LAUSR

This study provides an investigation of atmospheric PM2.5, PM10, SO2, NO2, CO, and O3 in the period from 2015–2017 in the southwestern and central part of Taiwan. In addition, the seasonal distribution of six AQI classes and corresponding primary pollutants were further analyzed. The daily AQIs were 15–194 in 2015, 17–213 in 2016, and 16–184 in 2017, respectively. During the three year period, in the studied area, the mean proportions of levels with Grade I, II, III, IV, V, and VI were 3%–31%, 30%–57%, 17%–46%, 0%–12%, 0%–1% and 0% in spring; were 38%–76%, 21%–57%, 0%–10%, 0%–2%, 0% and 0% in summer; were 2%–45%, 34%–77%, 13%–36%, 0%–18%, 0% and 0% in fall, and were 0%–12%, 38%–67%, 24%–41%, 1%–22%, 0% and 0% in winter. Generally, it was found that summer has the best air quality and that winter has the worst, where spring and fall are similar in terms of air quality. PM2.5 was the typical primary air pollutant when the AQI classes were 51–200, followed by O3 in summer, spring and fall, and PM10 in winter. As for class 201–300, the primary air pollutant was O3 and the 300–500 class did not occur.