Development and characterization of the Portable Ice Nucleation Chamber 2 (PINCii)

Abstract

Abstract. The Portable Ice Nucleation Chamber 2 (PINCii) is a newly developed continuous flow diffusion chamber (CFDC) for measuring ice nucleating particles (INPs). PINCii is a vertically oriented parallel-plate CFDC that has been engineered to improve upon the limitations of previous generations of CFDCs. This work presents a detailed description of the PINCii instrument and the upgrades that make it unique compared with other operational CFDCs. The PINCii design offers several possibilities for improved INP measurements. Notably, a specific icing procedure results in low background particle counts, which demonstrates the potential for PINCii to measure INPs at low concentrations (<10 L−1). High-spatial-resolution wall-temperature mapping enables the identification of temperature inhomogeneities on the chamber walls. This feature is used to introduce and discuss a new method for analyzing CFDC data based on the most extreme lamina conditions present within the chamber, which represent conditions most likely to trigger ice nucleation. A temperature gradient can be maintained throughout the evaporation section in addition to the main chamber, which enables PINCii to be used to study droplet activation processes or to extend ice crystal growth. A series of both liquid droplet activation and ice nucleation experiments were conducted at temperature and saturation conditions that span the spectrum of PINCii's operational conditions (-50≤ temperature ≤-15 ∘C and 100 ≤ relative humidity with respect to ice ≤160 %) to demonstrate the instrument's capabilities. In addition, typical sources of uncertainty in CFDCs, including particle background, particle loss, and variations in aerosol lamina temperature and relative humidity, are quantified and discussed for PINCii.

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“…At temperatures warmer than required for homogeneous freezing, ice nucleation was not observed below water saturation. Data collected at around 26°C show that all onsets are around droplet breakthrough conditions (gray dashed line), which was experimentally determined for various PINCii operating conditions by Castarède et al (2023). Droplet breakthrough characterizes a threshold in the T-RH i parameter space wherein unfrozen droplets continue to grow to detectable sizes for the OPC, thus inhibiting phase discrimination.…”

“…A strong reduction in EF PN was observed when switching from non-compliant HiS to SECAcompliant LoS, which agrees with other studies that have shown large reductions in particle number emissions Freezing onsets were determined where the frozen fraction between ice crystals (>3 μm) and the total particle number concentrations exceeded 1%. The solid blue line indicates water saturation, the dashed black line represents the homogeneous freezing threshold for 200 nm particles according to Koop et al (2000) (calculated with a water activity (Δa w ) of 0.2946) and the gray dashed line represents the experimentally determined droplet breakthrough conditions of PINCii (Castarède et al, 2023).…”

“…The Portable Ice Nucleation Chamber II (PINCii) is a newly developed continuous flow diffusion chamber (CFDC) built to investigate ice nucleation by aerosol particles (Castarède et al, 2023). During measurements with PINCii, RH ramps for three to four pre-selected lamina temperatures were performed, that is, during each ramping cycle both wall temperatures are continuously adjusted so that the temperature in the sample flow lamina remains constant but the relative humidity with respect to ice (RH i ) is steadily increased.…”

“…Particle counts for size channels 3 and 4, that is, d p > 3 μm, were considered as ice crystals in our results (Castarède et al, 2023). Between transitions to new lamina temperature settings, a solenoid valve at the inlet of PINCii switched to sample HEPA filtered ambient air for 15 min to measure background ice crystal concentrations and to correct values obtained from ramping experiments.…”

“…This can introduce an additional uncertainty when performing measurements at low temperatures. In Castarède et al (2023), the authors show an alternative way to visualize freezing onsets of aerosol particles using PINCii. This approach takes into account the fact that homogeneous freezing is an irreversible process.…”