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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 18
Atmos. Chem. Phys., 17, 11227–11245, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 17, 11227–11245, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 Sep 2017

Research article | 22 Sep 2017

Comparative measurements of ambient atmospheric concentrations of ice nucleating particles using multiple immersion freezing methods and a continuous flow diffusion chamber

Paul J. DeMott1, Thomas C. J. Hill1, Markus D. Petters2, Allan K. Bertram3, Yutaka Tobo4,5, Ryan H. Mason3, Kaitlyn J. Suski1,a, Christina S. McCluskey1, Ezra J. T. Levin1, Gregory P. Schill1, Yvonne Boose6, Anne Marie Rauker1, Anna J. Miller7, Jake Zaragoza1,b, Katherine Rocci8, Nicholas E. Rothfuss2, Hans P. Taylor2, John D. Hader2, Cedric Chou3, J. Alex Huffman9, Ulrich Pöschl10, Anthony J. Prenni11, and Sonia M. Kreidenweis1 Paul J. DeMott et al.
  • 1Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523, USA
  • 2Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695, USA
  • 3Department of Chemistry, University of British Columbia, Vancouver, BC, V6T1Z1, Canada
  • 4National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
  • 5Department of Polar Science, School of Multidisciplinary Sciences, SOKENDAI (The Graduate School for Advanced Studies), Tachikawa, Tokyo 190-8518, Japan
  • 6Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research (IMK-IFU), 82467 Garmisch-Partenkirchen, Germany
  • 7Department of Chemistry, Reed College, Portland, OR 97202, USA
  • 8Department of Earth Sciences, University of New Hampshire, Durham, NH 03824, USA
  • 9Department of Chemistry & Biochemistry, University of Denver, Denver, CO 80210, USA
  • 10Department of Multiphase Chemistry, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 11National Park Service, Air Resources Division, Lakewood, CO 80228, USA
  • anow at: Pacific Northwest National Laboratory, Richland, WA 99352, USA
  • bnow at: Air Resource Specialists, Fort Collins, CO 80525, USA

Abstract. A number of new measurement methods for ice nucleating particles (INPs) have been introduced in recent years, and it is important to address how these methods compare. Laboratory comparisons of instruments sampling major INP types are common, but few comparisons have occurred for ambient aerosol measurements exploring the utility, consistency and complementarity of different methods to cover the large dynamic range of INP concentrations that exists in the atmosphere. In this study, we assess the comparability of four offline immersion freezing measurement methods (Colorado State University ice spectrometer, IS; North Carolina State University cold stage, CS; National Institute for Polar Research Cryogenic Refrigerator Applied to Freezing Test, CRAFT; University of British Columbia micro-orifice uniform deposit impactor–droplet freezing technique, MOUDI-DFT) and an online method (continuous flow diffusion chamber, CFDC) used in a manner deemed to promote/maximize immersion freezing, for the detection of INPs in ambient aerosols at different locations and in different sampling scenarios. We also investigated the comparability of different aerosol collection methods used with offline immersion freezing instruments. Excellent agreement between all methods could be obtained for several cases of co-sampling with perfect temporal overlap. Even for sampling periods that were not fully equivalent, the deviations between atmospheric INP number concentrations measured with different methods were mostly less than 1 order of magnitude. In some cases, however, the deviations were larger and not explicable without sampling and measurement artifacts. Overall, the immersion freezing methods seem to effectively capture INPs that activate as single particles in the modestly supercooled temperature regime (> −20 °C), although more comparisons are needed in this temperature regime that is difficult to access with online methods. Relative to the CFDC method, three immersion freezing methods that disperse particles into a bulk liquid (IS, CS, CRAFT) exhibit a positive bias in measured INP number concentrations below −20 °C, increasing with decreasing temperature. This bias was present but much less pronounced for a method that condenses separate water droplets onto limited numbers of particles prior to cooling and freezing (MOUDI-DFT). Potential reasons for the observed differences are discussed, and further investigations proposed to elucidate the role of all factors involved.

Publications Copernicus
Short summary
The consistency and complementarity of different methods for measuring the numbers of particles capable of forming ice in clouds are examined in the atmosphere. Four methods for collecting particles for later (offline) freezing studies are compared to a common instantaneous method. Results support very good agreement in many cases but also biases that require further research. Present capabilities and uncertainties for obtaining global data on these climate-relevant aerosols are thus defined.
The consistency and complementarity of different methods for measuring the numbers of particles...
Final-revised paper