The importance of ionic processes that occur in terrestrial, planetary, and stellar atmospheres is receiving increasing recognition. Actually, ions play important, often crucial, roles in a variety of atmospheric processes throughout the universe, and a strong link with the neutral chemistry is also apparent. In the terrestrial atmosphere, the ionic reactions are most relevant in those transient and fleeting events, e.g., lightning, coronas (in thunderstorm clouds and along power lines), where the local ion density is much higher than in unperturbed air, and the chemical systems are typically far from equilibrium. In such cases, ozone, a key molecule for the terrestrial atmosphere, is also present in high local concentrations; it is formed from O(2) by the same transient event. Accordingly, this review provides a survey of the positive ion chemistry of ozone with several of the most important "atmospheric" species: the reactions, the products, and the importance of the examined processes are discussed also in the light of the local thermodynamic disequilibrium (LTD) approach to the chemistry of transient atmospheric events. In all such studies, mass spectrometry is traditionally, and remains today, the experimental technique of choice. The novel application of mass spectrometry to the study of neutral species (NRMS), highly successful for the preparation and positive detection of long-sought, otherwise inaccessible, short-lived neutrals, makes mass spectrometry the most powerful tool now available for the study of the species and processes that are relevant to atmospheric chemistry. Selected examples of the interlink between the neutral and the ionic chemistry are also illustrated.