Passenger Exposures to Ultrafine Particles and In-cabin Air Quality Control
Ultrafine particles (UFPs, diameter < 100nm) have been a significant health concern because of their adverse health effects. Since UFPs primarily origin from traffic emissions in urban environment, previous research efforts have dedicated to study UFPs in near-freeway and on-freeway environments. Despite improved understanding of UFPs in last two decades, UFPs in the in-cabin environment, whereby passenger exposures occur, has been largely overlooked.
Although modern passenger vehicles are commonly equipped with cabin air filters, in-cabin UFP reduction is low (i.e., 40-60%) in outdoor air (OA) mode and commuting exposure alone can account for a significant level of total daily exposure (i.e., up to 45-50%). Although setting the ventilation system to recirculation (RC) mode can reduce in-cabin UFPs by 80-95%, carbon dioxide (CO2) from the exhaled breath of passengers can quickly accumulate in the passenger cabin.
In order to reduce passenger exposures to UFPs and CO2, this dissertation work investigated the in-cabin environment experimentally and quantitatively. From experimental measurements, this work quantified automotive envelope leakage and ventilation systems across a wide range of vehicle models / types from various manufacturers. The infiltration was found specific to location and also conditionally occurred as a result of two competing pressures: in-cabin pressure and aerodynamic pressure on vehicle envelope. The aerodynamic pressure also changed as a function of driving speed. To extend the findings, this dissertation work developed a quantitative model to simulate in-cabin air quality and evaluated the effects of infiltration and passive ventilation in wide range of driving speed and ventilation conditions. Parametric analysis using the model elucidated the fractional significance of in-cabin UFP gain/loss mechanisms affected by driving speed. Finally, the dissertation work proposed a novel simultaneous control method and demonstrated in-cabin concentration reduction of 93% on average for UFPs in filed conditions while reducing CO2 level by a factor of 3-4.