First step : Pre-filter Infiltrate the Pre-filter with natural antibacterial, anti-allergy elements, can effectively restrain the allergen like pollen. , Function : can effectively restrain the allergen like pollen. Second step : HEPA filter, High efficiency HEPA filter is specially focused on particle with dia. Bigger than 0.25 micron. Third step : activated carbon filter, Can absorb volatile organic compounds and further remove toxic substances such as formaldehyde and other peculiar smell, Fourth step : Air Ionizer, Anion generator can produce negative ions, make the dust, bacteria, spores, pollen, dander and other particles charged, then it will be absorbed by integrated discharge device, it can remove PM2.5. And anion can also activate oxygen molecules in the air to from negative oxygen ion, help human to get fresh air.