Riesenfeld, E., Chalupa, D., Gibb, F. R., Oberdo, G., Gelein, R., Morrow, P. E., Utell, M. J., and Frampton, M. W.
Ultrafine particles (UFP) may contribute to the morbidity and mortality associated with exposure to ambient particles, but few data are available on ultrafine particle numbers in indoor air, where susceptible subjects spend most of their time. We measured particle number, UFP size distribution, and total suspended particulate (TSP) mass in three locations: (1) a medical floor in a large tertiary care hospital, (2) outdoor air above a construction site outside the hospital, and (3) an environmental exposure chamber with purification of intake air. Mass and number concentrations were recorded continuously in each location over 70–110 h. Mean ± SD particle (p) numbers were 3.63 ± 1.15 × 103 p/cm[sup 3] in the hospital, 3.05 ± 6.65 × 104 p/cm[sup 3] outside, and 5.86 ± 2.11 × 102 p/cm3 in the environmental chamber. In the hospital, particle number and mass declined during the evening hours when the unit was less active, with the particle number as low as 1.15 × 103 p/cm[sup 3]. Particle numbers peaked (2.78 × 104 p/cm[sup 3]) in the morning hours when activity on the unit was the most intense. "Spikes" in fine particle number were often not accompanied by increases in TSP mass. In the hospital, a distinct population of ultrafine particles (median diameter approximately 23 nm) was observed during the lunch hour, suggesting a change in particle source during this time. Outdoor fine particle numbers above the construction site were highly variable, reaching peaks of greater than 1.7 × 106 p/cm[sup 3]. These data suggest that, in the indoor environment, particle numbers and size distribution vary with intensity and type of local activity, and significant peaks in particle number are not detected with daily averages. Monitoring of particle mass may be an inaccurate measure of exposure to ultrafine particles indoors. [ABSTRACT FROM AUTHOR]