Abstract
Abstract. Atmospheric ice-nucleating particles (INPs) play an important role in determining the phase of clouds, which affects their albedo and lifetime. A lack of data on the spatial and temporal variation of INPs around the globe limits our predictive capacity and understanding of clouds containing ice. Automated instrumentation that can robustly measure INP concentrations across the full range of tropospheric temperatures is needed in order to address this knowledge gap. In this study, we demonstrate the functionality and capacity of the new Portable Ice Nucleation Experiment (PINE) to study ice nucleation processes and to measure INP concentrations under conditions pertinent for mixed-phase clouds, with temperatures from about −10 to about −40 ∘C. PINE is a cloud expansion chamber which avoids frost formation on the cold walls and thereby omits frost fragmentation and related background ice signals during the operation. The development, working principle and treatment of data for the PINE instrument is discussed in detail. We present laboratory-based tests where PINE measurements were compared with those from the established AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud chamber. Within experimental uncertainties, PINE agreed with AIDA for homogeneous freezing of pure water droplets and the immersion freezing activity of mineral aerosols. Results from a first field campaign conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) observatory in Oklahoma, USA, from 1 October to 14 November 2019 with the latest PINE design (a commercially available PINE chamber) are also shown, demonstrating PINE's ability to make automated field measurements of INP concentrations at a time resolution of about 8 min with continuous temperature scans for INP measurements between −10 and −30 ∘C. During this field campaign, PINE was continuously operated for 45 d in a fully automated and semi-autonomous way, demonstrating the capability of this new instrument to also be used for longer-term field measurements and INP monitoring activities in observatories.
Highlights
Atmospheric ice-nucleating particles (INPs) induce ice formation in atmospheric clouds and are important for initiating precipitation in mixed-phase clouds and determining the phase of clouds, their albedo, lifetime and other important properties (DeMott et al, 2010)
Refilling causes compression of the chamber air and related warming. This leads to the evaporation of the droplets and ice crystals after some time; the abrupt stop of particle recording is related to the fact that the pump flow rate through the optical particle counter (OPC) is stopped at the end of expansion, so that only a few particles are moving through the OPC detection volume during the refill mode
We present a new instrument called PINE (Portable Ice Nucleation Experiment) for laboratory studies of ice nucleation and field measurement of ice-nucleating particles (INPs)
Summary
Atmospheric ice-nucleating particles (INPs) induce ice formation in atmospheric clouds and are important for initiating precipitation in mixed-phase clouds and determining the phase of clouds, their albedo, lifetime and other important properties (DeMott et al, 2010). Cloud, weather and climate models need to formulate and quantify primary ice formation as accurately as possible (Vergara-Temprado et al, 2018; Waliser et al, 2009) This is achieved by calculating the abundance of INPs with parameterizations based on either laboratory ice-nucleation experiments (Hoose and Möhler, 2012; Murray et al, 2012; Sesartic et al, 2013; Spracklen and Heald, 2014; VergaraTemprado et al, 2018) or field measurements (DeMott et al, 2010; McCluskey et al, 2018; Tobo et al, 2013; Wilson et al, 2015). The instrument is operated in repeated cycles of sampling the aerosol into a pre-cooled cloud chamber, activating the aerosol particles as supercooled droplets and ice crystals by expanding the air inside the cloud chamber and refilling the cloud chamber with fresh aerosol for the cycle (see Sect. 4)
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