After the participant completed the questionnaire, the researcher somehow installed the monitoring device to monitor levels of PM2.5 under each of five conditions. Air quality in each vehicle was monitored using a TSI Dustrak aerosol monitor (TSI Inc., Shoreview, MN). The Dustrak was used with a 2.5-micron impactor to measure PM2.5 and was calibrated prior to each experimental session with an high efficiency particulate air filter according to the manufacturer’s specifications. The Dustrak was set to record the average PM2.5 concentration every 60 s. A customized calibration factor of 0.32 was applied to the device, determined by calibrating the device in the present study with other light-scattering photometers measuring TSP (Hyland, Travers, & Repace, 2004; Repace, 2004; Travers et al., 2004, 2007).

Two other devices were placed in the car to monitor air quality parameters (e.g., carbon monoxide), but those data are not included in this analysis. Monitoring was conducted on one car at a time. The monitor was secured in the participant’s car (Figure 1). The location and height of the monitoring device inlet was designed to be at head level for a young child sitting in a car seat in the middle of the back seat of each car so that the data collected would provide a reasonable estimate of exposure levels of PM2.5 for a young child sitting in the back seat of the car. Figure 1. Photo of equipment setup inside a participant’s car. Once the equipment was secure, the participant received specific instructions about the setup of the car.

Table 1 presents the specific instructions that were given to each participant for each condition. The participant then sat in the driver’s seat and closed the door immediately. The participant was instructed not to turn on the car, open any windows or doors while inside the car, or turn on the air conditioning or fan, unless specified by the condition (i.e., Condition 5). Table 1. Descriptive summary of conditions Once in the car, the participant lit the cigarette and smoked it at a natural pace. The participant then either finished the cigarette and immediately left the vehicle or drove for 20 min while consuming the cigarette before returning and exiting the vehicle. In all cases, the time from the door opening to the door shutting again during the exit period was less than 3 s and did not appear to affect the levels of PM2.

5 in the car. During each condition, the participant smoked only one cigarette. The start and end times for each cigarette consumed were recorded by the experimenter. The air monitoring device remained in the car for at least 25 min following participant entry into the car to provide baseline comparison values before the car was started, and once the engine was started but Batimastat before the cigarette was lit.