# Assessment of Daily Personal PM2.5 Exposure Level According to Four Major Activities among Children
## 4 Discussion
This study found that children's daily PM2.5 dose at educational institutes (43.3 \(\upmu\)g) was approximately half of the amount received at home (88.9 \(\upmu\)g) while the ratio of exposure duration at the education institute to that at home was 0.37 (27.2 \(\pm\) 14.4% vs. 72.7 \(\pm\) 18.7%) indicating that indoor air quality at the education institute or home could determine children's highest exposure level. Thus, application of a management action, i.e., the indoor PM2.5 control strategies for various microenvironments including education institutes as well as homes is immediately necessary to reduce children's exposure to PM2.5 and minimize the risks of potential health effects arising from exposure to PM2.5. On March 2019, the South Korean government passed a revised school health act to improve indoor air quality at pre-schools and primary and secondary schools. By law, the installation of air-cleaning systems and air quality monitoring sensors in classrooms with state government funds is required. A future study on a policy impact assessment is expected. [PERSON] et al. (2017) have reported the median (interquartile range) of the ratio of PM\({}_{2.5}\) concentrations with one or two windows open, or with a cooker stove hood operating at concentrations without ventilation: 0.63 (0.40-0.69), 0.41 (0.23-0.56), or 0.17 (0.08-0.25), with dissipation kinetics ((\(\upmu\)g/m\({}^{3}\))/min) of 6.5, 20.1, 17.0 or 26.6 respectively, after completion of cooking at an inside Korean apartment [21]. Related to our study results, further studies are recommended to figure out the determinants of indoor air quality at home. Especially, it is highly suggested to conduct a future study to determine the existence of an interactive effect between operating an air purifier and conducting ventilation in a typical classroom and a house in Korea. Also, indoor variation of PM2.5 by children's indoor action (walking or running) at education institutes, and that by infiltration of PM2.5 from outside to inside should be further investigated [22]. A similar outcome has been obtained from personal monitoring with adult study populations. (India [13], Scotland [11] and US [14]) implying that like children, among adults also, as measurements were taken across the heterogeneity of indoor microenvironments, tracking activities influencing personal exposure level to PM2.5 is considered more accurate for exposure data [11]. In this study, we used inexpensive personal monitors i.e., MicroPEM. This monitor was previously evaluated by [PERSON] et al. (2017) [11]. They reported that performance of MicroPEM was comparable to that of a research-grade expensive portable monitor i.e., SIDEPAK; According to [PERSON] et al., for  
Figure 3: Daily accumulated PM2.5 exposure amount per activity and per person. personal samples, 24-h mean PM2.5 concentrations with the MicroPEM were 6.93 ug/m\({}^{3}\) (standard error = 0.15) and that for SidePak was 8.47 ug/m\({}^{3}\) (standard error = 0.10). In this study, as we mentioned in the method section, we calibrated the MicroPEM before use in the field. The final concentration was provided after adjusting for values of temperature and relative humidity as we did for other inexpensive portable sensor based monitors [23]. In this study, we adopted the continuous monitoring outcomes with a 10 s interval. From the outcomes, we found that data pre-processing was an essential step for maintaining the accuracy of data. Stationary or mobile monitoring data have been often used for estimating exposure level to PM2.5. However, there is a certain limitation of coverage with those stationary monitoring sites. Using a simple but standardized protocol of devices and data mining technologies, more precise and accurate exposure assessment results can be provided to policy makers and the susceptible population [24; 25; 26].