Sensory source strength of used ventilation filters

A two-year-old filter was placed in a ventilation system recirculating the air in an experimental space. Via glass tubes supplied with a small fan it was possible to extract air upstream and downstream of the filter to an adjacent room. A panel could thus perform sensory assessments of the air from the experimental space after facial exposure, without entering the space. Alternatively, the panel could enter the space and evaluate the air quality after full exposure to the air. The sensory pollution load of the filter determined from full exposure was approximately 7 times lower than when determined after facial exposure. Even with the lower values of the sensory pollution load found in the present study, model predictions of the perceived air quality in a typical office show that used filters may still be important sources of indoor air pollution.