In the electret filtration of charged ultrafine particles, Brownian diffusion and Coulombic force are the dominant collection mechanisms. In the present work, the interaction between Brownian diffusion and Coulombic force in electret filtration is studied by solving convective diffusion equation including Coulombic force, and the numerical results are compared with the experimental data. As a result, the dominant region of either Brownian diffusion or Coulombic force is obtained as a function of Peclet number, Pe, and Coulombic force parameter, KC. It is shown that there is a negative interaction between Brownian diffusion and Coulombic force, i.e., Coulombic capture efficiency is reduced with decreasing Pe. These results suggest that Brownian diffusion and Coulombic capture efficiency is not a simple sum of Brownian diffusion efficiency and Coulombic capture efficiency.
Recently, indoor air quality has been affected by a variety of chemicals, which are suspected to be the cause of sick building syndromes. In this study, the concentration of Formaldehyde (FA) in the indoor environments was investigated around our living conditions. The 84 locations were selected from various living environments such as homes, schools, bookstores, and cars in Kanazawa city. FA from 51/84 locations (60.7 %) detected more than 0.02 ppm whereas FA concentrations from 25/84 locations (29.8 %) detected more than 0.04 ppm. The results indicated that we have been exposed to FA on low-level and long-term basis. The guideline of FA concentration recommended by the Ministry of Health, Labour and Welfare Japan is 0.08 ppm. Laboratory experiments were also carried out on building materials (natural and plywood), building adhesive agents, furniture, and cigarette smoke. When heating was carried out in an unventilated room, FA concentration increased with time according to the rise in room temperature. Once ventilation was started FA concentration dropped immediately. FA concentrations in Japanese-style rooms indicated a lower value than that of European-style rooms. FA was emitted from building materials (wall, ceiling, and floor materials with adhesive agents) in both homes and buildings. Our life styles associated with heating-system, furniture and cigarette smoke, are also responsible for the emission of FA.