Relative contribution of outdoor and indoor particle sources to indoor concentrations

The effect of indoor particle sources on indoor particle size distributions and concentrations was previously investigated using real-time indoor and outdoor particle size distribution data collected in four homes in Boston in 1996. These data demonstrated the importance of indoor sources (i.e., cooking, cleaning, and movement of people) and air exchange rates on observed indoor concentrations. As part of the continued analyses of these data, a simple physical model was used to determine the source emission and infiltration rates for specific particle sizes. Decay rates were also estimated. Cooking, cleaning, and indoor work (characterized by movement of people) significantly increased PM(0.7-10) concentrations by 0.27, 0.27, and 0.25 mu m(3) cm(-3) min(-1), respectively. Cooking was the only variable significantly associated with generation of particles less than 0.5 mu m in diameter. Outdoor particles (0.02-0.5 and 0.7-10 mu m) were found to contribute significantly to indoor particle levels. Effective penetration efficiencies ranged from 0.38 to 0.94 for 0.02-0.5 mu m particles and from 0.12 to 0.53 for 0.7-10 mu m particles. Estimates for 0.7-10 Ccm particles decreased with increasing particle size, reflecting the influence of deposition losses from gravitational settling. The real-time particle size distribution data in conjunction with time-activity information provides valuable information on the origin and fate of indoor particles.