Relative Contribution of Outdoor and Indoor Particle Sources to Indoor Concentrations

TLDR

Real‑time indoor and outdoor particle size distribution data collected in four Boston homes in 1996 revealed that indoor sources and time‑activity patterns are key to understanding indoor particle size distributions and concentrations. A simple physical model was applied to estimate source emission, infiltration, and decay rates for specific particle sizes. Cooking, cleaning, and indoor work increased PM(0.7–10 µm) concentrations by 0.27, 0.27, and 0.25 µm³ cm⁻³ min⁻¹, respectively; cooking was the only activity linked to particles <0.5 µm, and outdoor particles contributed significantly to indoor levels with penetration efficiencies ranging 0.38–0.94 for 0.02–0.5 µm and 0.12–0.53 for 0.7–10 µm, while larger particles showed decreasing estimates due to deposition losses.

Abstract

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 μm3 cm-3 min-1, respectively. Cooking was the only variable significantly associated with generation of particles less than 0.5 μm in diameter. Outdoor particles (0.02−0.5 and 0.7−10 μm) were found to contribute significantly to indoor particle levels. Effective penetration efficiencies ranged from 0.38 to 0.94 for 0.02−0.5 μm particles and from 0.12 to 0.53 for 0.7−10 μm particles. Estimates for 0.7−10 μm 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.