[ACC39-05] Direct observation of quasi-liquid layers on ice surfaces by advanced optical microscopy: Effect of nitric acid gas
Keywords:Ice, quasi-liquid layer, nitric acid gas, optical microscopy
Ice is one of the most abundant crystals on the earth, and hence the molecular-level understanding of ice crystal surfaces holds the key to unlocking the secrets of a number of fields. We and Olympus Engineering Co., Ltd. have developed laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM), by which we succeeded in the direct visualization of 0.37-nm-thick elementary steps on ice for the first time [1]. In addition, we could also visualize the quasi-liquid layers (QLLs) on ice crystal surfaces [2], which are covered with thin liquid layers even below the melting point (0°C). The direct observations of QLLs under nitrogen gas revealed the appearance temperatures and partial pressure of water vapor [3,4]. On the other hand, we also found that even trace acidic gas induced the stability of QLLs. In this study, we chose HNO3 as a model atmospheric gas, and directly observed the QLLs on ice basal faces by advanced optical microscopy[5]. Because PHNO3 in the troposphere shows considerable variations (e.g., ranging from ~10-6 Pa in clean air to ~10-2 Pa in polluted urban air [6,7]), the observations in this study were performed under some PHNO3 conditions (0, 10-4 and 10-2 Pa).
Irrespective of the presence/absence of the HNO3 gas, the pure-QLLs and HNO3-QLLs appeared with increasing temperature and disappeared with decreasing temperature. The shape of pure-/HNO3-QLLs showed spherical dome and the contact angle of them on the ice basal face was ~1°. The appearance temperatures of the pure-/HNO3-QLLs were not so different (-1.9 and -0.5 to -1.8 °C, respectively). Although the disappearance temperature of pure-QLLs (-2.2 °C) was almost same as the appearance temperature, the disappearance temperature of the HNO3-QLLs (-6.4 °C) was significantly lower than the appearance temperature of them under high-PHNO3 condition (10-2 Pa). The large thermal hysteresis between the appearance and disappearance temperatures suggests that the disappearance mechanisms of the pure-/HNO3-QLLs were different. We found that the HNO3-QLLs are not composed of pure water, but rather of aqueous HNO3 solutions, and also that the HNO3-QLL and the ice crystal were in equilibrium.
Recently, we studied the effects of hydrogen chloride gas on the behavior of QLLs (HCl-QLLs) on ice basal faces [8,9]. We found that the HCl-QLLs were also aqueous hydrochloric acid solution, and that the temperature and HCl concentration of the HCl-QLLs were also very close to those of a liquidus line: these results were similar to those found in this study. Therefore, ice crystal surfaces would capture large amount of acidic gas components in the acidic-QLLs.
[1] Sazaki et al. (2010) PNAS 107, 19702.
[2] Sazaki et al. (2012) PNAS 109, 1052.
[3] Asakawa et al. (2015) PNAS 113, 1749.
[4] Murata et al. (2016) PNAS 113, E6741.
[5] Nagashima et al. (2020) Crystals 10, 72.
[6] Goldan et al. (1983) Atmos. Environ. 17, 1355.
[7] Hanke et al. (2003) Atmos. Chem. Phys. 3, 417.
[8] Nagashima et al. (2016) Cryst. Growth Des. 16, 2225.
[9] Nagashima et al. (2018) Cryst. Growth Des. 18, 4117.
The details of this study are shown in our paper [5]. We will present this study from other viewpoints in "A-AS07 Atmospheric Chemistry" and "M-IS23: Growth and dissolution of crystal" sessions.
Irrespective of the presence/absence of the HNO3 gas, the pure-QLLs and HNO3-QLLs appeared with increasing temperature and disappeared with decreasing temperature. The shape of pure-/HNO3-QLLs showed spherical dome and the contact angle of them on the ice basal face was ~1°. The appearance temperatures of the pure-/HNO3-QLLs were not so different (-1.9 and -0.5 to -1.8 °C, respectively). Although the disappearance temperature of pure-QLLs (-2.2 °C) was almost same as the appearance temperature, the disappearance temperature of the HNO3-QLLs (-6.4 °C) was significantly lower than the appearance temperature of them under high-PHNO3 condition (10-2 Pa). The large thermal hysteresis between the appearance and disappearance temperatures suggests that the disappearance mechanisms of the pure-/HNO3-QLLs were different. We found that the HNO3-QLLs are not composed of pure water, but rather of aqueous HNO3 solutions, and also that the HNO3-QLL and the ice crystal were in equilibrium.
Recently, we studied the effects of hydrogen chloride gas on the behavior of QLLs (HCl-QLLs) on ice basal faces [8,9]. We found that the HCl-QLLs were also aqueous hydrochloric acid solution, and that the temperature and HCl concentration of the HCl-QLLs were also very close to those of a liquidus line: these results were similar to those found in this study. Therefore, ice crystal surfaces would capture large amount of acidic gas components in the acidic-QLLs.
[1] Sazaki et al. (2010) PNAS 107, 19702.
[2] Sazaki et al. (2012) PNAS 109, 1052.
[3] Asakawa et al. (2015) PNAS 113, 1749.
[4] Murata et al. (2016) PNAS 113, E6741.
[5] Nagashima et al. (2020) Crystals 10, 72.
[6] Goldan et al. (1983) Atmos. Environ. 17, 1355.
[7] Hanke et al. (2003) Atmos. Chem. Phys. 3, 417.
[8] Nagashima et al. (2016) Cryst. Growth Des. 16, 2225.
[9] Nagashima et al. (2018) Cryst. Growth Des. 18, 4117.
The details of this study are shown in our paper [5]. We will present this study from other viewpoints in "A-AS07 Atmospheric Chemistry" and "M-IS23: Growth and dissolution of crystal" sessions.