SPECTRAL MEASUREMENTS OF HCL IN THE PLUME OF THE ANTARCTIC VOLCANO MOUNT-EREBUS

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 degrees S, 167.2 degrees E, height 3794m). Fourier transform spectrometer (FTS) measurements were therefore possible fro m the Arrival Heights laboratory (77.8 degrees S, 166.7 degrees E), lo cated approximately 30km south of the volcano. FTS scans were made wit h the interferometer looking upwind and downwind of the summit, result ing in spectra of HCl which showed large column enhancements of the ga s when the sun was viewed through the volcanic plume. Pressure broaden ed spectra confirm that this enhancement was due to an additional trop ospheric component in the column. Assumptions have been made of the pl ume 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 me asurements using other techniques. The result suggests that for this q uiescent type of emission from the volcano there is no evidence of rap id tropospheric scavenging of HCl, as might be expected for more explo sive events and a less dry atmosphere.