The chemical and physical properties of218Po immediately following its formation from222Rn decay are important in determining its behavior in indoor atmospheres and play a major part in determining its potential health effects. In 88% of the decays, a singly charged, positive ion of218Po is obtained at the end of its recoil path. These ions can interact with water vapor or other volatile organic compounds (VOCs) that may exist in indoor air. The ions can be neutralized by 3 different mechanisms, small-ion recombination, electron transfer, and electron scavenging. In typical indoor air, the ion will be rapidly neutralized by transfer of electrons from lower ionization potential gases such as NO2. The neutral molecule can then become incorporated in ultrafine particles formed by the radiolytic processes in the recoil path. These particles will typically be formed by the presence of the air ions produced by the passage of the emitted -particle through ion-induced nucleation. In addition these energetic ions can react with water molecules to produce hydroxyl radicals. Thus, the decay of the radon nucleus produces a variety of effects and can result in changes in the size of the radioactive species that includes the radon progeny.