The ambient water vapour and temperature conditions of stratospheric sulphate aerosol particles govern their composition and thereby influence their infrared extinction properties. This causes problems in the use of the infrared aerosol extinction as a tracer because variations in the aerosol composition modify the changes in extinction that may arise from the transport of aerosols. An improved tracer which can be derived from measurements of the infrared aerosol extinction, temperature and water vapour abundance, is the H2SO4 component of aerosols. The application of this tracer to studies of stratospheric transport is demonstrated using data from instruments on the Upper Atmosphere Research Satellite and the results are compared to a contour advection calculation. Copyright 1996 by the American Geophysical Union.
