According to recent studies, the health effects (relative risk) of PM can vary over time, and recent health effects showed a decreased temporal trend. However, the causes of the temporal heterogeneity in PM10 effects have not been studied yet. In this thesis, the author aimed to estimate possible causes of the recent decrease in PM10 relative risk for respiratory mortality and morbidity in Korea. The first study estimated the effects of the PM10 alert system on people's outdoor activity patterns in Seoul, Korea. The system aims to reduce personal PM exposure by predicting the ambient PM concentration in advance and warning people to take avoidance behaviours when episodic spikes in PM concentration are expected. But as most epidemiologic studies use ambient PM concentration as a surrogate of personal exposure, introducing a PM alert system can increase the measurement error in exposure assessment. The effects of policy on the number of urban park visits were evaluated using segmented regression, and the result showed an 11% decrease in park visitors when the "Bad" alert was issued. The result may indicate a possibility that the recent decrease in PM10 relative risk might partly be attributable to increased measurement error between the ambient PM concentration and personal exposure. In the second analysis, the effects of temporal change in socioeconomic variables and PM2.5 compositions on temporal heterogeneity were investigated using a two-level random intercept model. The result indicated that change in medical infrastructure was significantly associated with the temporal change in PM10 mortality risk for respiratory disease, and the change in economic status was associated with a change in PM10 effects for respiratory outpatients. The reduction in PM10 relative risk might be a remarkable achievement from the public health perspective. Although the early response of the Korean government to PM was focused on regulating ambient concentration, the future strategy would be targeted to manage the PM risk. In this process, the author wishes that the result of the thesis might provide a scientific basis to help establish a more proper and reasonable strategy for managing the risk of PM.