Time Series Assessment of PM2.5 Source Contributions and Classification of Haze Patterns in Seoul

Huge hourly PM2.5 datasets monitored at the Seoul Intensive Monitoring Station (SIMS) during Jan. 1, 2013 to Dec. 31, 2014 were obtained from the National Institute of Environmental Research (NIER). A total of 12,376 samples consisting of 24 chemical variables and 3 meteorological variables had been applied for the positive matrix factorization (PMF) modeling based on a dataset segmentation scheme in the previous study (Park et al., 2019). After performing the receptor model, 14 independent PM2.5 sources were successfully identified and quantified at the SIMS. In this study, based on the meteorological variables and the previous PMF results, we assessed intensively the PM2.5 source contributions by time sequential analyses such as hourly, daily, weekly, monthly, and seasonal analyses and further we classified haze patterns into 3 types such as foreign-oriented type, domestic-oriented type, and mixed type, judging from PM2.5 source contribution. According to our intensive study on wintertime haze cases, all the episode events in Seoul area initially began with rapid and big air temperature drop for several days and then high PM2.5 concentration appeared right after rapid and big air temperature rise until air temperature rose again, which forming frontal inversion with slower wind speed and then lowering a mixing height causing concentration buildup. The most dominant PM2.5 source among 14 identified sources in Seoul area was secondary aerosol source, which was considered to be transported distantly from overseas. The seasonal source contribution was summer 15.8 μg/m³, spring 14.4 μg/m³, winter 10.4 μg/m³, and fall 5.4 μg/m³ in mass order. On the other hand, secondary nitrate source as another secondary aerosol was identified as one of domestic sources. The range of seasonal source contribution was in the range of 1.0∼2.4 μg/m³ and further weekly and monthly variations were relatively small. However, its hour variation was greatly changed, up to 4.5 μg/m³ during nighttime. We hope that the results of the study can be used as basic information whenever establishing reasonable air quality management and policy in Korea.