Indoor and outdoor PM_2.5 exposure, and anxiety among schoolchildren in Korea: a panel study

This panel study aimed to evaluate the associations between short-term exposure to indoor and outdoor PM_2.5 and anxiety in schoolchildren. During 3 waves in March, July, and November 2018 with 7 days per wave, 52 children aged 10 years were recruited from two schools in a city in Korea. To assess outdoor exposure, we used PM_2.5 concentration measures for every hour at the national measurement station (NMS) closest to the two participating schools. To assess indoor exposure, we measured PM_2.5 concentration at the children's homes and in classrooms, based on 30-min average. Based on time-activity logs, personal average daily exposure values were calculated for each participant, according to exposure values assessed at 30-min intervals by location. Children's anxiety was assessed via the Korean version of the State Anxiety Inventory for children every day during each wave. Linear mixed effects model was conducted to analyze the association between PM_2.5 exposure and anxiety using repeated measurements. Personal exposure to PM_2.5 by time-activity log was the highest in March and at home. A low correlation coefficient was observed between PM_2.5 concentrations at home and at the NMS (ρ = 0.36, p < 0.0001) whereas a high correlation coefficient was observed between PM_2.5 concentrations in classrooms and at the NMS (ρ = 0.64, p < 0.0001). There was no association between PM_2.5 exposure and anxiety in children based on the analysis of repeated measurements during the study period. Since previous studies reported controversial results, long-term follow-up studies are needed in various regions to further investigate the associations between PM_2.5 exposure and children's mental health.