The chemical composition of the middle atmosphere can be strongly influenced by Solar Proton Events (SPEs) and Energetic Electron Precipitation Events (EEPs). These events are sources of odd hydrogen and nitrogen, which both contribute to ozone loss in the middle atmosphere. Due to its long lifetime, significant amounts of odd nitrogen and hydrogen are produced by large particle events in the mesosphere and the upper stratosphere can be transported down into the middleand lower stratosphere during polar winter, where e.g. odd nitrogen is a key species in ozone loss. Thus large particle events can potentially contribute significantly to stratospheric ozone loss. This study uses measurements of the Halogen Occultation Experiment (HALOE) instrument onboard the UARS satellite covering the years 1991 - 2005, to investigate the production of species leading to ozone depletion in the middle atmosphere during more than one solar cycle. Furhter, studies of the production/depletion of other important species (e.g. ozone and HCl) throughout the Mesosphere and Stratosphere are presented and also comparisons with chemistry models have been carried out.