Abstract
The surfaces of ice crystals near the melting point are covered with thin liquid water layers, called quasi-liquid layers (QLLs), which play crucial roles in various chemical reactions in nature. So far, there have been many spectroscopic studies of such chemical reactions on ice surfaces, however, revealing the effects of atmospheric gases on ice surfaces remains an experimental challenge. In this study, we chose HNO3 as a model atmospheric gas, and directly observed the ice basal faces by advanced optical microscopy under partial pressure of HNO3 (~10−4 Pa), relevant to those found in the atmosphere. We found that droplets (HNO3-QLLs) appeared on ice surfaces at temperatures ranging from −0.9 to −0.2 °C with an increase in temperature, and that they disappeared at temperatures ranging from −0.6 to −1.3 °C with decreasing temperature. We also found that the size of the HNO3-QLLs decreased immediately after we started reducing the temperature. From the changes in size and the liquid–solid phase diagram of the HNO3-H2O binary system, we concluded that the HNO3-QLLs did not consist of pure water, but rather aqueous HNO3 solutions, and that the temperature and HNO3 concentration of the HNO3-QLLs also coincided with those along a liquidus line.
Highlights
Ice is one of the most abundant materials on Earth, it has a profound and diverse influence on the global environment [1]
We first investigated the effects of exposure of the ice surfaces to HNO3 gas on the appearance of quasi-liquid layers (QLLs) on ice basal faces by LCM-DIM (Figure 2)
3 gas, QLLs formed on the ice basal face
Summary
Ice is one of the most abundant materials on Earth, it has a profound and diverse influence on the global environment [1]. Than −2 C, droplet-type and thin-layer-type QLLs, which are 20 and 200 times less fluidic than bulk source ice crystals) To confirm this scenario, nitrogen gas bubbled through pure water was injected water [23], respectively, emerged, in addition to QLLs, so called disordered layers, which appeared at into the chamber at 10 mL/min, and no effect on the lateral growth speed of elementary steps temperatures higher than −90 ◦ C [24]. The ice basal faces were always growing and the condensation of water crystal was attached as a substrate for the heterogeneous nucleation of sample ice crystals for the vapor on the QLLs occurred (no evaporation of the QLLs occurred) continuously during our LCM-DIM observation
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