The function of the ionizers in an air purifier is straight forward. It causes the particles of dust and other impurities to bond together with air molecules. These unwanted substance form larger clusters which are removed by the filters of the air purifiers. The simple theory is that bigger particles are easier to filter out.
Gases and vapors are chemical pollutants that affect the health. Filters (such as HEPA Filters) are very good at removing particulate matter in the air. However, they are unable to remove gases and vapors. Gases and vapors are .01 microns or even much smaller in size. This means that these gases and vapors are 30 times smaller than the particles that HEPA filters can catch