Personal Exposure to Ultrafine Particles According to Different Environments and Modes of Transport in Schoolchildren: Results from a Spanish Cohort in Valencia

Background Combustion, especially in diesel engines, emits a complex mixture of gases and particles that could be harmful for the respiratory and cardiovascular systems. Daily personal exposure to the smallest particulate matter (less than 0.1 µm and usually called nanoparticles or ultrafine particles – UFP) has been studied to a lesser extent compared to coarser particles. In this study we aim to assess personal exposure to UFP in different environments and transport modes among schoolchildren from a Spanish birth-cohort in the province of Valencia. Methods The study population consisted of 114 children aged 10-11 years. For each of them, personal exposure to UFP was measured continuously during two successive school days (24 hours) by means of a small backpack equipped with a UFP active sampler (DISCmini). The first day, a technician delivered the required material to the child’s home and instructed them on the monitoring period. The second day, families came to the health center where children underwent health examinations and parents answered questionnaires about time-activity patterns, sociodemographic factors, and other exposures. Median UFP exposure levels (numbers of particles per cm 3 – N/cm 3 – were obtained for the overall period, for different environments (at home and school) and during journeys by different modes of transport (active transport – walking or cycling – or passive transport – car, bus, metro or tram). Results Around 90% (N=101) of the schoolchildren had valid exposure data (at least at home and school). Mean monitoring time was 24 hours [range: 22-27 hours]. Participants spent 15 hours at home, 6 hours at school, 28 minutes in active transport, and 60 minutes in passive transport on average during the monitoring period. Passive transport in our study was over-represented since on the second day of the visit most families drove to the health center. Over this period, DISCmini obtained valid data for 98.5% of the time [interquartile range: 80.1%-100.0%]. Global personal exposure level was 9368 N/cm 3 [interquartile range: 5514-17607 N/cm 3 ], being higher during the cold season. Personal exposure levels were higher during journeys (especially in passive transport) than in other environments. Comparing exposure levels at home and school, UFP levels were higher at home, probably due to burning appliances (e.g., gas cooker). Conclusions Schoolchildren were exposed to a wide range of UFP levels. Personal exposure levels varied across the studied environments, being higher during journeys and especially in passive modes of transport.