Research Projects

Project at a Glance

Title: Measuring concentrations of selected air pollutants inside California vehicles

Principal Investigator / Author(s): Rodes, Charles

Contractor: Research Triangle Institute

Contract Number: 95-339

Research Program Area: Health & Exposure, Emissions Monitoring & Control

Topic Areas: Indoor Air Quality, Mobile Sources & Fuels


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 g/m3, 20-90 g/m3, and 0-22 g/m3, respectively. In Sacramento, the average in- vehicle concentrations for benzene, MTBE, and formaldehyde ranged from 3-15g/m3, 3-36 g/m3, and 5-14 g/m3, respectively. The ranges of mean PM10 and PM2.5 in-vehicle levels in Los Angeles were 35-105 g/m3 and 29-107 g/m3, respectively. The ranges of mean PM10 and PM2.5 in-vehicle levels in Sacramento were 20-40 g/m3 and 6-22 g/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.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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