To investigate evaporation of polar stratospheric clouds (PSCs), mixed nitric-acid/ice films with varying HNO3 content were heated at 0.3 K min-1 in vacuum and monitored with transmission Fourier transform infrared (FTIR) spectroscopy. The ability for HNO3 inclusions to hinder ice evaporation was found to depend on the concentration of HNO3. Specifically, films with initial compositions of ~80:1 and ~150:1 H2O:HNO3 evaporated ~8 K and ~3 K higher than pure ice, respectively. In addition, the surface coverage of nitric acid trihydrate (NAT) appears to control the overall evaporation rate. In the atmosphere, NAT may form on the surface of an ice PSC by direct HNO3 adsorption or by evaporation of a PSC with HNO3 in the bulk. ¿ American Geophysical Union 1996