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 i n 1996. These data demonstrated the importance of indoor sources (i.e., coo king, cleaning, and movement of people) and air exchange rates on observed indoor concentrations. As part of the continued analyses of these data, a s imple physical model was used to determine the source emission and infiltra tion rates for specific particle sizes. Decay rates were also estimated. Co oking, cleaning, and indoor work (characterized by movement of people) sign ificantly 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 significantl y associated with generation of particles less than 0.5 mu m in diameter. O utdoor particles (0.02-0.5 and 0.7-10 mu m) were found to contribute signif icantly to indoor particle levels. Effective penetration efficiencies range d 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 inc reasing particle size, reflecting the influence of deposition losses from g ravitational settling. The real-time particle size distribution data in con junction with time-activity information provides valuable information on th e origin and fate of indoor particles.