Fig. 1.
NaCl–water phase diagram in temperature-RHw space. The blue solid curve represents ice saturation (Johari et al., 1994; Koop et al., 2000b) and the pink dash-dotted line represents the DRH extrapolated from measurements at higher temperatures (>278 K) (Tang and Munkelwitz, 1993). Notes: The black dashed line is the homogeneous freezing line from Koop et al.(2000a), for droplets between 1 and 10 μm. The solid and dotted lines 1-5 correspond to experimental trajectories, where the solid portions depict the experimental exposure entering the CFDC main chamber and dashed portions represent the return to ice saturation that occurs within the evaporation section of the CFDC.
Table 1.
Experimental onset temperature ranges for the four salts/salt solutions.
Fig. 2.
NaCl size distributions at different RHw values. The lowest RH condition was obtained in a dry SPIN chamber at 293 K while the others were obtained using an ice-coated chamber with a 235 K laminar flow temperature. Notes: The numbers in the figure indicate the bin numbers.
Fig. 3.
The time evolution of the OPC signal of 4 size channels with three different salts corresponding to the panels. Notes: RH is plotted as a blue dashed line (right y-axis). The red dash-dotted line highlights sharp signal changes, indicating deliquescence onset. In order to separate the data for visualisation, some bin intensities were arithmetically shifted as follows: (a) bin3 + 100, bin6 -50, bin7 -600; (b) bin3 + 100, bin7 -350; (c) bin3 + 100, bin7 − 400.
Fig. 4.
Experimental NaCl particle number concentration as a function of RHw (upper panels), size distributions (middle panels) and particle composition assigned by machine learning (lower panels). Notes: The left column is observations at T = 231 K, while the right column corresponds to T = 237 K.
Fig. 5.
Experimental data from this study in temperature/RHw space. Notes: Deliquescence (plus signs) and ice nucleation (squares and hexagrams) plotted with literature values taken from Wise et al. (2012) (blue triangles), Schill and Tolbert (2014) (black triangles), and Wagner and Möhler (2013) (red triangles). The phase boundaries are reproduced from Fig. 1. A typical error bar for deliquescence is added to the deliquescence onset RH at the lowest temperature, and the error bar is calculated as the standard deviation of the lamina temperature and relative humidity using CFD simulation code developed by Kulkarni and Kok (2012).
Fig. 6.
Experimental data from the present study in ice supersaturation-temperature space. Notes: Observed deliquescence (plus symbols, same colour scheme as Fig. 5), homogenous ice nucleation (black squares) and heterogeneous nucleation (black hexagrams) are indicated. Previously published observations are taken from Schill and Tolbert (2014) (green asterisk), Wise et al. (2012) (blue triangle), Wagner and Möhler (2013) (red triangles), China et al. (2017) (green triangles) and Ladino et al. (2016) (open circles: pure NaCl in red, Sigma-Aldrich sea salt in magenta and Instant Ocean sea salt in black). Black dots represent droplet breakthrough from this study. The phase boundaries are re-plotted from Fig. 1. The coloured shaded areas illustrate the ways in which sea salts may act as cloud seeds: CCNs in purple; CCNs/HFNs in blue; CCNs/HFNs/INPs in yellow. The error bars are calculated as the standard deviation of the lamina temperature and relative humidity using CFD simulation code developed by Kulkarni and Kok (2012).
Fig. 7.
NaCl water phase diagram: solid (S), supercooled metastable liquid 1 (ML1), supersaturated metastable liquid 2 (ML2), liquid (L) and dihydrate (DH).