# Assessment of Daily Personal PM2.5 Exposure Level According to Four Major Activities among Children
## 1 Introduction  
For decades, particulate matters with aerodynamic diameters less than 2.5 micrometers (PM2.5) have attracted significant attention in the Republic of Korea. According to the Ministry of Environment, the national average concentration of PM2.5 increased from 28 \(\upmu\)g/m\({}^{3}\) in 2015 to 30 \(\upmu\)g/m\({}^{3}\) in 2016, and reached 31 \(\upmu\)g/m\({}^{3}\) in 2017 [1] which is three times higher than the World Health Organization (WHO) annual guideline(10 \(\upmu\)g/m\({}^{3}\)) [2]. Various environmental epidemiology studies have identified significant positive associations between exposure to airborne PM2.5 and the exacerbation of chronic or acute disease symptoms [3; 4], increased mortality risk [5], decreased life expectancy [6], and low birth weight [7]. According to the report on the global burden of disease by the WHO, PM2.5 was the ninth major risk factor of disease burden in the Republic of Korea [8] and has been shown to increase the risk of cardiovascular and respiratory diseases, and even premature deaths among Koreans [9]. In general, variation of ambient PM2.5 level is associated with the degree of urbanization, industrialization, and transport as well as ambient chemical reactions under certain meteorological conditions. This implies that a high percentage of people living in Korea are at increased risk of exposure to high levels of PM2.5 as well as adverse health risks as the majority of the population live in urban or industrial areas. Therefore, these days, according to Korean policy makers or other stakeholders, the primary goal of air pollution control policy is to reduce, or ideally eliminate adverse health effects resulting from air pollutants.  
The development of an air pollution control policy requires accurate assessment of potential exposure levels according to time and place. The evaluation of the exposure level to PM2.5 within a susceptible population depends critically on how people spend their time at specific sites relating to their activity pattern. Errors in exposure estimation, caused by relying on proxies of approximate exposure duration or level for specific microenvironment, may lead to significant bias in the estimation of related health burdens and developing control policies.  
Traditional methods for measuring exposure have sometimes required bulky, heavy, and noisy monitors as well as sophisticated laboratory setups. Alternative approaches relying on sensor-based small portable real-time samplers with activity tracking information can provide a substantial improvement [10] compared with traditional approaches in determining the level of PM2.5 exposure depending on the activities conducted in the specific microenvironments. With recent technology development, a few studies have reported the association of PM2.5 exposure level with time activity patterns in Scotland [11], Portugal [12], India [13], and the United States [14]. Such previous study results indicated that PM2.5 exposure levels were different due to substantial variability of time spent in microenvironments and emphasized personal measurement of near exposure pathways to allow a comprehensive evaluation of the exposure risk which a person might encounter on a daily basis.  
In Korea there are still very limited studies that have assessed PM2.5 exposure according to children's activity. Although their daily activity patterns may be different to other countries due to different social conditions or norms i.e., high interest in early education and development resulting in young children attending several types of private education institutes or pre-schools. In this study, we evaluated children's exposure level to PM2.5 by incorporation of PM2.5 data obtained at 10 s intervals and a database of the personal daily activity patterns.