Indoor-outdoor behavior and sources of size-resolved airborne particles in French classrooms

Indoor and outdoor airborne particles were monitored with a 5-s time resolution in three elementary schools presenting different site typologies (rural, urban, and industrial) in the North of France. We studied the influence of the children's activities, outdoor sources, temperature and relative humidity on particle mass concentrations and particle mass size distribution, and estimated cancer risk regarding particle composition. The indoor weekly mean PM10 mass concentrations during teaching hours varied from 70 to 99 mu g m(-3), exceeding the French daily recommended value of 50 mu g m(-3), implying a potential impact on the respiratory system. However, fine particles (<2 mu m) were always below French daily recommended value of 25 mu g m(-3) applied to PM2.5. The results showed that children's activities impacted the suspended coarse fraction (2-10 mu m) more strongly than the fine one (<2 mu m). The mass distribution of indoor PM10 was extremely variable in association with occupant's activities in classrooms whereas the outdoor one seemed to be only lightly variable. During lessons, average concentrations of indoor PM1, PM1-2, PM2-5, and PM5-10 increased respectively by factors of 2.9, 3.1, 8.7 and 33.8 compared to unoccupied periods. Indoor sources from continuous emission and occupant's activities may lead to lower density of indoor PM10 compared to outdoor ones. The estimation of some potential carcinogen elements such as As, Cd, Cr, and Ni in indoor PM2 showed low concentrations in the range of 0.11-1.71 ng m(-3). Consequently, the cancer risk of these elements was estimated to be not significant for long-term exposure to both children and teachers. (C) 2014 Elsevier Ltd. All rights reserved.