LABORATORY SIMULATION OF POLAR STRATOSPHERIC CLOUDS

A flow cell built to simulate heterogeneous reactions in the stratosph ere is described. Small particles (approximately 1 mum diameter) have been made from nitric acid solutions and distilled water. These have m any of the important physical properties of types I and II polar strat ospheric clouds (PSCs), respectively. The FTIR spectra of the ice part icles are compared with calculated extinction (scattering plus absorpt ion) spectra to obtain an estimate of their size distributions. The av erage particle size can be controlled by varying the flow conditions. The nitric acid particles have not been as well characterized, because the required optical constants are not yet available. Their spectra, however, have the characteristics expected for type I PSCs, and resemb le those previously reported for thin-film nitric acid trihydrate.