Impact of Outdoor Particles on Indoor Air

Abstract

Even people mostly stay indoors, they are constantly exposed to outdoor-originated particles. Outdoor particles can penetrate into indoor environments via the building envelope through ventilation and air infiltration. Penetration factor is the ratio of outdoor particles entering the indoor environments through the building’s envelope, and infiltration factor is the equilibrium fraction of ambient particles that enter and remain suspended indoors. The penetration factor and infiltration factor are important parameters to understand the transport of particles from outdoors to indoors. Penetration factors can be measured according to regression approach, equilibrium concentration approach, or error analysis approach. The penetration factors are 0.78 ± 0.17 for accumulation-mode particles (0.1–1 μm diameter). They decreased due to Brownian diffusion for smaller particles, or due to stronger gravitational setting and impaction for larger particles. In addition to particle sizes, penetration factors are determined by pressure differences, geometry and surface roughness of cracks, etc. Infiltration factors can be measured by regression approach, equilibrium concentration approach, or tracer element approach, and can also be simulated based on the air change rate, penetration factor and deposition rate. The infiltration factors of PM2.5 are approximately 0.50, which are lower than ultrafine particles and higher than PM10 under the same conditions. Infiltration factors are also influenced by air change rates, window opening behaviors, ventilation systems, etc.KeywordsParticulate matterIndoor airPenetration factorInfiltration factor