Assessment of Microenvironmental Exposures to Ultrafine Particles among Adolescent Schoolchildren

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Background: Assessing personal exposure to ultrafine particles (UFPs) is challenging due to multiple indoor and outdoor sources and high spatiotemporal variation. Our objective is to characterize personal UFP exposures experienced by adolescents enrolled in the Ecological Momentary Assessment and Personal Particle Exposure Study (EcoMAPPE). Methods: Participants (ages 13-17) complete a seven-day sampling period using a personal UFP monitor for 3 hours each day that simultaneously records GPS-based location at 1-second resolution. Measured UFP concentrations are assigned to microenvironments based on speed and distance from participant specified locations: schools (400m), homes (100m), and other (100m) locations. UFP concentrations measured outside these areas exhibiting speeds greater than 2 m/s are categorized as occurring while in transit. We define the percent contribution of each microenvironment to a participant’s overall exposure as the summation of UFP concentration in a specific microenvironment divided by the summation of all recorded UFP concentrations. Lastly, we derive exposure-time ratios by dividing the percent contribution of each microenvironment by the percentage of time spent within each microenvironment. Results: Complete sampling and location data is available for 21 participants, representing 378.5 hours of UFP data. The overall median UFP concentration is lowest at home (4,500 particles/cm3), while school/other (5,990), and transit concentrations (7,960) are higher. Most UFP measurements are recorded at home (70%), followed by school/other locations (23%), and transit (7%). Participants experience median exposure-time ratios of 0.99 (Q1: 0.90; Q3: 1.04) at home, 0.82 (0.45; 1.21) at other locations, and 1.10 (0.62; 1.73) in transit.Conclusion: Despite the low percentage of time spent in transit, most participants experience UFP concentrations during transit that contribute more to their overall exposure in comparison to other microenvironments.