Efficiency of a Portable Indoor Air Cleaner in Removing Pollens and Fungal Spores

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Abstract
The purpose of this study was to determine the efficiency of a commercial air cleaner in removing pollens and fungal spores indoors. The effect of the air ventilation rate in a room on the removal efficiency was also investigated. The air cleaner consisted of a HEPA filtration unit and a fan operated at a flow rate of 404 m3 per h. This system was tested in two adjacent but separate bedrooms on the second floor of a single-family home. The system was used in Room A to clean the air; Room B served as a control. The study was conducted during the summer and fall, and an evaporative cooling unit with ducts to each room delivered outside air. The ventilation rate was controlled by adjusting the flow rates of the evaporator with minor adjustment of the window opening to give similar ventilation rates in both rooms. At the beginning of the test, ventilation rates were measured using an SF6 tracer gas method, and ventilation was adjusted so that both rooms had similar air exchange rates. Then an air cleaner unit was turned on in Room A, and aerosol samples were collected every 2 h. Two identical Allergenco Biosamplers (Mark-3, Allergenco, San Antonio, TX) collected particles by impaction on a moving glass slide coated with silicon grease. The test lasted for 24 h. Pollens and fungal spores on the collection substrates were identified and counted using an optical microscope. Particle concentrations were then estimated from the particle count and flow rate. At a high ventilation rate (2.8–3 h−1), the system helped to maintain a low concentration (10–20% of initial concentration) of pollen and spores; particle concentrations in Room B remained the same without the air cleaner. At a moderate ventilation rate (1–1.2 h−1), the nitration process helped to remove >80% of the particles in Room A, whereas in Room B, the concentrations were reduced to about 50% by sedimentation. At a low air exchange rate (−1), pollen and fungal spore concentrations in both rooms decreased rapidly to < 10% of initial values within 1 h, indicating sedimentation of large particles. The air cleaner helped the cleaning process by shortening the cleanup time. Our results suggest that this air cleaner is useful in filtering out pollens and spores, and it is more effective when doors and windows are closed, especially when there are no activities in the room.