Predictive Meteorological Factors for Elevated PM2.5 Levels at an Air Monitoring Station Near a Petrochemical Complex in Yunlin County, Taiwan

Since 1991, air pollution has gained special attention in Taiwan after a petrochemical complex was constructed in Mailiao Township, Yunlin County. We explored the association between the magnitude of PM2.5 and meteorological factors during 2012-2016. Our findings revealed that 1) mean PM2.5 levels gradually decreased from 30.70 μg/m3 in 2013 to 25.36 μg/m3 in 2016; 2) wind speed is the main determinant of air quality—air quality significantly improved when it was faster than 4 m/sec; and 3) wind direction is another determinant of air quality—when the wind direction was southerly, air quality improved. Elevated PM2.5 levels were defined as those hourly levels higher than the third quartile (36 μg/m3). The significantly negative predictive factors for elevated PM2.5 levels were the summer or autumn seasons, rainfall, increased wind speed, and wind direction from 150° to 230° from the north. The significantly positive predictive factors for elevated PM2.5 levels were working hours from 6 a.m. to 2 p.m., a temperature between 11°C and 25°C, relative humidity between 40% and 68%, and wind direction (e.g., northerly wind, northeasterly wind, and easterly wind). The predictive formula is attached in the Appendix. Therefore, people should protect themselves on these high-risk days.