DETECTION OF SO2 IN THE UV SPECTRUM OF VENUS

The broad absorption feature below 3300Å in the Venus uv spectrum previously reported by Barker is identified as primarily due to SO2 absorption based on new higher resolution spectra of the 3000‐3400Å region showing broad (10Å), unresolved absorptions in the regions at all SO2 band origins between 3000 and 3300Å. SO2 mixing ratios vary from 5 × 10−7 down to an upper limit of 2 × 10−8 at a phase angle of 138°. Previous observational determinations of the SO2 mixing ratio were biased toward large phase angles, and consequently did not detect any SO2 absorption at the 10−8 level. The upper limit derived from the CS2 band head at 3206Å is ≤ 5 × 10−8. The observed range of SO2 mixing ratios (<2 × 10−8 to 5 × 10−7) is consistent with model predictions based on the sulfur photo‐chemistry at the cloud tops. Ground‐based observations of SO2 mixing ratio will provide constraints on models and check on the Venera and Pioneer Venus measurements of the mixing ratios of SO2 and other sulfur‐bearing gases with altitude. Copyright 1979 by the American Geophysical Union.