Sources of Variability in Real-Time Monitoring Data for Fine Particulate Matter: Comparability of Three Wearable Monitors in an Urban Setting

The increasing availability of portable air pollution monitoring devices has greatly enhanced the ability to measure personal exposure in real time. However, the cost and specifications of these devices vary considerably, and questions about their reliability and practicality for use in epidemiological investigations remain. In this field study, three personal PM2.5 exposure monitors (two nephelometers and one optical particle counter) were compared in an urban setting to assess their feasibility for use in future studies. In total, 3963 1-min measurements were collected over 12 days from locations of several types (e.g., above- and below-ground subway stations, sidewalks next to urban traffic, outdoor construction sites, etc.) in the Washington, DC, metropolitan area. Overall, we observed moderate to high levels of agreement in pairwise comparisons of PM2.5 concentrations between devices (R 2 range of 0.37–0.75). Bland–Altman plots showed that differences in device agreement varied over the range of mean concentrations. In linear mixed models adjusting for temperature and relative humidity, we saw significant interaction between the device and location (p < 0.05), suggesting that the relationship between devices was not constant in all locations. Our finding of heterogeneity in instrument comparability by location may have important implications for epidemiologic studies incorporating personal PM2.5 measurements.