Indoor pollutants
Most indoor air pollutants are molecules which have evaporated from indoor sources:
foam padding, glues used in hardboard and plywood construction materials, vinyl wall coverings,
plastics in general, carpeting, carpet padding, copiers (solvents), laser printers (ozone),
blue-printers (amines), housekeeping cleaning agents (organic solvents), food preparation,
cigarette smoke, perfumes, after-shaves, deodorants, soaps and human bodies.

Molecules and small particles from indoor sources are the cause of most indoor air pollution.
Conventional air filters remove neither small particles nor molecules.  Forcing air through HEPA or electrostatic filters removes small particles, but not molecules which are thousands of times smaller than the smallest filterable particles.  Molecules must be subtracted from air in a condensation process called adsorption.