tobo, Y. ; Niemand, M. ; Möhler, O. ; Snider, J. R. ; Wang, Z. ; et al ( January 2015 , Atmospheric Chemistry and Physics)

   Data from both laboratory studies and atmospheric measurements are used to develop an empirical parameterization for the immersion freezing activity of natural mineral dust particles. Measurements made with the Colorado State University (CSU) continuous flow diffusion chamber (CFDC) when processing mineral dust aerosols at a nominal 105% relative humidity with respect to water (RH_w) are taken as a measure of the immersion freezing nucleation activity of particles. Ice active frozen fractions vs. temperature for dusts representative of Saharan and Asian desert sources were consistent with similar measurements in atmospheric dust plumes for a limited set of comparisons available. The parameterizationmore »developed follows the form of one suggested previously for atmospheric particles of non-specific composition in quantifying ice nucleating particle concentrations as functions of temperature and the total number concentration of particles larger than 0.5 μm diameter. Such an approach does not explicitly account for surface area and time dependencies for ice nucleation, but sufficiently encapsulates the activation properties for potential use in regional and global modeling simulations, and possible application in developing remote sensing retrievals for ice nucleating particles. A calibration factor is introduced to account for the apparent underestimate (by approximately 3, on average) of the immersion freezing fraction of mineral dust particles for CSU CFDC data processed at an RH_w of 105% vs. maximum fractions active at higher RH_w. Instrumental factors that affect activation behavior vs. RH_w in CFDC instruments remain to be fully explored in future studies. Nevertheless, the use of this calibration factor is supported by comparison to ice activation data obtained for the same aerosols from Aerosol Interactions and Dynamics of the Atmosphere (AIDA) expansion chamber cloud parcel experiments. Further comparison of the new parameterization, including calibration correction, to predictions of the immersion freezing surface active site density parameterization for mineral dust particles, developed separately from AIDA experimental data alone, shows excellent agreement for data collected in a descent through a Saharan aerosol layer. These studies support the utility of laboratory measurements to obtain atmospherically relevant data on the ice nucleation properties of dust and other particle types, and suggest the suitability of considering all mineral dust as a single type of ice nucleating particle as a useful first-order approximation in numerical modeling investigations.« less
5. A biogenic secondary organic aerosol source of cirrus ice nucleating particles

   https://doi.org/10.1038/s41467-020-18424-6  

   Wolf, Martin J. ; Zhang, Yue ; Zawadowicz, Maria A. ; Goodell, Megan ; Froyd, Karl ; Freney, Evelyn ; Sellegri, Karine ; Rösch, Michael ; Cui, Tianqu ; Winter, Margaux ; et al ( December 2020 , Nature Communications)

   Abstract Atmospheric ice nucleating particles (INPs) influence global climate by altering cloud formation, lifetime, and precipitation efficiency. The role of secondary organic aerosol (SOA) material as a source of INPs in the ambient atmosphere has not been well defined. Here, we demonstrate the potential for biogenic SOA to activate as depositional INPs in the upper troposphere by combining field measurements with laboratory experiments. Ambient INPs were measured in a remote mountaintop location at –46 °C and an ice supersaturation of 30% with concentrations ranging from 0.1 to 70 L –1 . Concentrations of depositional INPs were positively correlated with the mass fractionsmore »and loadings of isoprene-derived secondary organic aerosols. Compositional analysis of ice residuals showed that ambient particles with isoprene-derived SOA material can act as depositional ice nuclei. Laboratory experiments further demonstrated the ability of isoprene-derived SOA to nucleate ice under a range of atmospheric conditions. We further show that ambient concentrations of isoprene-derived SOA can be competitive with other INP sources. This demonstrates that isoprene and potentially other biogenically-derived SOA materials could influence cirrus formation and properties.« less