Properties of sodium sodium chloride brine on laboratory ice

Abstract

Snow and ice surfaces are ubiquitous in the environment. Heterogeneous reactions on those surfaces are responsible for a wide range of phenomena such as the Antarctic stratospheric ozone hole, depletion of boundary-layer ozone, and deposition of mercury. Little is known about the location of impurities on ice surfaces or how that structure depends upon temperature and time after contamination. Therefore, we investigated microscopic structures created by depositing sodium chloride particles onto laboratory-grown ice below the hydrohalite-water eutectic temperature. As the temperature was increased above the eutectic, sodium chloride solution (brine) formed around the particle and spread across the air-ice interface. Literature indicated that ice crystal grain boundaries are the most thermodynamically stable site for brine; yet, on our time scale (minutes), the brine does not drain down the grain boundary and is instead present on the ice surface. Either the surface energetics of the system differ from expectations or a barrier inhibits the brine from moving down the grain boundary on the observational timescale. The area of the brine was used to relate surface coverage by our contamination mechanism to bulk composition. We find that brine does not fully coat the surface for typical snow properties.