Association between respiratory tract deposited dose of size-segregated PM and FeNO based on individual exposure assessment for Korean children.

FeNO (fractional exhaled nitric oxide) is a crucial marker to understand children's respiratory diseases such as asthma, and severity may vary depending on PM diameter and respiratory tract region. This study investigates the relationship between size-segregated respiratory deposited PM dose and FeNO for children. Size-segregated PM (PM1.0, PM1.0-2.5, and PM2.5-10.0) and FeNO were measured for eighty children based on individual exposure assessment in five consecutive days. Individual physical activity was measured by an accelerometer device. Accordingly, a dosimetry model estimated the respiratory deposited dose by PM diameter in the extrathoracic (ET), tracheobronchial (TB), and pulmonary (PUL) regions. A linear mixed model (LMM) with distributed lag non-linear model (DLNM) was used for analysis. The effects of home environment and traffic-related factors were also examined for sensitivity analysis. We found that IQR increases of PM2.5-10.0 and PM1.0 were associated with 15.1 % (95 % CI: 3.5, 28.1) and 15.9 % (95 % CI: 2.7, 30.9) FeNO increase in respiratory Total region in 0-12 h lag. In cumulative lag 0-24 h, PM1.0 was only associated with FeNO increase: 16.6 % (95 % CI: 1.5, 34.1) in total region. No association was observed in lag 12-24 h. PM2.5-10.0 was related to short-term airway inflammation in the upper respiratory tract whereas PM1.0 has a cumulative effect on both the upper and lower respiratory tract. In sensitivity analysis, PM2.5-10.0 was associated with a 0-12 h lag, whereas both PM2.5-10.0 and PM1.0 were associated with a cumulative lag of 0-24 h. Both home environment and traffic-related factors showed a synergetic effect with PM1.0 in short-term exposure and an antagonistic effect with PM2.5-10.0 in long-term exposure. This study highlights that airway inflammation depends on PM sizes, exposure durations, and respiratory tract regions.