| To assess the total human health risks associated with human exposure to ultrafine particle (UFP), the concentrations and fates of UFPs in the in-cabin atmospheres must be understood. In order to assess human exposure more accurately and further prevent adverse health effects from UFP exposure in the in-cabins, it is essential to gain insight into UFP transport dynamics between in-cabin and outside atmospheres and the factors that are able to affect them.;In this dissertation, mathematical model are developed and formulated as tools to improve the understanding of UFP dynamics in the in-cabin atmosphere. Under three different ventilation conditions, (i) Fan off-recirculation (RC) off, (ii) Fan on-RC off, and (iii) Fan on-RC on, the average modeled UFP I/O ratios were found to be 0.40, 0.25 and 0.10, respectively, and agree with the experimental data very well. Then, analysis focused on how the factors, such as ventilation settings, vehicle speed, filtration, penetration, and deposition, affect I/O ratios in broader categories of vehicle cabin microenvironments. Ventilation is the only mechanical process of exchanging air between the in-cabin and the outside. Under condition (ii), I/O ratio that varies from 0.2 to 0.7 was proportional to the airflow rate in the range of 0-360 m3/h. Under condition (iii), the modeled I/O ratio was inversely proportional to the airflow rate from mechanical ventilation within the range of 0.15-0.45 depending on the particle size. Significant variability of the penetration factor (5∼20%) was found due to the pressure difference. A coefficient "B" was successfully introduced to account for the electric charge effect on penetration factors. The effect of penetration on the I/O ratio was then evaluated by substituting penetration factor into the model. Under condition (i), the modeled I/O ratios increased linearly, up to ∼20%, within the penetration factor range. Under condition (iii), the effect of penetration factor is less but still significant (∼10%). The most penetrating particle size was observed at ∼300 nm, where the filtration efficiency was ∼20% in this study. As the filter face velocity (0.1 m s-1 ∼ 0.5 m s-1) increased, filtration efficiency reductions were 10%-20%. As filter usage is increased, filtration efficiency enhancements were 5%-15% but mechanical airflow rate decreased ∼10%. Due to the discrepancy of filtration efficiencies, the UFP I/O ratios changes 5%-15% under condition (ii), and ∼5% under condition (iii). Vehicle speed directly affects the differential pressure between the ambient and the in-cabin environments, which determines the leakage flow rate. When there is no mechanical air supply from outside, in the vehicle (conditions (i) and (iii)), driving speed plays an important role for the air exchange resulting in a greater effect (∼8%). Under condition (ii), vehicle speed has a little effect on the I/O ratios (<5%). |
