Experimental and Numerical Study on Fine Particle Penetration through Building Cracks and Windows

Description

Recent epidemiological evidence has shown that ambient particle concentration is very closely associated with cardio-pulmonary morbidity and mortality and even premature death. Most personal exposure to particulate matter occurs indoors. The ambient particles that penetrate indoors most likely contribute to a significant portion of people's total exposure to such particles. From the public health point of view, it is important to distinguish between the contribution of outdoor-origin fine particles that penetrate indoors and that of indoor-generated fine particles.In many metropolitan areas, such as Hong Kong and Beijing, a large number of people live in high-rise residences. Infiltration is a dominant pathway by which ambient air enters such residences. Those particles that penetrate indoors and are less than one micrometer (submicron) in size deserve particular attention. Many epidemiological studies have suggested that submicron particles are more toxic than coarse mode particles. However, very few experimental and numerical studies have investigated the penetration of this size range under practical conditions.In this research, the researchers aim to broaden our understanding of the penetration of submicron particles into residential environments. The important factors that affect such penetration will be identified through the systematic variation of the experimental and numerical parameters. Submicron particle penetration through three cracks with well-defined geometries and real window frames will be measured in a laboratory-scale chamber. In addition to particle sizes, pressure differentials and crack geometries, such parameters of penetration as temperature gradient, surface roughness and airflow unsteadiness will be studied experimentally for the first time. The fluorometric technique and real-time concentration measurement will be used to quantify the effectiveness of infiltration by the penetration coefficient and the ratio of indoor-to-outdoor concentration. This will be the first time that fluorometric analysis applies to measure spatial deposition on cracks.A new numerical model is proposed to solve the mass conservation equation of the particles in the cracks. This will be the first attempt to calculate the penetration by incorporating transient, Brownian diffusion, gravitational settling, surface roughness and temperature effects concurrently.In contrast to all of the previous studies, the researchers seek to understand the physics of the penetration mechanisms under real-life conditions. The model developed can be used to predict the indoor concentrations that can be attributed to outdoor-origin particles. This will be very important in helping policymakers and statutory authorities to review or amend current ambient air standards or policies.