Cello DUET Air Purifier is a CARB certified 2-in-1 air purifier with both HEPA H13 filter and Negative Ionizer of 5 million ions. It also have 3 stage filters including pre-filter to extend the life span of HEPA filter, H13 HEPA filter to trap contagious particulates, and active carbon filter to remove odor. It is suitable for classrooms and offices and any gathering area of about 1000 sq. ft. It includes air environment indicator light to show the air quality from blue (good), green (fair), to red (bad). It also includes a sleek touch panel for all kinds of control and provides a smart timer for any timed operation.