Heterogeneous Ice Nucleation Ability of NaCl and Sea Salt Aerosol Particles at Cirrus Temperatures

Abstract

In situ measurements of the composition of heterogeneous cirrus ice cloud residuals have indicated a substantial contribution of sea salt in sampling regions above the ocean. We have investigated the heterogeneous ice nucleation ability of sodium chloride (NaCl) and sea salt aerosol (SSA) particles at cirrus cloud temperatures between 235 and 200 K in the Aerosol Interaction and Dynamics in the Atmosphere aerosol and cloud chamber. Effloresced NaCl particles were found to act as ice nucleating particles in the deposition nucleation mode at temperatures below about 225 K, with freezing onsets in terms of the ice saturation ratio, Sice, between 1.28 and 1.40. Above 225 K, the crystalline NaCl particles deliquesced and nucleated ice homogeneously. The heterogeneous ice nucleation efficiency was rather similar for the two crystalline forms of NaCl (anhydrous NaCl and NaCl dihydrate). Mixed‐phase (solid/liquid) SSA particles were found to act as ice nucleating particles in the immersion freezing mode at temperatures below about 220 K, with freezing onsets in terms of Sice between 1.24 and 1.42. Above 220 K, the SSA particles fully deliquesced and nucleated ice homogeneously. Ice nucleation active surface site densities of the SSA particles were found to be in the range between 1.0 · 1010 and 1.0 · 1011 m−2 at T < 220 K. These values are of the same order of magnitude as ice nucleation active surface site densities recently determined for desert dust, suggesting a potential contribution of SSA particles to low‐temperature heterogeneous ice nucleation in the atmosphere.

Solid Ammonium Nitrate Aerosols as Efficient Ice Nucleating Particles at Cirrus Temperatures

“…Heterogeneous ice formation below the homogeneous freezing limit is observed. A similar transition temperature of around 230 K, where the ice nucleation behavior changes from deliquescence and homogeneous freezing to heterogeneous ice nucleation was observed for sodium chloride (NaCl) and sea salt particles (Schill & Tolbert, 2014; Wagner et al, 2018; Wise et al, 2012). With 61.8% RH w , the room temperature DRH of AN is much lower compared to AS and NaCl (Tang & Munkelwitz, 1993).…”

“…The dashed red lines represent fits to the shifted and unshifted INKA n s curves as computed from equation with = 1.13 and 1.26, respectively. The n s data for the AN particles are compared to the ice nucleation active surface site densities recently determined from AIDA ice nucleation experiments with other aerosol types, including solid desert dust particles (Ullrich et al, 2017), crystalline NaCl and NaCl·2H 2 O particles (Wagner et al, 2018), as well as mixed‐phase solid/liquid sea salt aerosol particles with crystalline NaCl and NaCl·2H 2 O inclusions (Wagner et al, 2018) (black, blue, and green crosses, respectively).…”

“…The experiments were conducted in the AIDA aerosol and cloud chamber, an 84‐m 3 ‐sized aluminum vessel whose static temperature can be controlled between 333 and 183 K (Figure 1) (Möhler et al, 2003; Wagner et al, 2009, 2018). For cleaning purposes, the chamber can be evacuated to a final pressure of about 0.01 hPa.…”

“…Regarding the impact of AN particles on cloud formation and, specifically, on the formation of high‐altitude cirrus clouds involving the nucleation of ice particles, a predominance of the liquid state would only favor cirrus formation via the homogeneous freezing of the aqueous AN solution droplets at elevated humidity levels (Cziczo & Abbatt, 2001; Koop, Luo, et al, 2000; Tabazadeh & Toon, 1998). In contrast, crystalline AS and mixed‐phase (solid/liquid) sea salt aerosol particles were found to be able to act as so‐called ice nucleating particles (INPs) at cirrus conditions (Vali et al, 2015), promoting heterogeneous ice formation at much lower relative humidities compared to homogeneous freezing conditions (Abbatt et al, 2006; Schill & Tolbert, 2014; Wagner et al, 2018).…”

Laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF): performance, reference spectra and classification of atmospheric samples

“…The corresponding size distribution can be plotted as d va histogram, a Gaussian fit of which yields number mean d va values and the standard deviation (width). We also measured mass spectra of non-spherical NH 4 NO 3 (χ = 0.8; Williams et al, 2013) and NaCl particles (cubic, χ = 1.06 to 1.17; Zelenyuk et al, 2006a). Similar to PSL particles, NH 4 NO 3 and NaCl particles show relatively high and stable HR with average values of 80 and 66 % (see panel d in Fig.…”