Inhalation of particulate matter is known to cause negative human health effects. Consequently, regulatory agencies have set regulations and standards that limit the maximum concentrations to which persons may be exposed and the maximum concentrations allowed in the ambient air. However, these standards consider steady exposure over large spatial and time scales. Because many vehicles' exhaust systems direct exhaust towards sidewalks, pedestrians in close proximity to a roadway may experience events where for brief periods of time particulate matter concentrations are high enough to cause acute health effects. In order to quantify these exposure events, instruments which measure specific exhaust pollutant concentrations were placed near a roadway and connected to the mouth of a mannequin used as a pedestrian surrogate. A representative estimate of the exposure potentially experienced by pedestrians was obtained by measuring concentrations at the mannequin's mouth during drive-by events with a diesel truck and a gasoline truck. Breathing rates were then multiplied by the measured concentrations to determine the mass of pollutant inhaled daily and per breath. The highest concentrations observed with the diesel test vehicle were 2.2 million particles/cc and 1400 mug/m 3. The average concentration of particulate matter measured over the duration of a single drive-by test was observed to reach the same order of magnitude as the low concentrations used in human clinical studies which are known to cause acute health effects. It was also observed that concentrations of particulate matter were 2 to 3 times higher at the height of a stroller than at the mouth of a standing mannequin during heavy acceleration tests. However, for other operating conditions, the opposite of this result was observed. Additionally, particulate concentrations obtained with the diesel vehicle were typically an order of magnitude or more greater than those obtained with the gasoline vehicle. Particulate matter concentrations during drive-by incidents can easily reach or exceed the low concentrations that can cause acute health effects for brief periods of time. For the case of a 2006 diesel fueled Dodge Ram 2500 and a 2001 gasoline fueled Dodge Ram 1500, the mass of particulate matter inhaled during drive-by incidents was small compared to the mass inhaled daily at ambient conditions. On a per breath basis, however, the mass of particulate matter inhaled was large compared to the mass inhaled at ambient conditions. Finally, it was determined that exposure is directly dependent on the location of a pedestrian with respect to the tailpipe of a passing vehicle.
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