" Filter replacement indicator Powerful 5-layer air purification system: Pre-filter + Activated carbon + True HEPA + UV/TIO2 photocatalyst + Negative ion Remote control optional Natural scent brings you the romantic feeling(Optional) Convenient installation: Install on the top of bus or truck, installation accessories included, stable and safe. Elegant design: Designed according to the international bus structure, with streamline appearance and good color match. The strong power system circles the air in the bus for 4-6times/hour. "