Leipzig Ice Nucleation chamber Comparison (LINC): intercomparison of four online ice nucleation counters

Abstract

Abstract. Ice crystal formation in atmospheric clouds has a strong effect on precipitation, cloud lifetime, cloud radiative properties, and thus the global energy budget. Primary ice formation above 235 K is initiated by nucleation on seed aerosol particles called ice-nucleating particles (INPs). Instruments that measure the ice-nucleating potential of aerosol particles in the atmosphere need to be able to accurately quantify ambient INP concentrations. In the last decade several instruments have been developed to investigate the icenucleating properties of aerosol particles and to measure ambient INP concentrations. Therefore, there is a need for intercomparisons to ensure instrument differences are not interpreted as scientific findings.In this study, we intercompare the results from parallel measurements using four online ice nucleation chambers. Seven different aerosol types are tested including untreated and acid-treated mineral dusts (microcline, which is a K-feldspar, and kaolinite), as well as birch pollen washing waters. Experiments exploring heterogeneous ice nucleation above and below water saturation are performed to cover the whole range of atmospherically relevant thermodynamic conditions that can be investigated with the intercompared chambers. The Leipzig Aerosol Cloud Interaction Simulator (LACIS) and the Portable Immersion Mode Cooling chAmber coupled to the Portable Ice Nucleation Chamber (PIMCA-PINC) performed measurements in the immersion freezing mode. Additionally, two continuous-flow diffusion chambers (CFDCs) PINC and the Spectrometer for Ice Nuclei (SPIN) are used to perform measurements below and just above water saturation, nominally presenting deposition nucleation and condensation freezing.The results of LACIS and PIMCA-PINC agree well over the whole range of measured frozen fractions (FFs) and temperature. In general PINC and SPIN compare well and the observed differences are explained by the ice crystal growth and different residence times in the chamber. To study the mechanisms responsible for the ice nucleation in the four instruments, the FF (from LACIS and PIMCA-PINC) and the activated fraction, AF (from PINC and SPIN), are compared. Measured FFs are on the order of a factor of 3 higher than AFs, but are not consistent for all aerosol types and temperatures investigated. It is shown that measurements from CFDCs cannot be assumed to produce the same results as those instruments exclusively measuring immersion freezing. Instead, the need to apply a scaling factor to CFDCs operating above water saturation has to be considered to allow comparison with immersion freezing devices. Our results provide further awareness of factors such as the importance of dispersion methods and the quality of particle size selection for intercomparing online INP counters.

The Horizontal Ice Nucleation Chamber (HINC): INP measurements at conditions relevant for mixed-phase clouds at the High Altitude Research Station Jungfraujoch

“…The two most likely freezing modes in mixed-phase clouds are immersion and condensation freezing, where the INP initiates the freezing from within a supercooled droplet. At present it is questioned whether there is a physical difference between immersion and condensation freezing (Welti et al, 2014;Wex et al, 2014;Burkert-Kohn et al, 2017) but, as the ice germ should form from the liquid phase in both cases, it is not expected so.…”

Composition of ice particle residuals in mixed phase clouds at Jungfraujoch (Switzerland): Enrichment and depletion of particle groups relative to total aerosol

“…In nature, spontaneous freezing of supersaturated vapour or droplets occurs at temperatures below -38°C and a relative humidity (RH) with respect to ice > ~140 % (Kanji et al, 2017), termed homogeneous ice nucleation (Vali et al, 2015). At higher temperatures, a surface -like a particle surface -can lower the free energy and thereby assist the phase transition to ice 10 when relative humidity allows for this, termed heterogeneous ice nucleation.…”

“…Heterogeneous ice nucleation can occur in different modes; (1) deposition nucleation, (2) immersion freezing, (3) contact freezing and (4) condensation freezing. A detailed description of the different modes are found elsewhere (Vali et al, 2015;Kanji et al, 2017). Mixed phase cloud temperature range between -40°C and 0°C (Storelvmo, 2017), and the ice formation is dominated by heterogeneous nucleation in terms of immersion and contact freezing (Lohmann and Diehl, 2006).…”

“…Ice nucleation ability has been studied off-line and on-line in many laboratory and field experiments (Hoose and Möhler (2012); Kanji et al (2017), and references therein). Offline studies are carried out with filters or substrates for deposition nucleation, condensation or immersion freezing experiments, e.g.…”

“…Online methods use different cloud chambers to quantify INPs, e.g. Möhler et al (2003); Bundke et al (2008); DeMott et al (2015); Grawe et al (2016); Burkert-Kohn et al (2017); Lacher et al (2017), and some of the instruments 20 are portable for in-situ measurements. The results from laboratory work are summarised by Hoose and Möhler (2012) showing ice nucleation efficiency of different particle groups against nucleation temperature.…”