OBJECTIVES. THE VOLCANIC MOON IO AND ITS ROLE IN THE JUPITER SYSTEM AS A SOURCE OF MATERIAL CONTINUES TO BE ENIGMATIC. IO S TENUOUS ATMOSPHERE (MAINLY S O SO2) IS SOURCED BOTH BY VOLCANIC ACTIVITY AND ALSO SUBLIMATION OF SO2 FROST. VARIABILITY IN THE ATMOSPHERE (TEMPORAL HEMISPHERIC RADIAL COMPOSITIONAL) IS NOT WELL UNDERSTOOD - PRIMARILY DUE TO A LACK OF TEMPORAL COVERAGE OF IO AND THUS UTILIZING DATA DURING THE CASSINI FLYBY EPOCH TO COMPARE WITH EARLIER AND LATER DATA (NAMELY FROM HUBBLE SPACE TELESCOPE AND HISAKI) CAN HELP TO CONSTRAIN THE SOURCES OF VARIABILITY. FURTHERMORE OBSERVING BOTH NEUTRAL EMISSION FEATURES (FROM THE ATMOSPHERE) AND ION EMISSION FEATURES (FROM THE SURROUNDING IO PLASMA TORUS) REVEAL DISTINCTIVE CLUES ABOUT PLASMA INTERACTIONS AND ITS EFFECTS; THE CASSINI DATA ARE UNIQUE IN THIS REGARD.