What is the difference between “oxidation” and “three-ways’ converters?

Oxidation converters control two pollutants – carbon monoxide and hydrocarbons. These are reduced to harmless water vapor and carbon dioxide through accelerated oxidization as the gases pass through the converter. Three-ways converters carry out the same function and, in addition, are designed to reduce levels of nitrogen oxides. They may also include an Air Injection tube which assists the chemical reaction in the oxidization catalyst.