Diesel exhaust emission is a major health concern because of the complex nature of its gaseous content (e.g., NO2, NO, CO, and CO2) and high concentration of particulate matter (PM) less than 2.5？μm which allows for deeper penetration into the human pulmonary system upon inhalation. The aim of this research was to elucidate the potential toxic effects of diesel exhaust on a human pulmonary-based cellular system. Validation of a dynamic direct exposure method for both laboratory (230？hp Volvo truck engine) and field (Volkswagen Passat passenger car) diesel engines, at idle mode, was implemented. Human pulmonary type II epithelial cells (A549) grown on porous membranes were exposed to unmodified diesel exhaust at a low flow rate (37.5？mL/min). In parallel, diesel emission sampling was also conducted using real-time air monitoring techniques. Induced cellular effects were assessed using a range of in vitro cytotoxicity assays (MTS, ATP, and NRU). Reduction of cell viability was observed in a time-dependent manner following 30–60？mins of exposure with NRU as the most sensitive assay. The results suggest that the dynamic direct exposure method has the potential to be implemented for both laboratory- and field-based in vitro toxicity studies of diesel exhaust emissions. 1. Introduction Air pollution is a major concern to human health. Epidemiological studies have shown that air pollution poses the greatest human health risks to the young and elderly and those with chronic cardiovascular disease, asthma, or influenza [1–6]. Air pollution is most prevalent in largely populated urban areas such as cities with high-density traffic that consequently poses a higher risk of adverse health effects. Mobile sources such as motor vehicles are the main contributor to urban air pollution, emitting gases, particulates, and/or mixtures of these into the atmosphere. Motor vehicles such as diesel powered passenger vehicles are gaining popularity over the traditional petrol engines as diesel engines have higher fuel efficiency due to the more complete combustion characteristics of the diesel engine. This combustion process is due to the fuel-oxidiser mixing at higher temperatures than these that would occur with a petrol engine [7]. In addition, diesel engines have less CO2 (carbon dioxide) and CO (carbon monoxide) emission although other pollutants such as NO (nitric oxide) and NO2 (nitrogen dioxide) emissions are higher due to the higher temperature resulting in more bonding between nitrogen (N) and oxygen (O2) atoms. Diesel engines produce up to 100 times more particulate
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