Behavior of externally mixed liquid and solid polar stratospheric cloud particles in a numerical box model under temperature decrease

Type I polar stratospheric clouds (PSCs) are simulated via an ensemble of externally mixed H_2SO_4/HNO_3/H_2O ternary solution droplets and solid NAT (nitric acid tri-hydrate) particles in a microphysical box model. The behavior of this ensemble is investigated under two temperature-change conditions : meso-and synoptic-scale ones. The results show that the evolution of size and composition of liquid droplets depends strongly on temperature cooling rate, depletion of gas phase HNO_3,and initial size distribution; however, evolution of NAT particles is not strongly influenced by their initial size distribution. The development of the microphysical properties of the particles simulated in the model can be controlled by adjusting such parameters as cooling rate, total number of solid particles, and size distribution. The developed model can be used for interpreting lidar data of Arctic PSC_s, and for simulating PSC particles. It can also be used in photochemical models investigating polar ozone depletion by providing the total surface area of the particles and the changes in gas phase HNO_3 due to condensation (evaporation) on these particles