FTIR STUDIES ON LIFETIME PROLONGATION OF STRATOSPHERIC ICE PARTICLES DUE TO NAT COATING

Fourier Transform Infra-Red (FTIR) analysis of thin ice films was perf ormed in order to investigate the influence of Nitric Acid Trihydrate (NAT) coating on the life time of stratospheric ice particles in air s ubsaturated with respect to ice. Two sorts of experiments were perform ed in which NAT was either condensed from the gas phase onto preexisti ng ice films or was incorporated into growing ice films, which subsequ ently were subject to slow evaporation under controlled vapor pressure conditions. Neither a thermodynamically efficient sealing of the ice nor a significant kinetic slowing of its evaporation was observed. A p ossible alternative mechanism leading to a more efficient NAT coating is proposed.