An extensive set of HI Lyman- α images obtained with the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) from 1997-2001 has been analyzed to provide information about the spatial and temporal character of Io's SO 2 atmosphere. An atmospheric distribution map derived from the observations reveals that the sunlit SO 2 atmosphere is temporally stable on a global scale, with only small local changes. An anti-/sub-jovian asymmetry in the SO 2 distribution is present in all 5 years of the observations. The average daytime atmosphere is densest on the anti-jovian hemisphere in the equatorial regions, with a maximum equatorial column density of 5.0×10 cm at 140° longitude. The SO 2 atmosphere also has greater latitudinal extent on the anti-jovian hemisphere as compared to the sub-jovian. The atmospheric distribution appears to be best correlated with the location of hot spots and known volcanic plumes, although small number statistics for the plumes limits the correlation.