Voyager and Galileo data taken near Io are used to calculate ion and electron energy spectra to study the interaction of Io with its space environment. Ion spectra for energetic protons, helium, oxygen and sulfur are presented for the first time. We find intensities of ions above 100 keV are more than an order of magnitude smaller than their counterparts at Europa. Oxygen ions appear to have net losses as they diffuse inward from Europa far exceeding losses of protons or sulfur ions. Estimates of surface sputtering rates by these particles suggest only a small fraction of the neutral gas supplied by Io comes from this process. Radiation dose rates into the surface are heavily dominated by electrons in less than ~1% of the surface area.