Characteristics of PM2.5 Chemical Composition and High-concentration Episodes Observed in Jeju from 2013 to 2016

From 2013 to 2016, the characteristic variations of PM2.5 chemical composition and high concentration episodes were investigated at the Jeju Air Quality Research Center. The average concentration of PM2.5 was 18.6 +/- 16.1 mu gm(-3) for the entire period and the annual average concentration showed about 30% decrease from 2013 to 2016. Accordingly, the concentrations of secondary inorganic ions including NH4+, SO42-, and NO3- decreased as well, whereas OC concentrations did not show significant annual changes. The high PM2.5 event, which exceeded 24-hr Korean PM2.5 standard of 35 mu gm(-3) ("bad"), was frequently observed in cold months between December and March and also in May. In particular, the NO3- concentration was noticeably elevated when 24-hr average PM2.5 concentration was observed to be higher than 75 mu gm(-3) ("very bad"), and the air masses during the very bad condition originated mostly originated in the eastern regions of China such as Shandong and Shanghai, which was confirmed by concentration weighted trajectory (CWT) analysis. For the PM2.5 bad case (36 similar to 75 mu gm(-3)), the concentrations of SO42-, NO3-, and OC were enhanced in association with air masses transported from the Korea peninsula and Shanghai region, Shandong and Bohai Bay areas, and Liaoning regions, respectively. NH4+ had the best correlation with PM2.5, and showd that it is well neutralized with SO42- and NO3-.