Historically, the difficulty in epidemiologic studies has been that the only available air pollution data originated from central regional ambient sites, which may not be representative of personal exposures, resulting in imprecise associations.
Data include 376 person-days of daily endotoxin data collected from PM2.5 quartz filters using personal exposure monitors operated at 4 L/min, daily ambient endotoxin measurements collected from central ambient sites, and daily indoor and outdoor home endotoxin measurements in a subset of 14 children at 12 residential sites in Riverside and Whittier, California.
Epidemiological studies relating air pollution to health effects often estimate personal exposure to particulate matter using values from a central ambient monitoring site as a proxy.
Outdoor concentrations were also measured at a stationary ambient monitoring site.
The correlation between residential outdoor coarse PM mass concentrations and those obtained from the central ambient monitoring site were typically greater than r = 0.75.
This spatial variation may result in exposure misclassification because participants lived 22 km on a median straight line distance from our ambient monitoring site.
This finding suggests that in epidemiological time-series studies, the use of one single ambient monitoring site is an adequate approach for characterizing exposure to ultrafine particles.
Our study is limited by our use of air pollution measurements from a single stationary ambient monitoring site as our exposure measure, which may cause exposure misclassification.
Hazard ratios (HRs) for new-onset asthma were scaled to the range of ambient central site pollutants and to the residential interquartile range for each traffic exposure metric.
One limitation of our study is the use of a single ambient monitoring site as a surrogate for recent ambient pollution exposure, which will not capture spatial variation in air pollutant concentrations.
