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Principal Investigator: Charles Rodes, Ph.D.
Research Triangle Institute
December 1998
ARB Contract No. 95-339 (Full Report)
ABSTRACT
Researchers measured pollutant concentrations inside vehicles on California roadways during 32 driving trips
in the cities of Los Angeles and Sacramento. For most of the pollutants, two-hour integrated samples were collected
concurrently inside the vehicle, just outside the vehicle, along the roadway where the vehicle traveled, and at
ambient monitoring sites. Pollutants measured included PM10 and PM2.5 metals, and 13 organic chemicals including
benzene, MTBE, and formaldehyde. In addition, the researchers obtained continuous measurements of fine particle
counts, carbon monoxide (CO), and black carbon. The driving scenarios were designed to evaluate the association
between in-vehicle pollutant levels and factors such as the carpool lane, traffic congestion, vehicle type, road
way type, time of day, and ventilation setting.
In-vehicle pollutant levels were generally higher in Los Angeles than Sacramento. In Los Angeles, the average in-vehicle
concentrations of benzene, MTBE, and formaldehyde ranged from 10-22 µg/m3, 20-90 µg/m3, and 0-22 µg/m3,
respectively. In Sacramento, the average in- vehicle concentrations for benzene, MTBE, and formaldehyde ranged
from 3-15µg/m3, 3-36 µg/m3, and 5-14 µg/m3, respectively. The ranges of mean PM10 and PM2.5 in-vehicle
levels in Los Angeles were 35-105 µg/m3 and 29-107 µg/m3, respectively. The ranges of mean PM10 and
PM2.5 in-vehicle levels in Sacramento were 20-40 µg/m3 and 6-22 µg/m3, respectively.
In general, VOC and CO levels inside or just outside the vehicles were higher than those measured at the roadside
stations or the ambient air stations. However, in-vehicle levels of PM2.5 were consistently lower than PM2.5 levels
just outside the vehicles and, in many cases, also lower than roadside levels. Nonetheless, PM2.5 levels inside
or just outside the vehicles were usually higher than levels measured at the nearest ambient site. Except for sulfur,
metal concentrations were generally low or below detection limits. Pollutant levels measured inside vehicles traveling
in a carpool lane were significantly lower than those in the right-hand, slower lanes. Under the study conditions,
factors such as vehicle type and ventilation settings were shown to have little effect on the in-vehicle pollutant
levels. Other factors, such as roadway type, freeway congestion level, and time-of-day were shown to have some
influence on the in-vehicle pollutant levels. Elevated levels of both fine particles and black carbon were measured
inside the test vehicle when it followed diesel-powered vehicles.
This study provided the data needed to characterize in-transit exposures to air pollutants for California drivers.
It also demonstrated a number of in-situ monitoring techniques in moving vehicles and provided findings that shed
new light on particle exposure assessments and research needs.
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