Air filtration in buildings – a potential technique for protecting occupants against fine particles from outdoor sources

Abstract

People spend almost 90% of their time indoors. Thus, the supply air filtration in buildings plays an important role in the occupant exposure to fine particles of outdoor origin. Besides supply air filtration, room air cleaner is a potential measure for reducing the health risks of urban air fine particles. The primary aim of the study was to investigate the role of air filtration when protecting occupants against fine particles from outdoor sources. Efforts were also put to improve the efficiency of supply air filtration, and to clarify the feasibility of room air cleaners. Long-term measurements were made in three locations in urban and suburban environments (school building, apartment in multistorey building, and single-family house). Sophisticated aerosol instruments together with an automatic sampling system were used to measure indoor and outdoor aerosol concentrations and size distributions (size range 0.01 – 10 mm). The results were used to determine the efficiency of air filters and indoor/outdoor (I/O) ratios for fine particles of outdoor origin. The efficiency of supply air filtration can be easily improved up to 90%, and the I/O ratio can be significantly reduced, when compared to existing practices. The uncontrolled leakage air flows in buildings, however, limit the feasibility of supply air filtration, i.e. the achieved I/O ratios (particle size 0.3 mm) were in the range of 0.2-0.3. By using room air cleaners in combination with effective supply air filtration, the I/O ratio could be further reduced, in favorable conditions even below 0.1. The concentration of indoor fine particles originating from outdoors can be effectively reduced by improving the level of supply air filtration. This requires, however, that the uncontrolled leakage air flows are negligible compared with the supply air flow. Room air cleaner, with adequate capacity and acceptable noise level, is another potential option for reducing the occupant exposure to fine particles.