A favourable combination of circumstances on 7 September 1996 allowed tracking of the sun through the plume of the active Antarctic volcano, Mount Erebus (77.5 ¿S, 167.2 ¿E, height 3794m). Fourier transform spectrometer (FTS) measurements were therefore possible from the Arrival Heights laboratory (77.8 ¿S, 166.7 ¿E), located approximately 30km south of the volcano. FTS scans were made with the interferometer looking upwind and downwind of the summit, resulting in spectra of HCl which showed large column enhancements of the gas when the sun was viewed through the volcanic plume. Pressure broadened spectra confirm that this enhancement was due to an additional tropospheric component in the column. Assumptions have been made of the plume dimensions and velocity, and a daily downwind flux of HCl derived. This is compared with the daily average flux emitted at the volcanic crater source during periods of passive outgassing, as derived from measurements using other techniques. The result suggests that for this quiescent type of emission from the volcano there is no evidence of rapid tropospheric scavenging of HCl, as might be expected for more explosive events and a less dry atmosphere. ¿ 1998 American Geophysical Union