NaCl Crust Architecture and Its Impact on Evaporation: Three-Dimensional Insights

Salt precipitation over porous media due to evaporation is known to affect various important processes, including evaporation itself. Many studies have shown that salt crust precipitation reduces evaporation rate, and it has been suggested that the crust constitutes a barrier to vapor flow. Nevertheless, it remains unclear how a porous medium such as the salt crust does not enable upward liquid water transfer by capillary flow. Herein, we show by various imaging methods that the salt crust grows out of specific nucleation centers, to create an elevated crust approximately 1 mm above the matrix surface, most of which is disconnected from the matrix. This indicates that evaporation from a porous medium that is covered by NaCl efflorescence salt crust may occur below the crust, at the soil surface.