# Assessment of Daily Personal PM2.5 Exposure Level According to Four Major Activities among Children
## 5 Conclusions and Limitation  
This study demonstrated that our methodology of incorporation of PM2.5 data obtained at 10 s intervals and a database of personal daily activity pattern diaries is a useful and feasible method for improving our understanding on the daily variation of exposure levels per person or activity. Our approach introduced in this paper could improve the characterization of exposure patterns and provide a potential person-specific management strategy to reduce a person's exposure level. In general, a sensor-based study should be interpreted with care. A real-time inexpensive sensor-based approach is convenient to obtain various exposure levels with improved spatial and temporal resolution but it does not guarantee accuracy or precision of the outcome unless a no data quality control procedure is applied. It has been well established that the response of monitoring devices based on light scattering varies with aerosol size distribution, composition, and optical properties need a proper calibration process [27; 28; 29]. No single calibration can enable an accurate performance for all particle sources related to diverse activities in microenvironments. Due to our previous comparison test between MicroPEM and Sidepak or PDR-1500 measuring PM2.5 indoors with panfrying and secondhand smoke exposure, we had the experience that MicroPEM was a little noisy but gave comparable results after applying a correction factor. Even though RTI MicroPEM can provide gravimetric measurements but with the daily short sampling duration being limited, applying the gravimetric method for every single site is not practical for routine personal monitoring. Although we compared self-reported activity patterns with GPS records of longitude and latitude, future advanced tracking technologies with GPS may be helpful and convenient to estimate a person's activity pattern. The three weeks were not mutual for every subject; however, as data collection was conducted from October 2018 to March 2019, those who provided activity data for at least three weekdays were included in the analysis of this study. We originally planned to conduct personal monitoring mutually but owing to the lack of the same monitoring devices, we could not do so. We conducted this study with 15 study participants. Future studies with better sample size need to focus on integration of PM2.5 data with health (respiratory or cardiovascular diseases) databases to provide insights for the reduction of the burden of diseases related to exposure to PM2.5. As technology continues to improve the capability of inexpensive sensor based personal monitoring, more opportunities will be presented to mine raw data and integrate data into personal health outcomes and current government policies. Personal particulate monitors will become more popular among the susceptible population with underlying susceptible respiratory and cardiovascular conditions who want to monitor particulate levels in order to protect their own health. Integrated personal exposure profiles or combining such profiles, the so called community exposure profile would certainly be valuable to policy makers, as having more detailed data on the polluted microenvironment can motivate policy changes toward PM2.5 reduction. Our study demonstrated that personal-level monitoring with advanced technologies, combined with data analysis skills is very useful to explore and identify local pollution sources. **Author Contributions:** Conceptualization, S.K. ; methodology, S.K. and J.W. ; data analysis, J.W. ; resources, S.K. ; data curation, S.K. ; writing--review and editing, S.K., J.W., and G.R. ; visualization, J.W. and G.R. ; project administration, S.K. ; funding acquisition, S.K. All authors have read and agreed to the published version of the manuscript. **Funding:** This study was funded by the Environmental Health Research Center Project (2016001360003) by the Korea Environmental Industry and Technology Institute, Ministry of Environment, South Korea.