Identification of nitrogen dioxide and ozone source regions for an urban area in Korea using back trajectory analysis

The NO₂ and O₃ in an urban background site of Seoul, Korea (Yongsan), were analyzed using hourly data collected from 2005 to 2013. The potential role of meteorological parameters in controlling air quality at the receptor site was analyzed using a conditional probability function. In addition, the relative contributions of such variables were examined for special cases (i.e., more than 60 ppb of NO₂ and O₃) with the help of trajectory. A potential source contribution function with a grid size resolution of 0.25° × 0.25° was used to determine the potential exogenous sources of NO₂ and O₃ for the study area. The results of both the trajectory and potential source contribution function analyses suggest that both the northern China region and local emission sources are the most influential source pathways contributing to the recent increase in NO₂ concentration at the study site. In the case of O₃, this role was shared by both oceanic and mountainous regions of China and Japan.