Ultrafine particle infiltration into passenger vehicles. Part II: Model analysis

Experimental studies showed that infiltration and passive ventilation are important air exchange mechanisms inside vehicles but previous mathematical models did not consider either one. In this study, we incorporated infiltration and passive ventilation to advance the existing mathematical models and evaluated how different transport mechanisms affect passenger exposures at increasing speeds. Infiltration was formulated using Bernoulli’s equation and passive ventilation was derived empirically. The new model describes ultrafine particle (UFP) and carbon dioxide (CO₂) transport for a wide range of driving speed under any ventilation conditions. Unlike statistical models, this mathematical model can also provide vehicle-specific and transport mechanism-specific information. The model predictions were in a good agreement with data collected from 10 different vehicle models with an average discrepancy of less than 16% for UFPs and less than 3% for CO₂. Under outdoor air (OA) mode, when the fan is off, the model simulation showed that the infiltration and passive ventilation can substantially increase the UFP I/O (in-cabin/on-road concentrations) ratio from 0.15 at 0 km/h to 0.57 at 130 km/h. At medium fan setting, mechanical ventilation dominates and UFP I/O stays at 0.58 regardless of driving speed. Under recirculation (RC) mode, infiltration increases and the RC-mode filtration only removed 44% and 69% of the infiltrated particles at the lowest and medium fan settings, respectively. Model simulations under OA mode show that infiltration starts to occur above 115 km/h with the lowest fan setting; whereas, medium and higher fan settings prevent infiltration up to 145 km/h.     

Ultrafine particle infiltration into passenger vehicles. Part I: Experimental evidence

Previous studies have reported ultrafine particle (UFP) infiltration to the in-cabin microenvironment; however, no systematic measurements have been conducted showing where and under what conditions infiltration occurs. This study examined the automotive envelope leakage and UFP infiltration. We measured the differential pressures between the cabin and the potential leakage area on the surface of 11 passenger vehicles of different models/makers. To identify location of infiltration, UFP concentrations were concurrently measured inside and outside the vehicles as well as near the rear trunks. This study found that UFP infiltration primarily occurs through the rear trunk leakage under recirculation (RC) mode. Under RC mode, aerodynamic effects of a moving vehicle made the surface pressure on the side doors lower (i.e., exfiltration) than the cabin pressure, but higher (i.e., infiltration) on the rear trunk. The UFP concentrations measured near the rear trunks were 2–9 folds higher than inside vehicles. The magnitude of pressure differences increased at higher driving speeds. Under outdoor air (OA) mode, the infiltration was rarely observed because of the fan-controlled cabin pressurization. These data provide the first experimental evidence showing that UFP infiltration into passenger vehicles is location-specific and driving-speed-dependent.     

Is in-cabin exposure to carbon monoxide and fine particulate matter amplified by the vehicle’s self-pollution potential? Quantifying the rate of exhaust intrusion

In-cabin exposure has increased in recent years due to longer commute and/or prolonged times in cars. The intrusion of the vehicle’s own exhaust into the passenger’s compartment has been recognized as a process that amplifies in-cabin passenger exposure. Quantifying its contribution is hampered by uncertainties associated with its measurement method such as trace tests and the lack of data regarding certain critical physical parameters, particularly those pertaining to air exchange rate (AER) and particulate matter deposition rate (DR). In this study, we present a hybrid methodology combining field measurements with a single-zone mass balance to estimate these parameters as well as the source term that represents vehicle self-pollution. In- and out-vehicle carbon monoxide (CO) and fine particulate matter (PM_2.5) were monitored concurrently in test vehicles under idle and moving conditions using several common ventilation modes. In addition to defining a hybrid methodology to characterize the underlying physical parameters, this study found that vehicle self-pollution can account for approximately 15 and 30% of CO and PM_2.5 exposure experienced by vehicle occupants respectively. Vehicle self-exhaust intrusion may constitute a significant PM exposure route for vehicle-based occupations or commuters with prolonged time in vehicles.     

空调供风质量与客(滚)船舱室空气品质刍议

介绍了影响客(滚)船舱室内空气质量的各种因素,阐述了客(滚)船舱室室内空气品质的定义。通过实测,对三条航线的六艘船舶上不同等级客舱内的空气质量进行了调查分析,明确了影响舱室空气品质的主要因素为空调供风质量,并提出了改善的建议与措施。