In-vehicle exposures to particulate matter (PM) and blackcarbon (BC) can be a significant part of personal totalexposure. The purpose of this study was to identify deter-minants of the in-vehicle pollutant level. This study mea-sured in-vehicle exposure to PM number concentrationsusing an aerosol spectrometer and BC concentration byan aethalometer. The measurement was repeated 3 timesa day for 13 consecutive days in May 2007 while a vehiclewas driven on a 1-hr predetermined route in Lexington,KY. The vehicle's windows were closed, its fan was oper-ated at the lowest setting, and air conditioning and heat-ing were off. The average speed of all runs was 37 ± 5.8km/hr. Arithmetic mean PM_1(particle sizes ≤1 μminaerodynamic diameter) number and BC concentrationswere 286 #/cm~3(morning, 302 #/cm~3; afternoon, 270#/cm~3; evening, 287 #/cm~3) and 1.9 μg/m~3(morning, 2.5μg/m~3; afternoon, 1.6 μg/m~evening, 1.5 3), re-spectively. Average PM and BC concentrations increasedduring weekdays and decreased during weekends, andPM, number and BC concentrations were highest in themorning. Particle size distribution for PM_1did not differwith time of day, but the concentration of PM_(1-10)(parti-cle sizes between 1 and 10 μ m in aerodynamic diameter)was higher in the evening and lower in the morning. PeakPM_1number concentrations were observed when the testvehicle approached busy crossroads. In-vehicle PM andBC concentrations were associated with time of the dayand location, whereas the in-vehicle 1-hr PM numberconcentrations were closely associated with distant ambi-ent PM_(2.5)(particle sizes ≤2.5 μm in aerodynamic diame-ter) concentrations measured at a stationary monitoring site. The findings suggested that in-vehicle exposure isassociated with surrounding traffic.
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