The Horizontal Ice Nucleation Chamber HINC: INP measurements at Conditions Relevant for Mixed-Phase Clouds at the High Altitude Research Station Jungfraujoch

Abstract

<p><strong>Abstract.</strong> In this work we describe the Horizontal Ice Nucleation Chamber, HINC as a new instrument to measure ambient ice nucleating particle (INP) concentrations for conditions relevant to mixed-phase clouds. Laboratory verification and validation experiments confirm accuracy of the thermodynamic conditions of temperature (T) and relative humidity (RH) in HINC with uncertainties in temperature of ±0.4 K and in RH with respect to water (RH<sub>w</sub>) of ±1.5 %, which translates to an uncertainty in RH with respect to ice (RH<sub>i</sub>) of ±3.0 % at T > 235 K. For further validation of HINC as a field instrument, two measurement campaigns were conducted in winters 2015 and 2016 at the High Altitude Research Station Jungfraujoch (JFJ; Switzerland, 3580 m a.s.l.) to sample ambient INPs. During winters 2015 and 2016 the site encountered free tropospheric conditions 92 % and 79 % of the time respectively. We measured INP concentrations at 242 K at water sub-saturated conditions (RH<sub>w</sub> = 94 %), relevant for the formation of ice clouds, and in the water supersaturated regime (RH<sub>w</sub> = 103–104 %) to represent ice formation occurring under mixed-phase cloud conditions. In winter 2015 and 2016 the median INP concentrations at RH<sub>w</sub> = 94 % was below the minimum detectable concentration. At RH<sub>w</sub> = 104 %, INP concentrations were an order of magnitude higher, with median concentrations in winter 2015 of 2.8 per standard liter (stdL<sup>−1</sup>; normalized to standard temperature T = 273 K and pressure p = 1013 hPa) and 4.7 stdL<sup>−1</sup> in winter 2016. The measurements are in agreement with previous winter measurements obtained with the Portable Ice Nucleation Chamber, PINC, of 2.2 stdL<sup>−1</sup> at the same location. During winter 2015, two events caused the INP concentrations at RH<sub>w</sub> = 103–104 % to significantly increase above the campaign average. First, an increase to 72.1 stdL<sup>−1</sup> was measured during an event influenced by marine air, coming from the Northern Sea and the Norwegian Sea. Second, INP concentrations up to 146.2 stdL<sup>−1</sup> were observed during a Saharan dust event. To our knowledge this is the first time that a clear enrichment in ambient INP concentration is observed during a time of marine air mass influence, indicating the importance of marine particles on ice nucleation in the free troposphere.</p>

Answer to RC2

“…can selectively be switched on or off and HINCNE used here is identical to the chamber described in Lacher et al (2017), i.e. not making use of the evaporation section and as such, identical to HINCST.…”

“…in 5 K steps. HINC is a continuous flow diffusion chamber (Rogers, 1988;Rogers et al, 1998), based on the design of the UT-CFDC (University of Toronto Continuous Diffusion Chamber; Kanji and Abbatt, 2009) and is described in detail by Lacher et al (2017). Briefly, two parallel, horizontally oriented copper plates separated by a 20 mm polyviniylidene fluoride (PVDF;…”

“…Cloud particles can be formed within the chamber by exposing the injected aerosol particles to RH conditions RH i > 100 %, where the subscript i denotes evaluation with respect to ice. Freezing experiments with salt particles have been performed and compared to theoretical predictions from the water activity based homogeneous freezing parametrization of solution droplets (Koop et al, 2000) to verify chamber performance (Lacher et al, 2017). The flow in HINC is maintained by two mass flow controllers (MFC, G-Series, MKS Instruments, Andover, USA), which control the sheath air and total flow.…”

Answer to RC2

“…In many field measurements CFDCs have been used for measurements of INP concentration at water-supersaturated conditions (e.g., DeMott et al, 2010DeMott et al, , 2016Tobo et al, 2013;Boose et al, 2016;Lacher et al, 2017) and are sometimes used to represent immersion freezing (e.g., DeMott et al, 2017). As water-supersaturated conditions in CFDCs should result in droplet formation followed by freezing at a constant temperature, CFDCs should simulate condensation freezing (see, e.g., Welti et al, 2014, for a discussion of possible condensation freezing mechanisms).…”

“…Ice crystal formation in the atmosphere changes cloud physical and optical properties, thus influencing the lifetime of clouds, and is important for precipitation formation (e.g., Lohmann and Feichter, 2005;Boucher et al, 2013;Mülmenstädt et al, 2015). The importance of ice nucleation mechanisms and the properties of aerosol particles acting as socalled ice-nucleating particles (INPs), which are seed particles necessary for ice nucleation to occur on, are not suffi-Published by Copernicus Publications on behalf of the European Geosciences Union.…”