The effects of proximity, compartments, and resuspension on personal exposure to indoor particulate matter

People spend most of their time indoors, but personal exposure to PM is higher than what is predicted by indoor PM levels. This phenomenon is called the “personal cloud”. Three hypotheses for the personal cloud were investigated: the proximity effect, the compartment effect, and the resuspension effect. All three hypotheses are based on the finding that the uniformly mixed assumption is not valid during and immediately after a source is emitted indoors. To provide adequate temporal resolution for this investigation, experiments were performed using a combination of real-time monitors and integrated filter samples.; Proximity effect. The proximity effect was characterized by a series of high concentration, short-duration peaks measured by the real-time monitors while the source was emitting. The mean, median, and variability of these peaks were higher closer to the source. A source proximity effect was measured within 2.0 m from the source for tracer gas sources and 1.0 m for the particle source.; Compartment effect. Under natural ventilation conditions, an internal door was found to effectively limit the transport of indoor emissions from room to room in a residence only for door openings smaller than 5 cm.; Resuspension effect. The resuspension of particles due to the mechanical motion of human activities produced a measurable personal cloud. Five-hour personal exposures during periods of prescribed human activities were 1.4 and 1.6 times as high as indoor concentrations for PM-2.5 for PM-5, respectively. The personal cloud was more pronounced for larger particles.; Results from two independent models showed that during human activity periods nearly all the indoor PM was from resuspended house dust. On days with more typical activity levels, approximately 55 percent of the indoor PM-5 was due to human activities. First estimates of source strengths were calculated for a variety of human activities, which ranged between 0.03 and 0.5 mg min−1 for PM-2.5 and between 0.1 and 1.4 mg min −1 for PM-5. Vacuuming generated a larger percentage of fine particles than activities such as walking around and sitting on furniture, and activity on carpets resuspended more particles than activity on wood floors.