Long-term characterization of indoor and outdoor ultrafine particles at a commercial building.

The particle number concentrations in the size range of 10-500 nm were measured inside and outside of a commercial building in Rochester, New York from 2005 to 2009. The indoor ventilation conditions were controlled by a heating, ventilation, and air-conditioning (HVAC) system. The overall average indoor and outdoor particle number concentrations were 2166 cm(-3) and 5214 cm(-3), respectively. Comparison of the indoor and outdoor ultrafine particles (UFP) distributions revealed that indoor sources contributed to the indoor UFP concentrations. The indoor/outdoor (I/O) ratio generally increased with particle size. The I/O ratios in the summer months were higher than those in the winter months. Indoor and outdoor correlations of particle concentrations were slightly weaker in warmer months. These results indicated that changes in the air exchange rates (AER) may have affected the correlation between indoor and outdoor UFP number concentrations. Moreover, indoor activities such as food preparation and cleaning may have contributed to the indoor UFP number concentrations.