Special issue |
Fifth International Workshop on Ice Nucleation (FIN) (ACP/AMT inter-journal SI)(ACP/AMT inter-journal SI)
Editor(s): Allan Bertram, Martina Krämer, Barbara Ervens, and Daniel Knopf
Special issue jointly organized between Atmospheric Chemistry and Physics and Atmospheric Measurement Techniques
We conducted the Fifth International Workshop on Ice Nucleation (FIN) to (1) understand the microphysics of how particles nucleate ice, (2) determine the number of ice forming particles as a function of atmospheric properties such as temperature and relative humidity, (3) measure the atmospheric distribution of ice forming particles and (4) ascertain the role of anthropogenic activities in producing or changing the behaviour of ice forming particles. To accomplish these goals we held three distinct workshops on the topic of atmospheric ice nucleation. The first was an intercomparison of instruments to determine the composition of ice forming particles in a controlled laboratory setting. This took place in autumn 2014 at the location of the last ice nucleation instrument intercomparison: the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber located at the Karlsruhe Institute of Technology. The second was an intercomparison of instruments used to determine cloud formation conditions. This activity also took place at AIDA and was conducted in spring 2015. Because ice nucleation predominantly takes place at the low temperatures found at high altitude, a critical requirement for the third workshop was a facility that offers access to free-tropospheric air masses with minimal local particle sources. We used the Desert Research Institute’s recently renovated Storm Peak Laboratory for this workshop in autumn 2015.
This study presents a new continuous-flow-diffusion-chamber-style operated ice chamber (Modified Compact Ice Chamber, MCIC) to measure the immersion-freezing efficiency of atmospheric particles. MCIC allowed us to obtain maximum droplet-freezing efficiency at higher time resolution without droplet breakthrough ambiguity. Its evaluation was performed by reproducing published data from the recent ice nucleation workshop and past laboratory data for standard and airborne ice-nucleating particles.
We characterized size-segregated airborne ice-nucleating particles (INPs) during dust storm events in the eastern Mediterranean. We found that particle size can predict its activity, and in general, larger particles are better INPs. The activity of supermicron particles dominated by desert mineral dust was similar between the different dust events regardless of the high variability of the geographic source desert and atmospheric journey.
The composition of airborne dust influences climate and ecosystems but its measurements presents a huge analytical challenge. Using online single-particle mass spectrometry, we demonstrate differences in mineralogy and mixing state can be detected in real time in both laboratory studies and ambient measurements. The results provide insights into the temporal and spatial evolution of dust properties that will be useful for aerosol–cloud interaction studies and dust cycle modelling.
This work investigates the cloud condensation nuclei and ice nucleation activity of bacteria using cloud chamber data and a single particle mass spectrometer. The size and chemical composition of the cloud residuals show that bacterial fragments mixed with agar growth media activate preferentially over intact bacteria cells as cloud condensation nuclei. Intact bacteria cells do not make it into cloud droplets; they thus cannot serve as immersion-mode ice nucleating particles.
Paul J. DeMott, Ottmar Möhler, Daniel J. Cziczo, Naruki Hiranuma, Markus D. Petters, Sarah S. Petters, Franco Belosi, Heinz G. Bingemer, Sarah D. Brooks, Carsten Budke, Monika Burkert-Kohn, Kristen N. Collier, Anja Danielczok, Oliver Eppers, Laura Felgitsch, Sarvesh Garimella, Hinrich Grothe, Paul Herenz, Thomas C. J. Hill, Kristina Höhler, Zamin A. Kanji, Alexei Kiselev, Thomas Koop, Thomas B. Kristensen, Konstantin Krüger, Gourihar Kulkarni, Ezra J. T. Levin, Benjamin J. Murray, Alessia Nicosia, Daniel O'Sullivan, Andreas Peckhaus, Michael J. Polen, Hannah C. Price, Naama Reicher, Daniel A. Rothenberg, Yinon Rudich, Gianni Santachiara, Thea Schiebel, Jann Schrod, Teresa M. Seifried, Frank Stratmann, Ryan C. Sullivan, Kaitlyn J. Suski, Miklós Szakáll, Hans P. Taylor, Romy Ullrich, Jesus Vergara-Temprado, Robert Wagner, Thomas F. Whale, Daniel Weber, André Welti, Theodore W. Wilson, Martin J. Wolf, and Jake Zenker
The ability to measure ice nucleating particles is vital to quantifying their role in affecting clouds and precipitation. Methods for measuring droplet freezing were compared while co-sampling relevant particle types. Measurement correspondence was very good for ice nucleating particles of bacterial and natural soil origin, and somewhat more disparate for those of mineral origin. Results reflect recently improved capabilities and provide direction toward addressing remaining measurement issues.
The detection of low concentrations of ice-nucleating particles (INPs) is challenging. Here we present a new technique (IR-NIPI) that is sensitive to low concentrations of INPs (> 0.01 L−1) and uses an infrared camera with a novel calibration to detect the freezing of experimental suspensions. IR-NIPI temperature measurements prove to be robust with a series of comparisons to thermocouple measurements. Experimental comparisons to other freezing assay instruments are also in agreement.
Ice nucleation commonly studied using droplet freezing measurements suffers from artifacts caused by water impurities or substrate effects. We evaluate a series of substrates and water sources to find methods that reduce the background freezing temperature limit. The best performance was obtained from our new microfluidic device and hydrophobic glass surfaces, using filtered HPLC bottled water. We conclude with recommendations for best practices in droplet freezing experiments and data analysis.