2019 Yes https://www.sciencedirect.com/science/article/pii/S0160412019312231 Mazaheri, Mandana Asia Observational Modeling Students Elementary (K-5) Ultrafine particles Personal exposure School children Indoor air quality Indoor exposure Second-hand smoking Hourly average UFP concentrations exhibited three peaks in the morning, midday and evening. Time spent indoors at home was found to have the highest average exposure (1.26 × 104 cm−3 during sleeping) and exposure intensity (2.41). While there is always infiltration of outdoor particles indoors (from nearby traffic and general urban background sources), indoor exposure at home was significantly higher than outdoor exposure. Based on the collected questionnaire data, this was considered to be driven predominantly by adults smoking and the use of mosquito repellent incense during the night. Outdoor activities at school were associated with the lowest average exposure (6.87 × 102 cm−3) and exposure intensity (0.52).