Centralized outdoor measurements of fine particulate matter as a surrogate of personal exposure for homogeneous populations

Fixed-site monitoring of particulate matter is often used as a surrogate of individual-level exposure, due to the high cost and logistic inconvenience of personal monitoring. However, studies have been limited to validate this approach in specific populations. This study aims to corroborate that centralized outdoor measurements of fine particulate matter (PM2.5) can be a surrogate of personal exposures in individuals living in a non-industrial area with high outdoor PM2.5 concentrations. The personal exposure monitors (PEMs) were first validated with a reference high-volume Andersen sampler for PM2.5 sampling. Then personal samples were collected on 113 nonsmoking participants in Beijing, China, over a period of 3.5 years. Simultaneously, outdoor PM2.5 samples were collected at a central urban location. Indoor PM2.5 samples were also collected in select microenvironments where study participants frequently stayed. PM2.5 was collected onto a 37 mm quartz fiber filter in the PEM, and the mass was determined gravimetrically. Participants recorded their time-activity patterns. PEM measurements showed a high correlation with measurements from the regulatory reference method (R-2 = 0.98, slope = 1.21, and a non-significant intercept). PM2.5 had mean concentrations of 196, 139, and 156 mu g/m(3) in outdoor, indoor and personal air, respectively. Personal exposures displayed large within-person variability (97.5% of the total variance) and negligible between-person variability (2.5%). Personal exposures were determined by outdoor concentrations (p < 0.0001), but not by indoor concentrations or the time activity pattern (p > 0.05). Linear regressions show that outdoor concentration contributed 72% of personal exposure and explained 84% of variability of personal exposure. We conclude that centralized outdoor measurement of PM2.5 is a good surrogate of personal exposure; however, the overestimation of personal exposure using outdoor concentration warrants the need for personal monitoring if the actual exposure (amount) is needed. In populations of similar lifestyle, focusing on longitudinal measurements, rather than measurements in a large number of individuals, would be a more effective exposure assessment approach, given that personal exposure variability was largely driven by temporal variability.