Method for Measuring the Ratio of In-Vehicle to Near- Vehicle Exposure Concentrations of Airborne Fine Particles

摘要

Human exposure to fine particulate matter (PM2.5) is causally linked to cardiovascular andpulmonary diseases. In-vehicle exposure may account for 10 to 20 percent of daily averageexposure. However, exposure models are typically based on area-wide air quality data thatpoorly predict in-vehicle concentration. A practical method is demonstrated for conducting fieldmeasurements to quantify the ratio of in-vehicle to outside vehicle concentration (I/O) for a widerange of conditions that affect intra-vehicle variability in exposure concentration. A field datacollection study design is developed based on sources of intra-vehicle variability in I/O,including ventilation air source, window status, fan setting, AC utilization, vehicle speed, roadtype, travel direction, and time of day. Three replicates of measurements were made for 16combinations of these factors on 110 miles of roads comprised of eight one-way routes betweentypical commuter origin/destination pairs. Two portable particle monitors recorded in-vehicleand near-vehicle ambient concentrations on one minute averages for four particle size ranges.The comparability of the monitors was quantified. Near-vehicle concentrations varied with roadtype, time of day, and traffic conditions. The I/O ratio was approximately independent of near16vehicle concentration, and varied with window status, source of ventilation air (fresh orrecirculation), and, for cases with recirculation and closed windows, fan setting and airconditioning use. The study design can be extended to additional vehicles to account forpotential sources of inter-vehicle variability. Data such as collected here can be used to improveexposure simulation models.