Extinction spectra of H2SO4-HNO3-H2O supercooled ternary solution (STS) aerosol particles, fully covering the mid- and near-infrared region from 750 to 13,000 cm-1 (13.9 to 0.7 ¿m), have been measured in the laboratory using a 75 dm3 volume coolable aerosol cell coupled with a Fourier transform spectrometer. The STS spectra were recorded at temperatures close to those encountered in the polar stratosphere and were fitted to a spectrum modelled by combining Mie scattering theory and published thin film refractive index data. Good agreement between model and laboratory data was found in the region 1300--13,000 cm-1, but significant deviations were found in the region 750--1300 cm-1.