Air Pollutant Penetration through Airflow Leaks into Buildings

The penetration of ambient air pollutants into the indoor environment is of concern owing to several factors: (1) epidemiological studies have shown a strong association between ambient fine particulate pollution and elevated risk of human mortality; (2) people spend most of their time in indoor environments; and (3) most information about air pollutant concentration is only available from ambient routine monitoring networks. A good understanding of ambient air pollutant transport from source to receptor requires knowledge about pollutant penetration across building envelopes. Therefore, it is essential to gain insight into particle penetration in infiltrating air and the factors that affect it in order to assess human exposure more accurately, and to further prevent adverse human health effects from ambient particulate pollution. In this dissertation, the understanding of air pollutant infiltration across leaks in the building envelope was advanced by performing modeling predictions as well as experimental investigations. The modeling analyses quantified the extent of airborne particle and reactive gas (e.g., ozone) penetration through building cracks and wall cavities using engineering analysis that incorporates existing information on building leakage characteristics, knowledge of pollutant transport processes, as well as pollutant-surface interactions. Particle penetration is primarily governed by particle diameter and by the smallest dimension of the building cracks. Particles of 0.1-1 {micro}m are predicted to have the highest penetration efficiency, nearly unity for crack heights of 0.25 mm or higher, assuming a pressure differential of 4 Pa or greater and a flow path length of 3 cm or less. Supermicron and ultrafine particles (less than 0.1 {micro}m) are readily deposited on crack surfaces by means of gravitational settling and Brownian diffusion, respectively. The fraction of ozone penetration through building leaks could vary widely, depending significantly on its reactivity with the adjacent surfaces, in addition to the crack geometry and pressure difference. Infiltrating air can also travel through wall cavities, where the penetration of particles and ozone is predicted to vary substantially, depending mainly on whether air flow passes through fiberglass insulation. For ozone, its reactivity with the insulation materials is also an important factor. The overall pollutant penetration factor is governed by the flow-weighted average from all air leakage pathways. Large building leaks would strongly influence the overall penetration factor, because they permit much larger flow.